Sickle cell disease (SCD) is characterized by intermittent vaso-occlusive events and chronic hemolytic anemia. Vaso-occlusive events result in tissue ischemia leading to acute and chronic pain as well as organ damage that can affect any organ system, including the bones, spleen, liver, brain, lungs, kidneys, and joints. Dactylitis (pain and/or swelling of the hands or feet) is often the earliest manifestation of SCD. In children, the spleen can become engorged with blood cells in a "splenic sequestration." The spleen is particularly vulnerable to infarction and the majority of individuals with SCD who are not on hydroxyurea or transfusion therapy become functionally asplenic in early childhood, increasing their risk for certain types of bacterial infections, primarily encapsulated organisms. Acute chest syndrome (ACS) is a major cause of mortality in SCD. Chronic hemolysis can result in varying degrees of anemia, jaundice, cholelithiasis, and delayed growth and sexual maturation as well as activating pathways that contribute to the pathophysiology directly. Individuals with the highest rates of hemolysis are at higher risk for pulmonary artery hypertension, priapism, and leg ulcers and may be relatively protected from vaso-occlusive pain.

Chediak-Higashi syndrome (CHS) is characterized by partial oculocutaneous albinism, immunodeficiency, and a mild bleeding tendency. Approximately 85% of affected individuals develop the accelerated phase, or hemophagocytic lymphohistiocytosis, a life-threatening, hyperinflammatory condition. All affected individuals including adolescents and adults with atypical CHS and children with classic CHS who have successfully undergone allogenic hematopoietic stem cell transplantation (HSCT) develop neurologic findings during early adulthood.

Crigler-Najjar syndrome is a severe condition characterized by high levels of a toxic substance called bilirubin in the blood (hyperbilirubinemia). Bilirubin is produced when red blood cells are broken down. This substance is removed from the body only after it undergoes a chemical reaction in the liver, which converts the toxic form of bilirubin (called unconjugated bilirubin) to a nontoxic form called conjugated bilirubin. People with Crigler-Najjar syndrome have a buildup of unconjugated bilirubin in their blood (unconjugated hyperbilirubinemia).\n\nBilirubin has an orange-yellow tint, and hyperbilirubinemia causes yellowing of the skin and whites of the eyes (jaundice). In Crigler-Najjar syndrome, jaundice is apparent at birth or in infancy. Severe unconjugated hyperbilirubinemia can lead to a condition called kernicterus, which is a form of brain damage caused by the accumulation of unconjugated bilirubin in the brain and nerve tissues. Babies with kernicterus are often extremely tired (lethargic) and may have weak muscle tone (hypotonia). These babies may experience episodes of increased muscle tone (hypertonia) and arching of their backs. Kernicterus can lead to other neurological problems, including involuntary writhing movements of the body (choreoathetosis), hearing problems, or intellectual disability.\n\nCrigler-Najjar syndrome is divided into two types. Type 1 (CN1) is very severe, and affected individuals can die in childhood due to kernicterus, although with proper treatment, they may survive longer. Type 2 (CN2) is less severe. People with CN2 are less likely to develop kernicterus, and most affected individuals survive into adulthood.

Following dietary exposure to fructose, sucrose, or sorbitol, untreated hereditary fructose intolerance (HFI) is characterized by metabolic disturbances (hypoglycemia, lactic acidemia, hypophosphatemia, hyperuricemia, hypermagnesemia, hyperalaninemia) and clinical findings (nausea, vomiting, and abdominal distress; chronic growth restriction / failure to thrive). While untreated HFI typically first manifested when fructose- and sucrose-containing foods were introduced in the course of weaning young infants from breast milk, it is now presenting earlier, due to the addition of fructose-containing nutrients in infant formulas. If the infant ingests large quantities of fructose, the infant may acutely develop lethargy, seizures, and/or progressive coma. Untreated HFI may result in renal and hepatic failure. If identified and treated before permanent organ injury occurs, individuals with HFI can experience a normal quality of life and life expectancy.

The hereditary hyperbilirubinemias include (1) those resulting in predominantly unconjugated hyperbilirubinemia: Gilbert or Arias syndrome, Crigler-Najjar syndrome type I (218800), and Crigler-Najjar syndrome type II (606785); and (2) those resulting in predominantly conjugated hyperbilirubinemia: Dubin-Johnson syndrome (237500), Rotor syndrome (237450), and several forms of intrahepatic cholestasis (147480, 211600, 214950, 243300) (Wolkoff et al., 1983). Detailed studies show that patients with Gilbert syndrome have reduced activity of bilirubin glucuronosyltransferase (Bosma et al., 1995, Koiwai et al., 1995). Genetic Heterogeneity of Hyperbilirubinemia See also Crigler-Najjar syndrome type I (HBLRCN1; 218800), Crigler-Najjar syndrome type II (HBLRCN2; 606785), and transient familial neonatal hyperbilirubinemia (HBLRTFN; 237900), all caused by mutation in the UGT1A1 gene (191740) on chromosome 2q37; Dubin-Johnson syndrome (DJS, HBLRDJ; 237500), caused by mutation in the ABCC2 gene (601107) on chromosome 10q24; and Rotor syndrome (HBLRR; 237450), caused by digenic mutation in the SLCO1B1 (604843) and SLCOB3 (605495) genes, both on chromosome 12p.

Glycogen storage disease VII is an autosomal recessive metabolic disorder characterized clinically by exercise intolerance, muscle cramping, exertional myopathy, and compensated hemolysis. Myoglobinuria may also occur. The deficiency of the muscle isoform of PFK results in a total and partial loss of muscle and red cell PFK activity, respectively. Raben and Sherman (1995) noted that not all patients with GSD VII seek medical care because in some cases it is a relatively mild disorder.

Wilson disease is a disorder of copper metabolism that can present with hepatic, neurologic, or psychiatric disturbances, or a combination of these, in individuals ranging from age three years to older than 50 years; symptoms vary among and within families. Liver disease includes recurrent jaundice, simple acute self-limited hepatitis-like illness, autoimmune-type hepatitis, fulminant hepatic failure, or chronic liver disease. Neurologic presentations include movement disorders (tremors, poor coordination, loss of fine-motor control, chorea, choreoathetosis) or rigid dystonia (mask-like facies, rigidity, gait disturbance, pseudobulbar involvement). Psychiatric disturbance includes depression, neurotic behaviors, disorganization of personality, and, occasionally, intellectual deterioration. Kayser-Fleischer rings, frequently present, result from copper deposition in Descemet's membrane of the cornea and reflect a high degree of copper storage in the body.

Dubin-Johnson syndrome (DJS) is an autosomal recessive disorder characterized by conjugated hyperbilirubinemia, an increase in the urinary excretion of coproporphyrin isomer I, deposition of melanin-like pigment in hepatocytes, and prolonged retention of sulfobromophthalein, but otherwise normal liver function (summary by Wada et al., 1998).

A multifocal, multisystem form of Langerhans-cell histiocytosis. There is involvement of multiple organ systems including the bones, skin, liver, spleen, and lymph nodes. Patients are usually infants presenting with fever, hepatosplenomegaly, lymphadenopathy, bone and skin lesions, and pancytopenia.

Familial lipoprotein lipase (LPL) deficiency usually presents in childhood and is characterized by very severe hypertriglyceridemia with episodes of abdominal pain, recurrent acute pancreatitis, eruptive cutaneous xanthomata, and hepatosplenomegaly. Clearance of chylomicrons from the plasma is impaired, causing triglycerides to accumulate in plasma and the plasma to have a milky (lactescent or lipemic) appearance. Symptoms usually resolve with restriction of total dietary fat to =20 g/day.

A greater than normal number of blood cells in the reticuloendothelial system.

Congenital erythropoietic porphyria (CEP) is characterized in most individuals by severe cutaneous photosensitivity with blistering and increased friability of the skin over light-exposed areas. Onset in most affected individuals occurs at birth or early infancy. The first manifestation is often pink-to-dark red discoloration of the urine. Hemolytic anemia is common and can range from mild to severe, with some affected individuals requiring chronic blood transfusions. Porphyrin deposition may lead to corneal ulcers and scarring, reddish-brown discoloration of the teeth (erythrodontia), and bone loss and/or expansion of the bone marrow. The phenotypic spectrum, however, is broad and ranges from nonimmune hydrops fetalis in utero to late-onset disease with only mild cutaneous manifestations in adulthood.

Hereditary coproporphyria (HCP) is an acute (hepatic) porphyria in which the acute symptoms are neurovisceral and occur in discrete episodes. Attacks typically start in the abdomen with low-grade pain that slowly increases over a period of days (not hours) with nausea progressing to vomiting. In some individuals, the pain is predominantly in the back or extremities. When an acute attack is untreated, a motor neuropathy may develop over a period of days or a few weeks. The neuropathy first appears as weakness proximally in the arms and legs, then progresses distally to involve the hands and feet. Some individuals experience respiratory insufficiency due to loss of innervation of the diaphragm and muscles of respiration. Acute attacks are associated commonly with use of certain medications, caloric deprivation, and changes in female reproductive hormones. About 20% of those with an acute attack also experience photosensitivity associated with bullae and skin fragility.

