Cleidocranial dysplasia (CCD) spectrum disorder is a skeletal dysplasia that represents a clinical continuum ranging from classic CCD (triad of delayed closure of the cranial sutures, hypoplastic or aplastic clavicles, and dental abnormalities) to mild CCD to isolated dental anomalies without the skeletal features. Most individuals come to diagnosis because they have classic features. At birth, affected individuals typically have abnormally large, wide-open fontanelles that may remain open throughout life. Clavicular hypoplasia can result in narrow, sloping shoulders that can be opposed at the midline. Moderate short stature may be observed, with most affected individuals being shorter than their unaffected sibs. Dental anomalies may include supernumerary teeth, eruption failure of the permanent teeth, and presence of the second permanent molar with the primary dentition. Individuals with CCD spectrum disorder are at increased risk of developing recurrent sinus infections, recurrent ear infections leading to conductive hearing loss, and upper-airway obstruction. Intelligence is typically normal.

Pierre Robin sequence is a craniofacial anomaly comprising mandibular hypoplasia, cleft secondary palate, and glossoptosis leading to life-threatening obstructive apnea and feeding difficulties during the neonatal period (summary by Tan et al., 2013).

Multiple pterygium syndromes comprise a group of multiple congenital anomaly disorders characterized by webbing (pterygia) of the neck, elbows, and/or knees and joint contractures (arthrogryposis) (Morgan et al., 2006). The multiple pterygium syndromes are phenotypically and genetically heterogeneous but are traditionally divided into prenatally lethal (253290) and nonlethal (Escobar) types.

Cerebrocostomandibular syndrome (CCMS) is a rare autosomal dominant disorder characterized by branchial arch-derivative and thoracic malformations. A key craniofacial characteristic is micrognathia, often associated with cleft palate and feeding and airway difficulties. Patients with CCMS have a narrow chest and striking posterior rib gaps which distinguish this condition (summary by Tooley et al., 2016). See CDG2G (611209) for a cerebrocostomandibular-like syndrome.

D-glyceric aciduria is a rare autosomal recessive metabolic disorder with a highly variable phenotype. Some patients have an encephalopathic presentation, with severe mental retardation, seizures, microcephaly, and sometimes early death, whereas others have a mild phenotype with only mild speech delay or even normal development (summary by Sass et al., 2010).

Malonyl-CoA decarboxylase deficiency is an uncommon inherited metabolic disease. The characteristic phenotype is variable, but may include developmental delay in early childhood, seizures, hypotonia, diarrhea, vomiting, metabolic acidosis, hypoglycemia, ketosis, abnormal urinary compounds, lactic acidemia, and hypertrophic cardiomyopathy (Sweetman and Williams, 2001).