POLG-related disorders comprise a continuum of overlapping phenotypes that were clinically defined long before their molecular basis was known. Most affected individuals have some, but not all, of the features of a given phenotype; nonetheless, the following nomenclature can assist the clinician in diagnosis and management. Onset of the POLG-related disorders ranges from infancy to late adulthood. Alpers-Huttenlocher syndrome (AHS), one of the most severe phenotypes, is characterized by childhood-onset progressive and ultimately severe encephalopathy with intractable epilepsy and hepatic failure. Childhood myocerebrohepatopathy spectrum (MCHS) presents between the first few months of life and about age three years with developmental delay or dementia, lactic acidosis, and a myopathy with failure to thrive. Other findings can include liver failure, renal tubular acidosis, pancreatitis, cyclic vomiting, and hearing loss. Myoclonic epilepsy myopathy sensory ataxia (MEMSA) now describes the spectrum of disorders with epilepsy, myopathy, and ataxia without ophthalmoplegia. MEMSA now includes the disorders previously described as spinocerebellar ataxia with epilepsy (SCAE). The ataxia neuropathy spectrum (ANS) includes the phenotypes previously referred to as mitochondrial recessive ataxia syndrome (MIRAS) and sensory ataxia neuropathy dysarthria and ophthalmoplegia (SANDO). About 90% of persons in the ANS have ataxia and neuropathy as core features. Approximately two thirds develop seizures and almost one half develop ophthalmoplegia; clinical myopathy is rare. Autosomal recessive progressive external ophthalmoplegia (arPEO) is characterized by progressive weakness of the extraocular eye muscles resulting in ptosis and ophthalmoparesis (or paresis of the extraocular muscles) without associated systemic involvement; however, caution is advised because many individuals with apparently isolated arPEO at the onset develop other manifestations of POLG-related disorders over years or decades. Of note, in the ANS spectrum the neuropathy commonly precedes the onset of PEO by years to decades. Autosomal dominant progressive external ophthalmoplegia (adPEO) typically includes a generalized myopathy and often variable degrees of sensorineural hearing loss, axonal neuropathy, ataxia, depression, parkinsonism, hypogonadism, and cataracts (in what has been called "chronic progressive external ophthalmoplegia plus," or "CPEO+").

Rotor syndrome is characterized by mild conjugated and unconjugated hyperbilirubinemia that usually begins shortly after birth or in childhood. Jaundice may be intermittent. Conjunctival icterus may be the only clinical manifestation.

The term "galactosemia" refers to disorders of galactose metabolism that include classic galactosemia, clinical variant galactosemia, and biochemical variant galactosemia (not covered in this chapter). This GeneReview focuses on: Classic galactosemia, which can result in life-threatening complications including feeding problems, failure to thrive, hepatocellular damage, bleeding, and E coli sepsis in untreated infants. If a lactose-restricted diet is provided during the first ten days of life, the neonatal signs usually quickly resolve and the complications of liver failure, sepsis, and neonatal death are prevented; however, despite adequate treatment from an early age, children with classic galactosemia remain at increased risk for developmental delays, speech problems (termed childhood apraxia of speech and dysarthria), and abnormalities of motor function. Almost all females with classic galactosemia manifest hypergonadatropic hypogonadism or premature ovarian insufficiency (POI). Clinical variant galactosemia, which can result in life-threatening complications including feeding problems, failure to thrive, hepatocellular damage including cirrhosis, and bleeding in untreated infants. This is exemplified by the disease that occurs in African Americans and native Africans in South Africa. Persons with clinical variant galactosemia may be missed with newborn screening as the hypergalactosemia is not as marked as in classic galactosemia and breath testing is normal. If a lactose-restricted diet is provided during the first ten days of life, the severe acute neonatal complications are usually prevented. African Americans with clinical variant galactosemia and adequate early treatment do not appear to be at risk for long-term complications, including POI.

Cholestasis-lymphedema syndrome is a rare genetic disorder characterized by neonatal intrahepatic cholestasis, often lessening and becoming intermittent with age, and severe chronic lymphedema which mainly affects the lower limbs. Patients often present with fat malabsorption leading to failure to thrive, fat soluble vitamin deficiency with bleeding, rickets, and neuropathy. In 25% of cases, cirrhosis occurs during childhood or later in life.

Hydroxykynureninuria, also known as xanthurenicaciduria, is an autosomal recessive condition characterized by high urinary excretion of kynurenine (KYN), xanthurenic acid (XA) and 3-hydroxykynurenine (3-OHKYN), with no detectable anthranilic acid (AA) or 3-hydroxyanthranilic acid (3-OHAA) (Christensen et al., 2007).

Multiple acyl-CoA dehydrogenase deficiency (MADD) represents a clinical spectrum in which presentations can be divided into type I (neonatal onset with congenital anomalies), type II (neonatal onset without congenital anomalies), and type III (late onset). Individuals with type I or II MADD typically become symptomatic in the neonatal period with severe metabolic acidosis, which may be accompanied by profound hypoglycemia and hyperammonemia. Many affected individuals die in the newborn period despite metabolic treatment. In those who survive the neonatal period, recurrent metabolic decompensation resembling Reye syndrome and the development of hypertrophic cardiomyopathy can occur. Congenital anomalies may include dysmorphic facial features, large cystic kidneys, hypospadias and chordee in males, and neuronal migration defects (heterotopias) on brain MRI. Individuals with type III MADD, the most common presentation, can present from infancy to adulthood. The most common symptoms are muscle weakness, exercise intolerance, and/or muscle pain, although metabolic decompensation with episodes of rhabdomyolysis can also be seen. Rarely, individuals with late-onset MADD (type III) may develop severe sensory neuropathy in addition to proximal myopathy.

A rare genetic hepatic disease characterized by very high serum bilirubin levels in a newborn, clinically presenting as jaundice during the first few days of life. The condition is usually self-resolving, although in some cases it can lead to kernicterus with corresponding symptoms (including lethargy, high-pitched crying, hypotonia, missing reflexes, vomiting, or seizures, among others), which may result in chronic disability and even death.

Aldolase A deficiency is an autosomal recessive disorder associated with hereditary hemolytic anemia (Kishi et al., 1987).

Red cell pyruvate kinase deficiency, or congenital nonspherocytic hemolyic anemia-2 (CNSHA2), is the most common cause of hereditary nonspherocytic hemolytic anemia. PK deficiency is also the most frequent enzyme abnormality of the glycolytic pathway (Zanella et al., 2005).

Congenital isolated adrenocorticotropic hormone deficiency (IAD) is characterized by severe hypoglycemia in the neonatal period, associated with seizures in about half of cases, prolonged cholestatic jaundice, and very low plasma ACTH levels with no significant response to corticotropin-releasing hormone (CRH; 122560). Plasma cortisol levels are also extremely low (Vallette-Kasic et al., 2005). TBX19 is required for initiation of transcription of the POMC gene (176830), which produces the precursor peptide from which ACTH is derived (Lamolet et al., 2001).

An autoimmune disorder characterized by the association of primary biliary cirrhosis with limited cutaneous systemic sclerosis. Onset occurs between 30-65 years. Occurs sporadically, but rare familial cases with an unknown inheritance pattern have been observed. There is no cure and management is mainly supportive.

Epimerase deficiency galactosemia (GALE deficiency galactosemia) is generally considered a continuum comprising several forms: Generalized. Enzyme activity is profoundly decreased in all tissues tested. Peripheral. Enzyme activity is deficient in red blood cells (RBC) and circulating white blood cells, but normal or near normal in all other tissues. Intermediate. Enzyme activity is deficient in red blood cells and circulating white blood cells and less than 50% of normal levels in other cells tested. Infants with generalized epimerase deficiency galactosemia develop clinical findings on a regular milk diet (which contains lactose, a disaccharide of galactose and glucose); manifestations include hypotonia, poor feeding, vomiting, weight loss, jaundice, hepatomegaly, liver dysfunction, aminoaciduria, and cataracts. Prompt removal of galactose/lactose from their diet resolves or prevents these acute symptoms. Longer-term features that may be seen in those with generalized epimerase deficiency include short stature, developmental delay, sensorineural hearing loss, and skeletal anomalies. In contrast, neonates with the peripheral or intermediate form generally remain clinically well even on a regular milk diet and are usually only identified by biochemical testing, often in newborn screening programs.

A rare genetic lethal multiple congenital anomalies/dysmorphic syndrome characterized by consistently abnormal facial appearance, true or apparent hydrocephalus, motor and cognitive developmental delay, failure to thrive (feeding difficulties, vomiting, chest infections) and death within a few months of birth. Carp mouth, hairiness of the forehead, neonatal hyperbilirubinemia and advanced bone age may also be associated. There have been no further descriptions in the literature since 1991.

MED12-related disorders include the phenotypes of FG syndrome type 1 (FGS1), Lujan syndrome (LS), X-linked Ohdo syndrome (XLOS), Hardikar syndrome (HS), and nonspecific intellectual disability (NSID). FGS1 and LS share the clinical findings of cognitive impairment, hypotonia, and abnormalities of the corpus callosum. FGS1 is further characterized by absolute or relative macrocephaly, tall forehead, downslanted palpebral fissures, small and simple ears, constipation and/or anal anomalies, broad thumbs and halluces, and characteristic behavior. LS is further characterized by large head, tall thin body habitus, long thin face, prominent nasal bridge, high narrow palate, and short philtrum. Carrier females in families with FGS1 and LS are typically unaffected. XLOS is characterized by intellectual disability, blepharophimosis, and facial coarsening. HS has been described in females with cleft lip and/or cleft palate, biliary and liver anomalies, intestinal malrotation, pigmentary retinopathy, and coarctation of the aorta. Developmental and cognitive concerns have not been reported in females with HS. Pathogenic variants in MED12 have been reported in an increasing number of males and females with NSID, with affected individuals often having clinical features identified in other MED12-related disorders.

Hereditary thrombotic thrombocytopenic purpura (TTP), also known as Upshaw-Schulman syndrome (USS), is a rare autosomal recessive thrombotic microangiopathy (TMA). Clinically, acute phases of TTP are defined by microangiopathic mechanical hemolytic anemia, severe thrombocytopenia, and visceral ischemia. Hereditary TTP makes up 5% of TTP cases and is caused mostly by biallelic mutation in the ADAMTS13 gene, or in very rare cases, by monoallelic ADAMTS13 mutation associated with a cluster of single-nucleotide polymorphisms (SNPs); most cases of all TTP (95%) are acquired via an autoimmune mechanism (see 188030). Hereditary TTP is more frequent among child-onset TTP compared with adult-onset TTP, and its clinical presentation is significantly different as a function of its age of onset. Child-onset TTP usually starts in the neonatal period with hematological features and severe jaundice. In contrast, almost all cases of adult-onset hereditary TTP are unmasked during the first pregnancy of a woman whose disease was silent during childhood (summary by Joly et al., 2018).

Congenital dyserythropoietic anemia type II (CDA II) is the most common form of CDA (see this term) characterized by anemia, jaundice and splenomegaly and often leading to liver iron overload and gallstones.

Stomatin-deficient cryohydrocytosis with neurologic defects (SDCHCN) is an autosomal dominant disorder characterized by delayed psychomotor development, seizures, cataracts, and pseudohyperkalemia resulting from defects in the red blood cell membrane. The disorder combines the neurologic features of Glut1 deficiency syndrome-1 (GLUT1DS1; 606777), resulting from impaired glucose transport at the blood-brain barrier, and hemolytic anemia/pseudohyperkalemia with stomatocytosis, resulting from a cation leak in erythrocytes (summary by Bawazir et al., 2012). For a discussion of clinical and genetic heterogeneity of red cell stomatocyte disorders, see 194380.

Congenital defects of bile acid synthesis are autosomal recessive disorders characterized by neonatal onset of progressive liver disease with cholestatic jaundice and malabsorption of lipids and lipid-soluble vitamins from the gastrointestinal tract resulting from a primary failure to synthesize bile acids. Affected infants show failure to thrive and secondary coagulopathy. In most forms of the disorder, there is a favorable response to oral bile acid therapy (summary by Cheng et al., 2003). Genetic Heterogeneity of Congenital Defects in Bile Acid Synthesis There are several disorders that result from defects in bile acid synthesis. See CBAS2 (235555), caused by mutation in the delta(4)-3-oxosteroid 5-beta-reductase gene (AKR1D1; 604741) on chromosome 7q33; CBAS3 (613812), caused by mutation in the 7-alpha hydroxylase gene (CYP7B1; 603711) on chromosome 8q12; CBAS4 (214950), caused by mutation in the AMACR gene (604489) on chromosome 5p13; CBAS5 (616278), caused by mutation in the ABCD3 gene (170995) on chromosome 1p21; and CBAS6 (617308), caused by mutation in the ACOX2 gene (601641) on chromosome 3p14. See also progressive familial intrahepatic cholestasis (PFIC1; 211600), which has a similar phenotype.

Ichthyosis, leukocyte vacuoles, alopecia, and sclerosing cholangitis (ILVASC) is a rare autosomal recessive syndrome characterized by scalp hypotrichosis, scarring alopecia, ichthyosis, and sclerosing cholangitis (summary by Feldmeyer et al., 2006).

Niemann-Pick disease type C (NPC) is a slowly progressive lysosomal disorder whose principal manifestations are age dependent. The manifestations in the perinatal period and infancy are predominantly visceral, with hepatosplenomegaly, jaundice, and (in some instances) pulmonary infiltrates. From late infancy onward, the presentation is dominated by neurologic manifestations. The youngest children may present with hypotonia and developmental delay, with the subsequent emergence of ataxia, dysarthria, dysphagia, and, in some individuals, epileptic seizures, dystonia, and gelastic cataplexy. Although cognitive impairment may be subtle at first, it eventually becomes apparent that affected individuals have a progressive dementia. Older teenagers and young adults may present predominantly with apparent early-onset dementia or psychiatric manifestations; however, careful examination usually identifies typical neurologic signs.

The RH-null phenotype designates rare individuals whose red blood cells lack all Rh antigens. Two RH-null types, the regulator type (RHNR) and the amorph type (RHNA; 617970), arising from independent genetic mechanisms have been distinguished. The regulator type is caused by mutation in the RHAG gene (180297), which encodes the Rh50 glycoprotein that is crucial for the surface disposition of Rh antigens. The amorph type arises from mutations at the RH locus itself that silence Rh expression. The RH locus contains the RHD (111680) and RHCE (111700) genes tandemly arranged at chromosome 1p36-p34. Four genes must therefore be silenced to produce the RH-null phenotype. The absence of the D antigen, produced by the RHD gene, is common in the human population; the D-negative phenotype may result from deletion or genetic alteration of the RHD gene. The absence of D antigen defines the Rh-negative status of the human erythrocyte (summary by Huang et al., 2000). Whereas Rh-null cells lack all Rh antigens, Rh-mod cells display a markedly reduced antigen expression. Clinically, Rh-deficient individuals exhibit a mild to moderate chronic hemolytic anemia accompanied by a varying degree of spherostomatocytosis (summary by Huang et al., 1999).

MPV17-related mitochondrial DNA (mtDNA) maintenance defect presents in the vast majority of affected individuals as an early-onset encephalohepatopathic (hepatocerebral) disease that is typically associated with mtDNA depletion, particularly in the liver. A later-onset neuromyopathic disease characterized by myopathy and neuropathy, and associated with multiple mtDNA deletions in muscle, has also rarely been described. MPV17-related mtDNA maintenance defect, encephalohepatopathic form is characterized by: Hepatic manifestations (liver dysfunction that typically progresses to liver failure, cholestasis, hepatomegaly, and steatosis); Neurologic involvement (developmental delay, hypotonia, microcephaly, and motor and sensory peripheral neuropathy); Gastrointestinal manifestations (gastrointestinal dysmotility, feeding difficulties, and failure to thrive); and Metabolic derangements (lactic acidosis and hypoglycemia). Less frequent manifestations include renal tubulopathy, nephrocalcinosis, and hypoparathyroidism. Progressive liver disease often leads to death in infancy or early childhood. Hepatocellular carcinoma has been reported.

Disorders of intracellular cobalamin metabolism have a variable phenotype and age of onset that are influenced by the severity and location within the pathway of the defect. The prototype and best understood phenotype is cblC; it is also the most common of these disorders. The age of initial presentation of cblC spans a wide range: In utero with fetal presentation of nonimmune hydrops, cardiomyopathy, and intrauterine growth restriction. Newborns, who can have microcephaly, poor feeding, and encephalopathy. Infants, who can have poor feeding and slow growth, neurologic abnormality, and, rarely, hemolytic uremic syndrome (HUS). Toddlers, who can have poor growth, progressive microcephaly, cytopenias (including megaloblastic anemia), global developmental delay, encephalopathy, and neurologic signs such as hypotonia and seizures. Adolescents and adults, who can have neuropsychiatric symptoms, progressive cognitive decline, thromboembolic complications, and/or subacute combined degeneration of the spinal cord.

A very rare syndrome described in four siblings of one French family and with characteristics of branchial dysplasia (malar hypoplasia, macrostomia, preauricular tags and meatal atresia), club feet, inguinal hernia and cholestasis due to paucity of interlobular bile ducts and intellectual deficit.

Congenital bile acid synthesis defect type 2 is a disorder characterized by cholestasis, a condition that impairs the production and release of a digestive fluid called bile from liver cells. Bile is used during digestion to absorb fats and fat-soluble vitamins, such as vitamins A, D, E, and K. People with congenital bile acid synthesis defect type 2 cannot produce (synthesize) bile acids, which are a component of bile that stimulate bile flow and help it absorb fats and fat-soluble vitamins. As a result, an abnormal form of bile is produced.\n\nThe signs and symptoms of congenital bile acid synthesis defect type 2 often develop in infancy. Affected infants usually have a failure to gain weight and grow at the expected rate (failure to thrive) and yellowing of the skin and eyes (jaundice) due to impaired bile flow and a buildup of partially formed bile. Excess fat in the feces (steatorrhea) is another feature of congenital bile acid synthesis defect type 2. As the condition progresses, affected individuals can develop liver abnormalities including inflammation or chronic liver disease (cirrhosis). Some individuals with congenital bile acid synthesis defect type 2 cannot absorb certain fat-soluble vitamins, which can result in softening and weakening of the bones (rickets) or problems with blood clotting that lead to prolonged bleeding.\n\nIf left untreated, congenital bile acid synthesis defect type 2 typically leads to cirrhosis and death in childhood.