The nephrotic syndrome is characterized clinically by proteinuria, hypoalbuminemia, hyperlipidemia, and edema. Kidney biopsies show nonspecific histologic changes such as minimal change, focal segmental glomerulosclerosis (FSGS), and diffuse mesangial proliferation. Approximately 20% of affected individuals have an inherited steroid-resistant form and progress to end-stage renal failure (summary by Fuchshuber et al., 1996). Nephrotic syndrome type 1 (NPHS1) is characterized by prenatal onset of massive proteinuria followed by severe steroid-resistant nephrotic syndrome apparent at birth with rapid progression to end-stage renal failure (Kestila et al., 1998). Because of confusion in the literature regarding use of the terms 'nephrotic syndrome' and 'focal segmental glomerulosclerosis' (see NOMENCLATURE section), these disorders in OMIM are classified as NPHS or FSGS according to how they were first designated in the literature. Genetic Heterogeneity of Nephrotic Syndrome and Focal Segmental Glomerulosclerosis Nephrotic syndrome and FSGS are genetically heterogeneous disorders representing a spectrum of hereditary renal diseases. See also NPHS2 (600995), caused by mutation in the podocin gene (604766); NPHS3 (610725), caused by mutation in the PLCE1 gene (608414); NPHS4 (256370), caused by mutation in the WT1 gene (607102); NPHS5 (614199), caused by mutation in the LAMB2 gene (150325); NPHS6 (614196), caused by mutation in the PTPRO gene (600579); NPHS7 (615008), caused by mutation in the DGKE gene (601440); NPHS8 (615244), caused by mutation in the ARHGDIA gene (601925); NPHS9 (615573), caused by mutation in the COQ8B gene (615567); NPHS10 (615861), caused by mutation in the EMP2 gene (602334); NPHS11 (616730), caused by mutation in the NUP107 gene (607617); NPHS12 (616892), caused by mutation in the NUP93 gene (614351); NPHS13 (616893), caused by mutation in the NUP205 gene (614352); NPHS14 (617575), caused by mutation in the SGPL1 gene (603729); NPHS15 (617609), caused by mutation in the MAGI2 gene (606382); NPHS16 (617783), caused by mutation in the KANK2 gene (614610), NPHS17 (618176), caused by mutation in the NUP85 gene (170285); NPHS18 (618177), caused by mutation in the NUP133 gene (607613); NPHS19 (618178), caused by mutation in the NUP160 gene (607614); NPHS20 (301028), caused by mutation in the TBC1D8B gene (301027); NPHS21 (618594) caused by mutation in the AVIL gene (613397); NPHS22 (619155), caused by mutation in the NOS1AP gene (605551); NPHS23 (619201), caused by mutation in the KIRREL1 gene (607428); NPHS24 (619263), caused by mutation in the DAAM2 gene (606627); and NPHS26 (620049), caused by mutation in the LAMA5 gene (601033). The symbol NPHS25 has been used as an alternative designation for NPHS21. See also FSGS1 (603278), caused by mutation in the ACTN4 gene (604638); FSGS2 (603965), caused by mutation in the TRPC6 gene (603652); FSGS3 (607832), associated with variation in the CD2AP gene (604241); FSGS4 (612551), mapped to chromosome 22q12; FSGS5 (613237), caused by mutation in the INF2 gene (610982); FSGS6 (614131), caused by mutation in the MYO1E gene (601479); FSGS7 (616002), caused by mutation in the PAX2 gene (167409); FSGS8 (616032), caused by mutation in the ANLN gene (616027); and FSGS9 (616220), caused by mutation in the CRB2 gene (609720).

X-linked myotubular myopathy (X-MTM), also known as myotubular myopathy (MTM), is characterized by muscle weakness that ranges from severe to mild. Approximately 80% of affected males present with severe (classic) X-MTM characterized by polyhydramnios, decreased fetal movement, and neonatal weakness, hypotonia, and respiratory failure. Motor milestones are significantly delayed and most individuals fail to achieve independent ambulation. Weakness is profound and often involves facial and extraocular muscles. Respiratory failure is nearly uniform, with most individuals requiring 24-hour ventilatory assistance. It is estimated that at least 25% of boys with severe X-MTM die in the first year of life, and those who survive rarely live into adulthood. Males with mild or moderate X-MTM (~20%) achieve motor milestones more quickly than males with the severe form; many ambulate independently, and may live into adulthood. Most require gastrostomy tubes and/or ventilator support. In all subtypes of X-MTM, the muscle disease is not obviously progressive. Female carriers of X-MTM are generally asymptomatic, although manifesting heterozygotes are increasingly being identified. In affected females, symptoms range from severe, generalized weakness presenting in childhood, with infantile onset similar to affected male patients, to mild (often asymmetric) weakness manifesting in adulthood. Affected adult females may experience progressive respiratory decline and ultimately require ventilatory support.

Simpson-Golabi-Behmel syndrome type 1 (SGBS1) is characterized by pre- and postnatal macrosomia; distinctive craniofacial features (including macrocephaly, coarse facial features, macrostomia, macroglossia, and palatal abnormalities); and commonly, mild-to-severe intellectual disability with or without structural brain anomalies. Other variable findings include supernumerary nipples, diastasis recti / umbilical hernia, congenital heart defects, diaphragmatic hernia, genitourinary defects, and gastrointestinal anomalies. Skeletal anomalies can include vertebral fusion, scoliosis, rib anomalies, and congenital hip dislocation. Hand anomalies can include large hands and postaxial polydactyly. Affected individuals are at increased risk for embryonal tumors including Wilms tumor, hepatoblastoma, adrenal neuroblastoma, gonadoblastoma, hepatocellular carcinoma, and medulloblastoma.