Any arthrogryposis-renal dysfunction-cholestasis syndrome in which the cause of the disease is a mutation in the VPS33B gene.

Triosephosphate isomerase deficiency (TPID) is an autosomal recessive multisystem disorder characterized by congenital hemolytic anemia, and progressive neuromuscular dysfunction beginning in early childhood. Many patients die from respiratory failure in childhood. The neurologic syndrome is variable, but usually includes lower motor neuron dysfunction with hypotonia, muscle weakness and atrophy, and hyporeflexia. Some patients may show additional signs such as dystonic posturing and/or spasticity. Laboratory studies show intracellular accumulation of dihydroxyacetone phosphate (DHAP), particularly in red blood cells (summary by Fermo et al., 2010).

Overhydrated hereditary stomatocytosis is a variably compensated macrocytic hemolytic anemia of fluctuating severity, characterized by circulating erythrocytes with slit-like lucencies (stomata) evident on peripheral blood smears. OHST red cells exhibit cation leak, resulting in elevated cell Na+ content with reduced K+ content, with increased ouabain-resistant cation leak fluxes in the presence of presumably compensatory increases in ouabain-sensitive Na(+)-K(+) ATPase activity, and red cell age-dependent loss of stomatin/EBP7.2 (EBP72; 133090) from the erythroid membrane. Clinically, patients with OHST exhibit overhydrated erythrocytes and a temperature-dependent red cell cation leak. The temperature dependence of the leak is 'monotonic' and has a steep slope, reflecting the very large leak at 37 degrees centigrade (summary by Bruce, 2009 and Stewart et al., 2011). For a discussion of clinical and genetic heterogeneity of the hereditary stomatocytoses, see 194380.

Cirrhosis in which no causative agent can be identified.

Familial hemophagocytic lymphohistiocytosis-2 (FHL2) is an autosomal recessive disorder of immune dysregulation with onset in infancy or early childhood. It is characterized clinically by fever, edema, hepatosplenomegaly, and liver dysfunction. Neurologic impairment, seizures, and ataxia are frequent. Laboratory studies show pancytopenia, coagulation abnormalities, hypofibrinogenemia, and hypertriglyceridemia. There is increased production of cytokines, such as gamma-interferon (IFNG; 147570) and TNF-alpha (191160), by hyperactivation and proliferation of T cells and macrophages. Activity of cytotoxic T cells and NK cells is reduced, consistent with a defect in cellular cytotoxicity. Bone marrow, lymph nodes, spleen, and liver show features of hemophagocytosis. Chemotherapy and/or immunosuppressant therapy may result in symptomatic remission, but the disorder is fatal without bone marrow transplantation (summary by Dufourcq-Lagelouse et al., 1999, Stepp et al., 1999, and Molleran Lee et al., 2004). For a general phenotypic description and a discussion of genetic heterogeneity of FHL, see 267700.

Hemophagocytic lymphohistiocytosis is a hyperinflammatory disorder clinically diagnosed based on the fulfillment of 5 of 8 criteria, including fever, splenomegaly, bicytopenia, hypertriglyceridemia and/or hypofibrinogenemia, hemophagocytosis, low or absent natural killer (NK) cell activity, hyperferritinemia, and high soluble IL2 receptor levels (IL2R; 147730). The disorder typically presents in infancy or early childhood. Persistent remission is rarely achieved with chemo- or immunotherapy; hematopoietic stem cell transplantation is the only cure (summary by Muller et al., 2014). For a phenotypic description and a discussion of genetic heterogeneity of familial hemophagocytic lymphohistiocytosis (FHL), see 267700.

The signs and symptoms of PFIC2 are typically related to liver disease only; however, these signs and symptoms tend to be more severe than those experienced by people with PFIC1. People with PFIC2 often develop liver failure within the first few years of life. Additionally, affected individuals are at increased risk of developing a type of liver cancer called hepatocellular carcinoma.\n\nIn addition to signs and symptoms related to liver disease, people with PFIC1 may have short stature, deafness, diarrhea, inflammation of the pancreas (pancreatitis), and low levels of fat-soluble vitamins (vitamins A, D, E, and K) in the blood. Affected individuals typically develop liver failure before adulthood.\n\nThere are three known types of PFIC: PFIC1, PFIC2, and PFIC3. The types are also sometimes described as shortages of particular proteins needed for normal liver function. Each type has a different genetic cause.\n\nSigns and symptoms of PFIC typically begin in infancy and are related to bile buildup and liver disease. Specifically, affected individuals experience severe itching, yellowing of the skin and whites of the eyes (jaundice), failure to gain weight and grow at the expected rate (failure to thrive), high blood pressure in the vein that supplies blood to the liver (portal hypertension), and an enlarged liver and spleen (hepatosplenomegaly).\n\nMost people with PFIC3 have signs and symptoms related to liver disease only. Signs and symptoms of PFIC3 usually do not appear until later in infancy or early childhood; rarely, people are diagnosed in early adulthood. Liver failure can occur in childhood or adulthood in people with PFIC3.\n\nProgressive familial intrahepatic cholestasis (PFIC) is a disorder that causes progressive liver disease, which typically leads to liver failure. In people with PFIC, liver cells are less able to secrete a digestive fluid called bile. The buildup of bile in liver cells causes liver disease in affected individuals.

The phenotypic spectrum of ATP8B1 deficiency ranges from severe through moderate to mild. Severe ATP8B1 deficiency is characterized by infantile-onset cholestasis that progresses to cirrhosis, hepatic failure, and early death. Although mild-to-moderate ATP8B1 deficiency initially was thought to involve intermittent symptomatic cholestasis with a lack of hepatic fibrosis, it is now known that hepatic fibrosis may be present early in the disease course. Furthermore, in some persons with ATP8B1 deficiency the clinical findings can span the phenotypic spectrum, shifting over time from the mild end of the spectrum (episodic cholestasis) to the severe end of the spectrum (persistent cholestasis). Sensorineural hearing loss (SNHL) is common across the phenotypic spectrum.

In general, gallbladder disease (GBD) is one of the major digestive diseases. GBD prevalence is particularly high in some minority populations in the United States, including Native and Mexican Americans. Gallstones composed of cholesterol (cholelithiasis) are the common manifestations of GBD in western countries, including the United States. Most people with gallstones remain asymptomatic through their lifetimes; however, it is estimated that approximately 10 to 50% of individuals eventually develop symptoms. Significant risk factors associated with GBD are age, female sex, obesity (especially central obesity), lipids, diet, parity, type 2 diabetes (125853), medications, and Mexican American ethnicity. GBD appears to be strongly related to the metabolic syndrome (605552) and/or its major components, such as hyperinsulinism, dyslipidemia, and abdominal adiposity (Boland et al., 2002; Tsai et al., 2004). Infection, specifically by Helicobacter, has been implicated in cholelithiasis and cholecystitis (Silva et al., 2003; Maurer et al., 2005). Low phospholipid-associated cholelithiasis is a specific form of gallbladder disease characterized by young-adult onset of chronic cholestasis with intrahepatic sludge and cholesterol cholelithiasis. Affected individuals have recurrence of the disorder after cholecystectomy and show a favorable response to treatment with ursodeoxycholic acid (UDCA) (summary by Pasmant et al., 2012). Mutation in the ABCB4 gene can cause a spectrum of related diseases, including the more severe progressive familial intrahepatic cholestasis-3 (PFIC3; 602347), intrahepatic cholestasis of pregnancy-3 (ICP3; 614972), andoral contraceptive-induced cholestasis (OCIC; see 614972). Genetic Heterogeneity of Gallbladder Disease Two major susceptibility loci for symptomatic gallbladder disease have been identified on chromosome 1p in Mexican Americans (GBD2, 609918; GBD3, 609919). In addition, variations in the ABCG8 gene (605460) on chromosome 2p21 confer susceptibility to gallbladder disease (GBD4; 611465).

Any hereditary spherocytosis in which the cause of the disease is a mutation in the ANK1 gene.

People with the mild form may have very mild anemia or sometimes have no symptoms. People with the moderate form typically have anemia, jaundice, and splenomegaly. Many also develop gallstones. The signs and symptoms of moderate hereditary spherocytosis usually appear in childhood. Individuals with the moderate/severe form have all the features of the moderate form but also have severe anemia. Those with the severe form have life-threatening anemia that requires frequent blood transfusions to replenish their red blood cell supply. They also have severe splenomegaly, jaundice, and a high risk for developing gallstones. Some individuals with the severe form have short stature, delayed sexual development, and skeletal abnormalities.\n\nThere are four forms of hereditary spherocytosis, which are distinguished by the severity of signs and symptoms. They are known as the mild form, the moderate form, the moderate/severe form, and the severe form. It is estimated that 20 to 30 percent of people with hereditary spherocytosis have the mild form, 60 to 70 percent have the moderate form, 10 percent have the moderate/severe form, and 3 to 5 percent have the severe form.\n\nHereditary spherocytosis is a condition that affects red blood cells. People with this condition typically experience a shortage of red blood cells (anemia), yellowing of the eyes and skin (jaundice), and an enlarged spleen (splenomegaly). Most newborns with hereditary spherocytosis have severe anemia, although it improves after the first year of life. Splenomegaly can occur anytime from early childhood to adulthood. About half of affected individuals develop hard deposits in the gallbladder called gallstones, which typically occur from late childhood to mid-adulthood.

This syndrome is characterized by exocrine pancreatic insufficiency, dyserythropoietic anemia, and calvarial hyperostosis. It has been described in four children, three boys and one girl, from two consanguineous families. The disease is due to a mutation in the COX4I2 gene, encoding a mitochondrial cytochrome C oxidase sub-unit. Transmission is autosomal recessive.

EPB42-related hereditary spherocytosis (EPB42-HS) is a chronic nonimmune hemolytic anemia that is usually of mild-to-moderate severity. EPB42-HS can present with jaundice as early as the first 24 hours of life or can present later in childhood with anemia resulting from a hemolytic crisis or aplastic crisis (usually associated with a viral infection). In addition to the hematologic manifestations, serious complications include splenomegaly, which can become evident in early childhood, and cholelithiasis, which usually becomes evident in the second or third decade of life. Typical laboratory findings in EPB42-HS include anemia (decreased hemoglobin [Hgb] level) and reticulocytosis (increased percentage of reticulocytes), with high mean corpuscular Hgb concentration, presence of spherocytes in the peripheral blood smear, significantly decreased or absent haptoglobin, mildly increased osmotic fragility in osmotic fragility assay, increased Omin (osmolality at which 50% of red blood cells hemolyze), and decreased maximal elongation index (EImax) in osmotic gradient ektacytometry.

People with the mild form may have very mild anemia or sometimes have no symptoms. People with the moderate form typically have anemia, jaundice, and splenomegaly. Many also develop gallstones. The signs and symptoms of moderate hereditary spherocytosis usually appear in childhood. Individuals with the moderate/severe form have all the features of the moderate form but also have severe anemia. Those with the severe form have life-threatening anemia that requires frequent blood transfusions to replenish their red blood cell supply. They also have severe splenomegaly, jaundice, and a high risk for developing gallstones. Some individuals with the severe form have short stature, delayed sexual development, and skeletal abnormalities.\n\nThere are four forms of hereditary spherocytosis, which are distinguished by the severity of signs and symptoms. They are known as the mild form, the moderate form, the moderate/severe form, and the severe form. It is estimated that 20 to 30 percent of people with hereditary spherocytosis have the mild form, 60 to 70 percent have the moderate form, 10 percent have the moderate/severe form, and 3 to 5 percent have the severe form.\n\nHereditary spherocytosis is a condition that affects red blood cells. People with this condition typically experience a shortage of red blood cells (anemia), yellowing of the eyes and skin (jaundice), and an enlarged spleen (splenomegaly). Most newborns with hereditary spherocytosis have severe anemia, although it improves after the first year of life. Splenomegaly can occur anytime from early childhood to adulthood. About half of affected individuals develop hard deposits in the gallbladder called gallstones, which typically occur from late childhood to mid-adulthood.

Elliptocytosis is a hematologic disorder characterized by elliptically shaped erythrocytes and a variable degree of hemolytic anemia. Usually inherited as an autosomal dominant trait, elliptocytosis results from mutation in any one of several genes encoding proteins of the red cell membrane skeleton (summary by McGuire et al., 1988). Genetic Heterogeneity of Elliptocytosis Elliptocytosis-2 (130600) is caused by mutation in the SPTA1 gene (182860). Elliptocytosis-3 (617948) is caused by mutation in the SPTB gene (182870). Elliptocytosis-4 (166900), also known as Southeast Asian ovalocytosis, is caused by mutation in the SLC4A1 gene (109270). Also see pyropoikilocytosis (266140). See Delaunay (2007) for a discussion of the molecular basis of hereditary red cell membrane disorders.

Congenital nonspherocytic hemolytic anemia-1 (CNSHA1), caused by mutation in the G6PD gene, is the most common genetic form of chronic and drug-, food-, or infection-induced hemolytic anemia. G6PD catalyzes the first reaction in the pentose phosphate pathway, which is the only NADPH-generation process in mature red cells; therefore, defense against oxidative damage is dependent on G6PD. Most G6PD-deficient patients are asymptomatic throughout their life, but G6PD deficiency can be life-threatening. The most common clinical manifestations of G6PD deficiency are neonatal jaundice and acute hemolytic anemia, which in most patients is triggered by an exogenous agent, e.g., primaquine or fava beans. Acute hemolysis is characterized by fatigue, back pain, anemia, and jaundice. Increased unconjugated bilirubin, lactate dehydrogenase, and reticulocytosis are markers of the disorder. The striking similarity between the areas where G6PD deficiency is common and Plasmodium falciparum malaria (see 611162) is endemic provided evidence that G6PD deficiency confers resistance against malaria (summary by Cappellini and Fiorelli, 2008).

Autosomal dominant polycystic kidney disease (ADPKD) is generally a late-onset multisystem disorder characterized by bilateral kidney cysts, liver cysts, and an increased risk of intracranial aneurysms. Other manifestations include: cysts in the pancreas, seminal vesicles, and arachnoid membrane; dilatation of the aortic root and dissection of the thoracic aorta; mitral valve prolapse; and abdominal wall hernias. Kidney manifestations include early-onset hypertension, kidney pain, and kidney insufficiency. Approximately 50% of individuals with ADPKD have end-stage kidney disease (ESKD) by age 60 years. The prevalence of liver cysts increases with age and occasionally results in clinically significant severe polycystic liver disease (PLD), most often in females. Overall, the prevalence of intracranial aneurysms is fivefold higher than in the general population and further increased in those with a positive family history of aneurysms or subarachnoid hemorrhage. There is substantial variability in the severity of kidney disease and other extra-kidney manifestations.

Combined pituitary hormone deficiency (CPHD) in man denotes impaired production of growth hormone (GH; 139250) and one or more of the other 5 anterior pituitary hormones. Mutations of the POU1F1 gene in the human and Pit1 in the mouse are responsible for pleiotropic deficiencies of GH, prolactin (PRL; 176760), and thyroid-stimulating hormone (TSH; see 188540), while the production of adrenocorticotrophic hormone (ACTH; see 176830), luteinizing hormone (LH; 152780), and follicle-stimulating hormone (FSH; 136530) are preserved (Wu et al., 1998). Some patients exhibit only GH deficiency, although approximately 50% of isolated GH deficiency progresses to CPHD (Gergics et al., 2021). In infancy severe growth deficiency from birth as well as distinctive facial features with prominent forehead, marked midfacial hypoplasia with depressed nasal bridge, deep-set eyes, and a short nose with anteverted nostrils and hypoplastic pituitary gland by MRI examination can be seen (Aarskog et al., 1997). Some cases present with severe mental retardation along with short stature (Radovick et al., 1992). Reviews Voss and Rosenfeld (1992) reviewed the development and differentiation of the 5 pituitary cell types: galactotropes, gonadotropes, corticotropes, thyrotropes, and somatotropes. As indicated by the mutations in PIT1 described later, combined pituitary hormone deficiency can have either autosomal dominant or autosomal recessive inheritance, depending on the part of the PIT1 molecule affected by the mutation. Some mutations have a dominant-negative effect. Genetic Heterogeneity of Combined Pituitary Hormone Deficiency CPHD2 (262600), associated with hypogonadism, is caused by mutation in the PROP1 gene (601538). CPHD3 (221750), which is associated with rigid cervical spine and variable sensorineural deafness, is caused by mutation in the LHX3 gene (600577). CPHD4 (262700) is caused by mutation in the LHX4 gene (602146). CPHD5 (see septooptic dysplasia, 182230) is caused by mutation in the HESX1 gene (601802). CPHD6 (613986) is caused by mutation in the OTX2 gene (600037). CPHD7 (618160) is caused by mutation in the RNPC3 gene (618016). CPHD8 (620303) is caused by mutation in the ROBO1 gene (602430).

Like all CDGs, which are caused by a shortage of precursor monosaccharide phosphate or deficiencies in the glycosyltransferases required for lipid-linked oligosaccharide precursor (LLO) synthesis, CDG Ij is caused by a defect in the formation of DPAGT1, the first dolichyl-linked intermediate of the protein N-glycosylation pathway. For a general discussion of CDGs, see CDG1A (212065).

CDG IIe is caused by a mutation that impairs the integrity of the conserved oligomeric Golgi (COG) complex and alters Golgi trafficking, resulting in the disruption of multiple glycosylation pathways. For a general discussion of CDGs, see CDG1A (212065).