Toriello-Carey syndrome is a multiple congenital anomaly disorder with variable systemic manifestations, most commonly including mental retardation, agenesis of the corpus callosum, postnatal growth delay, cardiac defects, usually septal defects, distal limb defects, and urogenital anomalies in affected males. Patients have facial dysmorphic features, micrognathia, including full cheeks, hypertelorism, flattened nasal bridge, anteverted nares, and short neck. Not all features are found in all patients and some patients may have additional features such as anal anomalies or hernias (summary by Toriello et al., 2003). In a review of the Toriello-Carey syndrome, Toriello et al. (2016) stated that while corpus callosum abnormalities and micrognathia with highly arched or cleft palate are seen in most patients, other manifestations are widely variable. They noted that etiologic heterogeneity has been observed in reported patients, with at least 20% of patients having chromosome anomalies, and that no good candidate genes have been identified by exome sequencing. The authors commented that this condition might not be a unitary diagnostic entity. They recommended chromosome microarray for any child suspected of having the condition, followed by standard of care by genetic testing.

Wieacker-Wolff syndrome (WRWF) is a severe X-linked recessive neurodevelopmental disorder affecting the central and peripheral nervous systems. It is characterized by onset of muscle weakness in utero (fetal akinesia), which results in arthrogryposis multiplex congenita (AMC) apparent at birth. Affected boys are born with severe contractures, show delayed motor development, facial and bulbar weakness, characteristic dysmorphic facial features, and skeletal abnormalities, such as hip dislocation, scoliosis, and foot deformities. Additional features include global developmental delay with poor or absent speech and impaired intellectual development, feeding difficulties and poor growth, hypotonia, hypogenitalism, and spasticity. Carrier females may be unaffected or have mild features of the disorder (summary by Hirata et al., 2013 and Frints et al., 2019).

Bohring-Opitz syndrome (BOS) is characterized by distinctive facial features and posture, growth failure, variable but usually severe intellectual disability, and variable anomalies. The facial features may include microcephaly or trigonocephaly / prominent (but not fused) metopic ridge, hypotonic facies with full cheeks, synophrys, glabellar and eyelid nevus flammeus (simplex), prominent globes, widely set eyes, palate anomalies, and micrognathia. The BOS posture, which is most striking in early childhood and often becomes less apparent with age, is characterized by flexion at the elbows with ulnar deviation and flexion of the wrists and metacarpophalangeal joints. Feeding difficulties in early childhood, including cyclic vomiting, have a significant impact on overall health; feeding tends to improve with age. Seizures are common and typically responsive to standard epileptic medications. Minor cardiac anomalies and transient bradycardia and apnea may be present. Affected individuals may experience recurrent infections, which also tend to improve with age. Isolated case reports suggest that individuals with BOS are at greater risk for Wilms tumor than the general population, but large-scale epidemiologic studies have not been conducted.

WT1 disorder is characterized by congenital/infantile or childhood onset of steroid-resistant nephrotic syndrome (SRNS), a progressive glomerulopathy that does not respond to standard steroid therapy. Additional common findings can include disorders of testicular development (with or without abnormalities of the external genitalia and/or müllerian structures) and Wilms tumor. Less common findings are congenital anomalies of the kidney and urinary tract (CAKUT) and gonadoblastoma. While various combinations of renal and other findings associated with a WT1 pathogenic variant were designated as certain syndromes in the past, those designations are now recognized to be part of a phenotypic continuum and are no longer clinically helpful.

Carnitine palmitoyltransferase II (CPT II) deficiency is a disorder of long-chain fatty-acid oxidation. The three clinical presentations are lethal neonatal form, severe infantile hepatocardiomuscular form, and myopathic form (which is usually mild and can manifest from infancy to adulthood). While the former two are severe multisystemic diseases characterized by liver failure with hypoketotic hypoglycemia, cardiomyopathy, seizures, and early death, the latter is characterized by exercise-induced muscle pain and weakness, sometimes associated with myoglobinuria. The myopathic form of CPT II deficiency is the most common disorder of lipid metabolism affecting skeletal muscle and the most frequent cause of hereditary myoglobinuria. Males are more likely to be affected than females.