The hereditary hyperbilirubinemias include (1) those resulting in predominantly unconjugated hyperbilirubinemia: Gilbert or Arias syndrome, Crigler-Najjar syndrome type I, and Crigler-Najjar syndrome type II; and (2) those resulting in predominantly conjugated hyperbilirubinemia: Dubin-Johnson syndrome (237500), Rotor syndrome (237450), and several forms of intrahepatic cholestasis (147480, 211600, 214950, 243300) (Wolkoff et al., 1983). Detailed studies show that patients with Crigler-Najjar syndrome type II have reduced activity of bilirubin glucuronosyltransferase (Labrune et al., 1989, Seppen et al., 1994).

Nonspherocytic haemolytic anaemia due to hexokinase deficiency is characterised by severe hemolysis, appearing in infancy. Seventeen affected families have been reported so far. Transmission is autosomal recessive. Mutations have been described in <i>HK1</i>, the gene that encodes red blood cell-specific hexokinase-R.

Arthrogryposis, renal dysfunction, and cholestasis-2 (ARCS2) is a multisystem disorder associated with abnormalities in polarized liver and kidney cells (Qiu et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of ARCS, see ARCS1 (208085).

Glucose phosphate isomerase (GPI) deficiency is an inherited disorder that affects red blood cells, which carry oxygen to the body's tissues. People with this disorder have a condition known as chronic hemolytic anemia, in which red blood cells are broken down (undergo hemolysis) prematurely, resulting in a shortage of red blood cells (anemia). Chronic hemolytic anemia can lead to unusually pale skin (pallor), yellowing of the eyes and skin (jaundice), extreme tiredness (fatigue), shortness of breath (dyspnea), and a rapid heart rate (tachycardia). An enlarged spleen (splenomegaly), an excess of iron in the blood, and small pebble-like deposits in the gallbladder or bile ducts (gallstones) may also occur in this disorder.\n\nHemolytic anemia in GPI deficiency can range from mild to severe. In the most severe cases, affected individuals do not survive to birth. Individuals with milder disease can survive into adulthood. People with any level of severity of the disorder can have episodes of more severe hemolysis, called hemolytic crises, which can be triggered by bacterial or viral infections.\n\nA small percentage of individuals with GPI deficiency also have neurological problems, including intellectual disability and difficulty with coordinating movements (ataxia).

Congenital bile acid synthesis defect-3 (CBAS3) is an autosomal recessive disorder characterized by prolonged jaundice after birth, hepatomegaly, conjugated hyperbilirubinemia, elevations in characteristic abnormal bile acids, and progressive intrahepatic cholestasis with liver fibrosis (summary by Setchell et al., 1998 and Ueki et al., 2008). For a general phenotypic description and a discussion of genetic heterogeneity of congenital bile acid synthesis defects, see 607765.

Dihydrofolate reductase deficiency is an autosomal recessive metabolic disorder characterized by the hematologic findings of megaloblastic anemia and variable neurologic symptoms, ranging from severe developmental delay and generalized seizures in infancy (Banka et al., 2011) to childhood absence epilepsy with learning difficulties to lack of symptoms (Cario et al., 2011). Treatment with folinic acid can ameliorate some of the symptoms.

Neonatal cyanosis is characterized by symptoms in the fetus and neonate that gradually abate by 5 to 6 months of age. The disorder is caused by a defect in the fetal hemoglobin chain, which causes reduced affinity for oxygen due to steric inhibition of oxygen binding and/or due to increased oxidation of the fetal hemoglobin molecule to methemoglobin (Hb FM), which has decreased oxygen-binding capacity. Some patients develop anemia resulting from increased destruction of red cells containing abnormal or unstable hemoglobin. The cyanosis resolves spontaneously by 5 to 6 months of age or earlier, as the adult beta-globin chain (HBB; 141900) is produced and replaces the fetal gamma-globin chain (summary by Crowley et al., 2011).

Ogden syndrome (OGDNS) is an X-linked neurodevelopmental disorder characterized by postnatal growth failure, severely delayed psychomotor development, variable dysmorphic features, and hypotonia. Many patients also have cardiac malformations or arrhythmias (summary by Popp et al., 2015).

Acute infantile liver failure resulting from TRMU mutation is a transient disorder of hepatic function. In addition to elevated liver enzymes, jaundice, vomiting, coagulopathy, and hyperbilirubinemia, the presence of increased serum lactate is consistent with a defect in mitochondrial respiratory function. With supportive care, patients who survive the initial acute episode can recover and show normal development (Zeharia et al., 2009). See also transient infantile mitochondrial myopathy (MMIT; 500009), which is a similar disorder. A more severe, permanent disorder with some overlapping features is associated with mitochondrial DNA depletion (251880). See ILFS1 (615438) for information on syndromic infantile liver failure.

Primary microcephaly-epilepsy-permanent neonatal diabetes syndrome is a rare, genetic, neurologic disease characterized by congenital microcephaly, severe, early-onset epileptic encephalopathy (manifesting as intractable, myoclonic and/or tonic-clonic seizures), permanent, neonatal, insulin-dependent diabetes mellitus, and severe global developmental delay. Muscular hypotonia, skeletal abnormalities, feeding difficulties, and dysmorphic facial features (including narrow forehead, anteverted nares, small mouth with deep philtrum, tented upper lip vermilion) are frequently associated. Brain MRI reveals cerebral atrophy with cortical gyral simplification and aplasia/hypoplasia of the corpus callosum.

Intrahepatic cholestasis of pregnancy is a reversible form of cholestasis that occurs most often in the third trimester of pregnancy and recurs in 45 to 70% of subsequent pregnancies. Symptoms include pruritus, jaundice, increased serum bile salts, and abnormal liver enzymes, all of which resolve rapidly after delivery. However, the condition is associated with fetal complications, including placental insufficiency, premature labor, fetal distress, and intrauterine death. Some women with ICP may also be susceptible to oral contraceptive-induced cholestasis (OCIC) (summary by Pasmant et al., 2012). Genetic Heterogeneity of Intrahepatic Cholestasis of Pregnancy See also ICP3 (614972), caused by mutation in the ABCB4 gene (171060).

The peroxisome biogenesis disorder (PBD) Zellweger syndrome (ZS) is an autosomal recessive multiple congenital anomaly syndrome. Affected children present in the newborn period with profound hypotonia, seizures, and inability to feed. Characteristic craniofacial anomalies, eye abnormalities, neuronal migration defects, hepatomegaly, and chondrodysplasia punctata are present. Children with this condition do not show any significant development and usually die in the first year of life (summary by Steinberg et al., 2006). For a complete phenotypic description and a discussion of genetic heterogeneity of Zellweger syndrome, see 214100. Individuals with PBDs of complementation group 2 (CG2) have mutations in the PEX5 gene. For information on the history of PBD complementation groups, see 214100.

Primary shunt hyperbilirubinemia (PSHB) is a rare form of clinical jaundice characterized by increased serum levels of unconjugated bilirubin associated with ineffective erythropoiesis and a hyperplastic bone marrow. Peripheral red blood cell survival is normal (summary by Wang et al., 2006). Although primary shunt hyperbilirubinemia is clinically similar to Gilbert syndrome (143500), affected individuals do not have impaired activity of UDP-glucuronosyltransferase (UGT1A1; 191740). The term 'shunt' refers to a 'shortcut' in bilirubin production, from the bone marrow or from very young red blood cells as opposed to being derived from the hemoglobin of mature circulating erythrocytes (Israels et al., 1959).

The peroxisomal biogenesis disorder (PBD) Zellweger syndrome (ZS) is an autosomal recessive multiple congenital anomaly syndrome. Affected children present in the newborn period with profound hypotonia, seizures, and inability to feed. Characteristic craniofacial anomalies, eye abnormalities, neuronal migration defects, hepatomegaly, and chondrodysplasia punctata are present. Children with this condition do not show any significant development and usually die in the first year of life (summary by Steinberg et al., 2006). For a complete phenotypic description and a discussion of genetic heterogeneity of Zellweger syndrome, see 214100. Individuals with PBDs of complementation group 5 (CG5, equivalent to CG10 and CGF) have mutations in the PEX2 gene. For information on the history of PBD complementation groups, see 214100.

Zellweger syndrome (ZS) is an autosomal recessive multiple congenital anomaly syndrome resulting from disordered peroxisome biogenesis. Affected children present in the newborn period with profound hypotonia, seizures, and inability to feed. Characteristic craniofacial anomalies, eye abnormalities, neuronal migration defects, hepatomegaly, and chondrodysplasia punctata are present. Children with this condition do not show any significant development and usually die in the first year of life (summary by Steinberg et al., 2006). For a complete phenotypic description and a discussion of genetic heterogeneity of Zellweger syndrome, see 214100. Individuals with PBDs of complementation group 9 (CG9, equivalent to CGD) have mutations in the PEX16 gene. For information on the history of PBD complementation groups, see 214100.

Zellweger syndrome (ZS) is an autosomal recessive multiple congenital anomaly syndrome resulting from disordered peroxisome biogenesis. Affected children present in the newborn period with profound hypotonia, seizures, and inability to feed. Characteristic craniofacial anomalies, eye abnormalities, neuronal migration defects, hepatomegaly, and chondrodysplasia punctata are present. Children with this condition do not show any significant development and usually die in the first year of life (summary by Steinberg et al., 2006). For a complete phenotypic description and a discussion of genetic heterogeneity of Zellweger syndrome, see 214100. Individuals with PBDs of complementation group K (CGK) have mutations in the PEX14 gene. For information on the history of PBD complementation groups, see 214100.

Intrahepatic cholestasis of pregnancy is a reversible form of cholestasis that occurs most often in the third trimester of pregnancy and recurs in 45 to 70% of subsequent pregnancies. Symptoms include pruritus, jaundice, increased serum bile salts, and abnormal liver enzymes, all of which resolve rapidly after delivery. However, the condition is associated with fetal complications, including placental insufficiency, premature labor, fetal distress, and intrauterine death. Women with ICP are also susceptible to oral contraceptive-induced cholestasis (OCIC). Ursodeoxycholic acid (UDCA) is an effective treatment for conditions caused by ABCB4 mutations (summary by Pasmant et al., 2012). Mutation in the ABCB4 gene accounts for about 15% of ICP cases (summary by Ziol et al., 2008). For a discussion of genetic heterogeneity of ICP, see ICP1 (147480).

Infantile liver failure syndrome-2 (ILFS2) is an autosomal recessive disorder characterized by recurrent episodes of acute liver failure during intercurrent febrile illness. Patients first present in infancy or early childhood, and there is complete recovery between episodes with conservative treatment (summary by Haack et al., 2015). For a discussion of genetic heterogeneity of infantile liver failure syndrome, see ILFS1 (615438).

Congenital dyserythropoietic anemia type I (CDA I) is characterized by moderate-to-severe macrocytic anemia presenting occasionally in utero as severe anemia associated with hydrops fetalis but more commonly in neonates as hepatomegaly, early jaundice, and intrauterine growth restriction. Some individuals present in childhood or adulthood. After the neonatal period, most affected individuals have lifelong moderate anemia, usually accompanied by jaundice and splenomegaly. Secondary hemochromatosis develops with age as a result of increased iron absorption even in those who are not transfused. Distal limb anomalies occur in 4%-14% of affected individuals.

Most children with carbonic anhydrase VA (CA-VA) deficiency reported to date have presented between day 2 of life and early childhood (up to age 20 months) with hyperammonemic encephalopathy (i.e., lethargy, feeding intolerance, weight loss, tachypnea, seizures, and coma). Given that fewer than 20 affected individuals have been reported to date, the ranges of initial presentations and long-term prognoses are not completely understood. As of 2021 the oldest known affected individual is an adolescent. Almost all affected individuals reported to date have shown normal psychomotor development and no further episodes of metabolic crisis; however, a few have shown mild learning difficulties or delayed motor skills.

Zellweger syndrome (ZS) is an autosomal recessive multiple congenital anomaly syndrome resulting from disordered peroxisome biogenesis. Affected children present in the newborn period with profound hypotonia, seizures, and inability to feed. Characteristic craniofacial anomalies, eye abnormalities, neuronal migration defects, hepatomegaly, and chondrodysplasia punctata are present. Children with this condition do not show any significant development and usually die in the first year of life (summary by Steinberg et al., 2006). For a complete phenotypic description and a discussion of genetic heterogeneity of Zellweger syndrome, see 214100. Individuals with PBDs of complementation group 8 (CG8, equivalent to CGA) have mutations in the PEX26 gene. For information on the history of PBD complementation groups, see 214100.

Sideroblastic anemia-3 is an autosomal recessive hematologic disorder characterized by onset of anemia in adulthood. Affected individuals show signs of systemic iron overload, and iron chelation therapy may be of clinical benefit (summary by Liu et al., 2014). For a discussion of genetic heterogeneity of sideroblastic anemia, see SIDBA1 (300751).

In dehydrated hereditary stomatocytosis (DHS), also known as hereditary xerocytosis, red blood cells exhibit altered intracellular cation content and cellular dehydration, resulting in increased erythrocyte mean corpuscular hemoglobin concentration (MCHC) and decreased erythrocyte osmotic fragility. Blood films show various cell shape abnormalities, the most characteristic being the stomatocyte, with a straight or crescent-shaped central pallor (summary by Rapetti-Mauss et al., 2015). For discussion of clinical and genetic heterogeneity of the stomatocytoses, see DHS1 (194380).

Any congenital bile acid synthesis defect in which the cause of the disease is a mutation in the ABCD3 gene.

MGCA8 is an autosomal recessive metabolic disorder resulting in death in infancy. Features include hypotonia, abnormal movements, respiratory insufficiency with apneic episodes, and lack of developmental progress, often with seizures. Brain imaging is variable, but may show progressive cerebral atrophy. Laboratory studies show increased serum lactate and 3-methylglutaconic aciduria, suggesting a mitochondrial defect (summary by Mandel et al., 2016). For a phenotypic description and a discussion of genetic heterogeneity of 3-methylglutaconic aciduria, see MGCA type I (250950).

Any mitochondrial DNA depletion syndrome in which the cause of the disease is a mutation in the TFAM gene.

GRIDHH is an autosomal recessive multisystem disorder characterized by poor overall growth, impaired intellectual development, hypotonia, and variable liver dysfunction. Additional features, such as seizures and hearing loss, may also be present (summary by Kopajtich et al., 2016).

Progressive familial intrahepatic cholestasis-5 (PFIC5) is an autosomal recessive severe liver disorder characterized by onset of intralobular cholestasis in the neonatal period. The disease is rapidly progressive, leading to liver failure and death if liver transplant is not performed. Other features include abnormal liver enzymes, low to normal gamma-glutamyl transferase (GGT) activity, increased alpha-fetoprotein, and a vitamin K-independent coagulopathy (summary by Gomez-Ospina et al., 2016). For a general phenotypic description and a discussion of genetic heterogeneity of PFIC, see PFIC1 (211600).

Neonatal sclerosing cholangitis (NSC) is a rare autosomal recessive form of severe liver disease with onset in infancy. Affected infants have jaundice, cholestasis, acholic stools, and progressive liver dysfunction resulting in fibrosis and cirrhosis; most require liver transplantation in the first few decades of life. Cholangiography shows patent biliary ducts, but there are bile duct irregularities (summary by Girard et al., 2016; Grammatikopoulos et al., 2016).

Biliary atresia is a disorder of infants in which there is progressive obliteration or discontinuity of the extrahepatic biliary system, resulting in obstruction of bile flow. Untreated, the resulting cholestasis leads to progressive conjugated hyperbilirubinemia, cirrhosis, and hepatic failure (Bates et al., 1998). Most patients require liver transplantation within the first year of life (Leyva-Vega et al., 2010). See also Alagille syndrome (118450), which includes biliary atresia as a feature.

Familial Hemophagocytic lymphohistiocytosis (FHL) is a rare primary immunodeficiency characterized by a macrophage activation syndrome with an onset usually occurring within a few months or less common several years after birth.

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330). Genetic Heterogeneity of Asphyxiating Thoracic Dysplasia SRTD1 has been mapped to chromosome 15q13. See also SRTD2 (611263), caused by mutation in the IFT80 gene (611177); SRTD3 (613091), caused by mutation in the DYNC2H1 gene (603297); SRTD4 (613819), caused by mutation in the TTC21B gene (612014); SRTD5 (614376), caused by mutation in the WDR19 gene (608151); SRTD6 (263520), caused by mutation in the NEK1 gene (604588); SRTD7 (614091), caused by mutation in the WDR35 gene (613602); SRTD8 (615503), caused by mutation in the WDR60 gene (615462); SRTD9 (266920), caused by mutation in the IFT140 gene (614620); SRTD10 (615630), caused by mutation in the IFT172 gene (607386); SRTD11 (615633), caused by mutation in the WDR34 gene (613363); SRTD13 (616300), caused by mutation in the CEP120 gene (613446); SRTD14 (616546), caused by mutation in the KIAA0586 gene (610178); SRTD15 (617088), caused by mutation in the DYNC2LI1 gene (617083); SRTD16 (617102), caused by mutation in the IFT52 gene (617094); SRTD17 (617405), caused by mutation in the TCTEX1D2 gene (617353); SRTD18 (617866), caused by mutation in the IFT43 gene (614068); SRTD19 (617895), caused by mutation in the IFT81 gene (605489); SRTD20 (617925), caused by mutation in the INTU gene (610621); and SRTD21 (619479), caused by mutation in the KIAA0753 gene (617112). See also SRTD12 (Beemer-Langer syndrome; 269860).

The phenotypic spectrum of ATP8B1 deficiency ranges from severe through moderate to mild. Severe ATP8B1 deficiency is characterized by infantile-onset cholestasis that progresses to cirrhosis, hepatic failure, and early death. Although mild-to-moderate ATP8B1 deficiency initially was thought to involve intermittent symptomatic cholestasis with a lack of hepatic fibrosis, it is now known that hepatic fibrosis may be present early in the disease course. Furthermore, in some persons with ATP8B1 deficiency the clinical findings can span the phenotypic spectrum, shifting over time from the mild end of the spectrum (episodic cholestasis) to the severe end of the spectrum (persistent cholestasis). Sensorineural hearing loss (SNHL) is common across the phenotypic spectrum.