Primary ciliary dyskinesia-5 (CILD5) is an autosomal recessive disorder characterized by early onset of a progressive decline in lung function due to an inability to clear mucus and particles from the airways. Affected individuals have recurrent infections of the sinuses, ears, airways, and lungs. Sperm motility is also decreased. Individuals with CILD5 do not have situs inversus (summary by Olbrich et al., 2012). For a general phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

Primary ciliary dyskinesia (PCD; CILD) is an autosomal recessive disorder resulting from loss of normal ciliary function. Kartagener (pronounced KART-agayner) syndrome is characterized by the combination of primary ciliary dyskinesia and situs inversus, and occurs in approximately half of patients with ciliary dyskinesia. Since normal nodal ciliary movement in the embryo is required for normal visceral asymmetry, absence of normal ciliary movement results in a lack of definitive patterning; thus, random chance alone appears to determine whether the viscera take up the normal or reversed left-right position during embryogenesis. This explains why approximately 50% of patients, even within the same family, have situs inversus (summary by Afzelius, 1976; El Zein et al., 2003). For a general phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia and the Kartagener syndrome, see CILD1 (244400).

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.

Simpson-Golabi-Behmel syndrome type 2 (SGBS2) is an X-linked recessive disorder in which affected males have severely impaired intellectual development, ciliary dyskinesia, and macrocephaly (summary by Budny et al., 2006). For a general phenotypic description and a discussion of genetic heterogeneity of Simpson-Golabi-Behmel syndrome, see 312870.

Pyridoxine-dependent epilepsy – ALDH7A1 (PDE-ALDH7A1) is characterized by seizures not well controlled with anti-seizure medication that are responsive clinically and electrographically to large daily supplements of pyridoxine (vitamin B6). This is true across a phenotypic spectrum that ranges from classic to atypical PDE-ALDH7A1. Intellectual disability is common, particularly in classic PDE-ALDH7A1. Classic PDE-ALDH7A1. Untreated seizures begin within the first weeks to months of life. Dramatic presentations of prolonged seizures and recurrent episodes of status epilepticus are typical; recurrent self-limited events including partial seizures, generalized seizures, atonic seizures, myoclonic events, and infantile spasms also occur. Electrographic seizures can occur without clinical correlates. Atypical PDE-ALDH7A1. Findings in untreated individuals can include late-onset seizures beginning between late infancy and age three years, seizures that initially respond to anti-seizure medication and then become intractable, seizures during early life that do not respond to pyridoxine but are subsequently controlled with pyridoxine several months later, and prolonged seizure-free intervals (=5 months) that occur after discontinuation of pyridoxine.

The category of 3-methylglutaconic aciduria type IV (MGCA4) represents a heterogeneous unclassified group of patients who share mild or intermittent urinary excretion of 3-methylglutaconic acid. MGCA excretion is a nonspecific finding observed in many other disorders caused by defects in mitochondrial energy metabolism (Gunay-Aygun, 2005). For a general phenotypic description and a discussion of genetic heterogeneity of 3-methylglutaconic aciduria, see MGCA1 (250950)

Kaufman oculocerebrofacial syndrome (KOS) is characterized by developmental delay, severe intellectual disability, and distinctive craniofacial features. Most affected children have prenatal-onset microcephaly, hypotonia, and growth deficiency. Feeding issues, ocular abnormalities, hearing impairment, and respiratory tract abnormalities are common. Ocular abnormalities can include structural abnormalities (microcornea or microphthalmia, coloboma, optic nerve hypoplasia), refractive errors (myopia ± astigmatism, hyperopia), strabismus, and entropion. Both conductive and sensorineural hearing loss have been reported as well as mixed conductive-sensorineural hearing loss of variable severity. Breathing problems can lead to prolonged hospitalization after birth in more than half of individuals. Less common findings include ectodermal abnormalities, cardiac manifestations, urogenital abnormalities, seizures, and skeletal abnormalities.

Campomelic dysplasia (CD) is a skeletal dysplasia characterized by distinctive facies, Pierre Robin sequence with cleft palate, shortening and bowing of long bones, and clubfeet. Other findings include laryngotracheomalacia with respiratory compromise and ambiguous genitalia or normal female external genitalia in most individuals with a 46,XY karyotype. Many affected infants die in the neonatal period; additional findings identified in long-term survivors include short stature, cervical spine instability with cord compression, progressive scoliosis, and hearing impairment.

Congenital glutamine deficiency (GLND) is a severe autosomal recessive disorder characterized by onset at birth of encephalopathy, lack of normal development, seizures, and hypotonia associated with variable brain abnormalities (summary by Haberle et al., 2011).

Short stature, auditory canal atresia, mandibular hypoplasia, and skeletal abnormalities (SAMS) is an autosomal recessive multiple congenital anomaly syndrome with features of a first and second branchial arch syndrome. Craniofacial abnormalities can lead to conductive hearing loss, respiratory insufficiency, and feeding difficulties. Additional features include rhizomelic skeletal anomalies as well as abnormalities of the shoulder and pelvic joints. Affected individuals may also have some features of a neurocristopathy or abnormal mesoderm development, such as urogenital anomalies, that are distinct from other branchial arch syndromes (summary by Parry et al., 2013).

A very rare inherited malformation syndrome with characteristics of omphalocele, scoliosis, mild dysmorphic features (downslanted palpebral fissures, s-shaped eyelids and thin upper lip), laryngeal and pharyngeal hypoplasia and learning disabilities.

Thanatophoric dysplasia (TD) is a short-limb skeletal dysplasia that is usually lethal in the perinatal period. TD is divided into subtypes: TD type I is characterized by micromelia with bowed femurs and, uncommonly, the presence of craniosynostosis of varying severity. TD type II is characterized by micromelia with straight femurs and uniform presence of moderate-to-severe craniosynostosis with cloverleaf skull deformity. Other features common to type I and type II include: short ribs, narrow thorax, relative macrocephaly, distinctive facial features, brachydactyly, hypotonia, and redundant skin folds along the limbs. Most affected infants die of respiratory insufficiency shortly after birth. Rare long-term survivors have been reported.

The main cause of respiratory distress syndrome (RDS) in premature infants is a developmental deficiency of pulmonary surfactant. The frequency of RDS is inversely proportional to gestational age. However, not all infants born prematurely develop RDS, suggesting that there may be susceptibility factors. Because multiple factors can contribute to the pathogenesis of RDS specifically in premature infants, the etiology is considered to be multifactorial (summaries by Ramet et al., 2000; Clark and Clark, 2005). Pathogenic germline mutations in several genes involved in surfactant metabolism, including SFTPB (178640) and SFTPC (178620), can cause clinical features of respiratory distress syndrome in term neonates, children, and adults, disorders referred to as 'surfactant metabolism dysfunction' (see, e.g., SMDP1, 265120). Susceptibility to the development of RDS in premature infants may be associated with polymorphisms in surfactant genes, such as surfactant protein A1 (SFTPA1; 178630), SFTPB, and SFTPC (see MOLECULAR GENETICS).

Inborn errors of pulmonary surfactant metabolism are genetically heterogeneous disorders resulting in severe respiratory insufficiency or failure in full-term neonates or infants. These disorders are associated with various pathologic entities, including pulmonary alveolar proteinosis (PAP), desquamative interstitial pneumonitis (DIP), or cellular nonspecific interstitial pneumonitis (NSIP) (Clark and Clark, 2005). A clinically similar disorder characterized by respiratory distress (267450) can affect preterm infants, who show developmental deficiency of surfactant. Acquired PAP (610910) is an autoimmune disorder characterized by the presence of autoantibodies to CSF2 (138960). Genetic Heterogeneity of Pulmonary Surfactant Metabolism Dysfunction See also SMDP2 (610913), caused by mutation in the SPTPC gene (178620) on 8p21; SMDP3 (610921), caused by mutation in the ABCA3 gene (601615) on 16p13; SMDP4 (300770), caused by mutation in the CSF2RA gene (306250) on Xp22; and SMDP5 (614370), caused by mutation in the CSF2RB gene (138981) on 22q12.

NKX2-1-related disorders range from benign hereditary chorea (BHC) to choreoathetosis, congenital hypothyroidism, and neonatal respiratory distress (also known as brain-lung-thyroid syndrome). Childhood-onset chorea, the hallmark of NKX2-1-related disorders, may or may not be associated with respiratory distress syndrome or congenital hypothyroidism. Chorea generally begins in early infancy or about age one year (most commonly) or in late childhood or adolescence, and progresses into the second decade after which it remains static or (rarely) remits. Pulmonary disease, the second most common manifestation, can include respiratory distress syndrome in neonates, interstitial lung disease in young children, and pulmonary fibrosis in older persons. The risk for pulmonary carcinoma is increased in young adults with an NKX2-1-related disorder. Thyroid dysfunction, the result of dysembryogenesis, can present as congenital hypothyroidism or compensated hypothyroidism. The risk for thyroid cancer is unknown and may not be increased. In one review, 50% of affected individuals had the full brain-lung-thyroid syndrome, 30% had involvement of brain and thyroid only, and 13% had isolated chorea only.