Trichohepatoenteric syndrome (THES), generally considered to be a neonatal enteropathy, is characterized by intractable diarrhea (seen in almost all affected children), woolly hair (seen in all), intrauterine growth restriction, facial dysmorphism, and short stature. Additional findings include poorly characterized immunodeficiency, recurrent infections, skin abnormalities, and liver disease. Mild intellectual disability (ID) is seen in about 50% of affected individuals. Less common findings include congenital heart defects and platelet anomalies. To date 52 affected individuals have been reported.

The two forms of deoxyguanosine kinase (DGUOK) deficiency are a neonatal multisystem disorder and an isolated hepatic disorder that presents later in infancy or childhood. The majority of affected individuals have the multisystem illness with hepatic disease (jaundice, cholestasis, hepatomegaly, and elevated transaminases) and neurologic manifestations (hypotonia, nystagmus, and psychomotor retardation) evident within weeks of birth. Those with isolated liver disease may also have renal involvement and some later develop mild hypotonia. Progressive hepatic disease is the most common cause of death in both forms.

Infantile liver failure syndrome-3 is an autosomal recessive disorder characterized by recurrent episodes of acute liver failure during intercurrent febrile illness. Patients first present in infancy or early childhood, and there usually is complete recovery between episodes with conservative treatment. Affected individuals also have skeletal anomalies of the vertebral bodies and femoral heads (summary by Cousin et al., 2019). For a discussion of genetic heterogeneity of infantile liver failure syndrome, see ILFS1 (615438).

Congenital disorder of glycosylation type 2R (CDG2R) is an X-linked recessive disorder characterized by infantile onset of liver failure, recurrent infections due to hypogammaglobulinemia, and cutis laxa. Some patients may also have mild intellectual impairment and dysmorphic features. Laboratory studies showed defective glycosylation of serum transferrin in a type 2 pattern (summary by Rujano et al., 2017). For an overview of congenital disorders of glycosylation, see CDG1A (212065) and CDG2A (212066).

Bile acid conjugation defect-1 (BACD1) is an autosomal recessive metabolic disorder characterized by onset of symptoms, including jaundice and failure to thrive, in early infancy. The clinical features of the disorder result from impaired absorption of fat-soluble vitamins. Vitamin D deficiency causes rickets with variable growth deficiency, and vitamin K deficiency causes a coagulopathy with decreased production of vitamin K-dependent clotting factors. More variable features may include pruritis, anemia, hepatomegaly, and bile duct proliferation on liver biopsy. Laboratory studies show abnormally increased levels of unconjugated bile acids (summary by Setchell et al., 2013). See also familial hypercholanemia (FHCA; 607748), in which patients have increased serum bile levels of conjugated bile acids.

Developmental delay, impaired speech, and behavioral abnormalities (DDISBA) is characterized by global developmental delay apparent from early childhood. Intellectual disability can range from mild to severe. Additional variable features may include dysmorphic facial features, seizures, hypotonia, motor abnormalities such as Tourette syndrome or dystonia, and hearing loss (summary by Cousin et al., 2021).

Biliary, renal, neurologic, and skeletal syndrome (BRENS) is an autosomal recessive complex ciliopathy with multisystemic manifestations. The most common presentation is severe neonatal cholestasis that progresses to liver fibrosis and cirrhosis. Most patients have additional clinical features suggestive of a ciliopathy, including postaxial polydactyly, hydrocephalus, retinal abnormalities, and situs inversus. Additional features of the syndrome may include congenital cardiac defects, echogenic kidneys with renal failure, ocular abnormalities, joint hyperextensibility, and dysmorphic facial features. Some patients have global developmental delay. Brain imaging typically shows dilated ventricles, hypomyelination, and white matter abnormalities, although some patients have been described with abnormal pituitary development (summary by Shaheen et al., 2020 and David et al., 2020).

Progressive intrahepatic cholestasis-7 with or without hearing loss (PFIC7) is an autosomal recessive liver disorder characterized by infantile-onset jaundice and itching associated with cholestasis, elevated alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and normal gamma glutamyltransferase (GGT). Liver biopsy shows hepatocellular and canalicular cholestasis with fibrotic changes. Many patients have resolution of the liver abnormalities with age, although some may have persistent liver enzyme abnormalities or splenomegaly. A subset of patients develops hearing loss in childhood between early infancy and the teenage years. Rifampicin may be effective for pruritis (summary by Maddirevula et al., 2019). For a discussion of genetic heterogeneity of PFIC, see PFIC1 (211600).

Progressive familial intrahepatic cholestasis-8 (PFIC8) is an autosomal recessive disorder characterized by cholestasis and high gamma-glutamyltransferase presenting in the infantile period (summary by Unlusoy Aksu et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of PFIC, see PFIC1 (211600).

Immunodeficiency-87 and autoimmunity (IMD87) is an autosomal recessive immunologic disorder with wide phenotypic variation and severity. Affected individuals usually present in infancy or early childhood with increased susceptibility to infections, often Epstein-Barr virus (EBV), as well as with lymphadenopathy or autoimmune manifestations, predominantly hemolytic anemia. Laboratory studies may show low or normal lymphocyte numbers, often with skewed T-cell subset ratios. The disorder results primarily from defects in T-cell function, which causes both immunodeficiency and overall immune dysregulation (summary by Serwas et al., 2019 and Fournier et al., 2021).

Congenital dyserythropoietic anemia type IIIa (CDAN3A) is a rare autosomal dominant hematologic disorder characterized by nonprogressive mild to moderate hemolytic anemia, macrocytosis in the peripheral blood, intravascular hemolysis, and giant multinucleated erythroblasts in the bone marrow. The disorder results from ineffective erythropoiesis. Laboratory studies show evidence of intravascular hemolysis, including increased thymidine kinase, lactate dehydrogenase, and/or undetectable haptoglobin (summary by Lind et al., 1995; Liljeholm et al., 2013). For a discussion of genetic heterogeneity of congenital dyserythropoietic anemia, see 224120.

Progressive familial intrahepatic cholestasis-9 (PFIC9) is an autosomal recessive disorder characterized by onset of cholestasis associated with increased serum gamma-glutamyltransferase (GGT) in infancy or early childhood. Affected individuals have hepatosplenomegaly and may have portal hypertension or upper gastrointestinal bleeding. Liver biopsy shows fibrosis, cirrhosis, bile duct proliferation, and abnormal bile duct morphology. The disorder is thought to result from ciliary defects in cholangiocytes, consistent with a ciliopathy that appears to be restricted to the liver. Treatment with ursodeoxycholic acid (UDCA) or liver transplant is effective (Luan et al., 2021). For a discussion of genetic heterogeneity of progressive familial intrahepatic cholestasis, see PFIC1 (211600).

Progressive familial intrahepatic cholestasis-10 (PFIC10) is an autosomal recessive liver disorder characterized by the onset of symptoms in the first months or years of life. Features include jaundice, pruritis, and hepatomegaly associated with increased serum bilirubin and bile acids. Liver transaminases may be variably increased, but gamma-glutamyltransferase (GGT; see 612346) is normal. Liver biopsy shows hepatocellular and canalicular cholestasis with giant cell changes. Although rare patients may have episodes of diarrhea and even show endoscopic features of microvillus inclusion disease (MVID), this tends to be transient and cholestasis dominates the clinical picture (Gonzales et al., 2017; Cockar et al., 2020). For a discussion of genetic heterogeneity of progressive familial intrahepatic cholestasis, see PFIC1 (211600).

Hepatorenocardiac degenerative fibrosis (HRCDF) is a primarily fibrotic disease affecting the liver, kidney, and heart, with considerable variability in disease onset and expression. Affected individuals develop degenerative hepatic fibrosis in childhood or early adulthood, with variable later onset of fibrocystic kidney disease and hypertrophic cardiomyopathy (Devane et al., 2022).

Severe congenital liver disease (SCOLIV) is an autosomal recessive disorder characterized by the onset of progressive hepatic dysfunction usually in the first years of life. Affected individuals show feeding difficulties with failure to thrive and features such as jaundice, hepatomegaly, and abdominal distension. Laboratory workup is consistent with hepatic insufficiency and may also show coagulation defects, anemia, or metabolic disturbances. Cirrhosis and hypernodularity are commonly observed on liver biopsy. Many patients die of liver failure in early childhood (Moreno Traspas et al., 2022).

Progressive familial intrahepatic cholestasis-12 (PFIC12) is characterized by neonatal-onset jaundice and conjugated hyperbilirubinemia, associated with intense pruritus. Transaminases are mildly elevated but GGT (see 612346) is normal. Hepatosplenomegaly and mildly prolonged activated partial thromboplastin time (APTT) have been observed in some patients (Qiu et al., 2019).

Systemic autoinflammatory disease with vasculitis (SAIDV) is an autosomal dominant disorder that manifests soon after birth with features such as purpuric skin rash, fever, hepatosplenomegaly, and elevated C-reactive protein (CRP; 123260). Laboratory studies may show leukocytosis, thrombocytopenia, and autoantibodies. A subset of patients develop progressive liver involvement that may result in fibrosis. Other systemic features, such as periorbital edema, conjunctivitis, infections, abdominal pain, and arthralgia are usually observed. Mutations occur de novo. De Jesus et al. (2023) referred to this disorder as LAVLI (LYN kinase-associated vasculopathy and liver fibrosis).