For a general phenotypic description and a discussion of genetic heterogeneity of pulmonary surfactant metabolism dysfunction, see SMDP1 (265120).

Primary ciliary dyskinesia is a disorder characterized by chronic respiratory tract infections, abnormally positioned internal organs, and the inability to have children (infertility). The signs and symptoms of this condition are caused by abnormal cilia and flagella. Cilia are microscopic, finger-like projections that stick out from the surface of cells. They are found in the linings of the airway, the reproductive system, and other organs and tissues. Flagella are tail-like structures, similar to cilia, that propel sperm cells forward.\n\nIn the respiratory tract, cilia move back and forth in a coordinated way to move mucus towards the throat. This movement of mucus helps to eliminate fluid, bacteria, and particles from the lungs. Most babies with primary ciliary dyskinesia experience breathing problems at birth, which suggests that cilia play an important role in clearing fetal fluid from the lungs. Beginning in early childhood, affected individuals develop frequent respiratory tract infections. Without properly functioning cilia in the airway, bacteria remain in the respiratory tract and cause infection. People with primary ciliary dyskinesia also have year-round nasal congestion and a chronic cough. Chronic respiratory tract infections can result in a condition called bronchiectasis, which damages the passages, called bronchi, leading from the windpipe to the lungs and can cause life-threatening breathing problems.\n\nSome individuals with primary ciliary dyskinesia have abnormally placed organs within their chest and abdomen. These abnormalities arise early in embryonic development when the differences between the left and right sides of the body are established. About 50 percent of people with primary ciliary dyskinesia have a mirror-image reversal of their internal organs (situs inversus totalis). For example, in these individuals the heart is on the right side of the body instead of on the left. Situs inversus totalis does not cause any apparent health problems. When someone with primary ciliary dyskinesia has situs inversus totalis, they are often said to have Kartagener syndrome.\n\nApproximately 12 percent of people with primary ciliary dyskinesia have a condition known as heterotaxy syndrome or situs ambiguus, which is characterized by abnormalities of the heart, liver, intestines, or spleen. These organs may be structurally abnormal or improperly positioned. In addition, affected individuals may lack a spleen (asplenia) or have multiple spleens (polysplenia). Heterotaxy syndrome results from problems establishing the left and right sides of the body during embryonic development. The severity of heterotaxy varies widely among affected individuals.\n\nPrimary ciliary dyskinesia can also lead to infertility. Vigorous movements of the flagella are necessary to propel the sperm cells forward to the female egg cell. Because their sperm do not move properly, males with primary ciliary dyskinesia are usually unable to father children. Infertility occurs in some affected females and is likely due to abnormal cilia in the fallopian tubes.\n\nAnother feature of primary ciliary dyskinesia is recurrent ear infections (otitis media), especially in young children. Otitis media can lead to permanent hearing loss if untreated. The ear infections are likely related to abnormal cilia within the inner ear.\n\nRarely, individuals with primary ciliary dyskinesia have an accumulation of fluid in the brain (hydrocephalus), likely due to abnormal cilia in the brain.

Rarely, individuals with primary ciliary dyskinesia have an accumulation of fluid in the brain (hydrocephalus), likely due to abnormal cilia in the brain.\n\nAnother feature of primary ciliary dyskinesia is recurrent ear infections (otitis media), especially in young children. Otitis media can lead to permanent hearing loss if untreated. The ear infections are likely related to abnormal cilia within the inner ear.\n\nPrimary ciliary dyskinesia can also lead to infertility. Vigorous movements of the flagella are necessary to propel the sperm cells forward to the female egg cell. Because their sperm do not move properly, males with primary ciliary dyskinesia are usually unable to father children. Infertility occurs in some affected females and is likely due to abnormal cilia in the fallopian tubes.\n\nApproximately 12 percent of people with primary ciliary dyskinesia have a condition known as heterotaxy syndrome or situs ambiguus, which is characterized by abnormalities of the heart, liver, intestines, or spleen. These organs may be structurally abnormal or improperly positioned. In addition, affected individuals may lack a spleen (asplenia) or have multiple spleens (polysplenia). Heterotaxy syndrome results from problems establishing the left and right sides of the body during embryonic development. The severity of heterotaxy varies widely among affected individuals.\n\nSome individuals with primary ciliary dyskinesia have abnormally placed organs within their chest and abdomen. These abnormalities arise early in embryonic development when the differences between the left and right sides of the body are established. About 50 percent of people with primary ciliary dyskinesia have a mirror-image reversal of their internal organs (situs inversus totalis). For example, in these individuals the heart is on the right side of the body instead of on the left. Situs inversus totalis does not cause any apparent health problems. When someone with primary ciliary dyskinesia has situs inversus totalis, they are often said to have Kartagener syndrome.\n\nIn the respiratory tract, cilia move back and forth in a coordinated way to move mucus towards the throat. This movement of mucus helps to eliminate fluid, bacteria, and particles from the lungs. Most babies with primary ciliary dyskinesia experience breathing problems at birth, which suggests that cilia play an important role in clearing fetal fluid from the lungs. Beginning in early childhood, affected individuals develop frequent respiratory tract infections. Without properly functioning cilia in the airway, bacteria remain in the respiratory tract and cause infection. People with primary ciliary dyskinesia also have year-round nasal congestion and a chronic cough. Chronic respiratory tract infections can result in a condition called bronchiectasis, which damages the passages, called bronchi, leading from the windpipe to the lungs and can cause life-threatening breathing problems.\n\nPrimary ciliary dyskinesia is a disorder characterized by chronic respiratory tract infections, abnormally positioned internal organs, and the inability to have children (infertility). The signs and symptoms of this condition are caused by abnormal cilia and flagella. Cilia are microscopic, finger-like projections that stick out from the surface of cells. They are found in the linings of the airway, the reproductive system, and other organs and tissues. Flagella are tail-like structures, similar to cilia, that propel sperm cells forward.

Primary ciliary dyskinesia is an autosomal recessive disorder resulting from loss of normal ciliary function. Kartagener (pronounced KART-agayner) syndrome is characterized by the combination of primary ciliary dyskinesia and situs inversus, and occurs in approximately half of patients with ciliary dyskinesia. Since normal nodal ciliary movement in the embryo is required for normal visceral asymmetry, absence of normal ciliary movement results in a lack of definitive patterning; thus, random chance alone appears to determine whether the viscera take up the normal or reversed left-right position during embryogenesis. This explains why approximately 50% of patients, even within the same family, have situs inversus (Afzelius, 1976; El Zein et al., 2003). For a general description and a discussion of genetic heterogeneity of primary ciliary dyskinesia and Kartagener syndrome, see CILD1 (244400).

Three M syndrome is characterized by severe pre- and postnatal growth deficiency (final height 5-6 SD below the mean; i.e., 120-130 cm), characteristic facies, and normal intelligence. Additional features of three M syndrome include short broad neck, prominent trapezii, deformed sternum, short thorax, square shoulders, winged scapulae, hyperlordosis, short fifth fingers, prominent heels, and loose joints. Males with three M syndrome have hypogonadism and occasionally hypospadias.

Epidermolysis bullosa simplex (EBS) is characterized by fragility of the skin (and mucosal epithelia in some instances) that results in non-scarring blisters and erosions caused by minor mechanical trauma. EBS is distinguished from other types of epidermolysis bullosa (EB) or non-EB skin fragility syndromes by the location of the blistering in relation to the dermal-epidermal junction. In EBS, blistering occurs within basal keratinocytes. The severity of blistering ranges from limited to hands and feet to widespread involvement. Additional features can include hyperkeratosis of the palms and soles (keratoderma), nail dystrophy, milia, and hyper- and/or hypopigmentation. Rare EBS subtypes have been associated with additional clinical features including pyloric atresia, muscular dystrophy, cardiomyopathy, and/or nephropathy.

Congenital alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV) is characterized histologically by failure of formation and ingrowth of alveolar capillaries that then do not make contact with alveolar epithelium, medial muscular thickening of small pulmonary arterioles with muscularization of the intraacinar arterioles, thickened alveolar walls, and anomalously situated pulmonary veins running alongside pulmonary arterioles and sharing the same adventitial sheath. Less common features include a reduced number of alveoli and a patchy distribution of the histopathologic changes. The disorder is associated with persistent pulmonary hypertension of the neonate and shows varying degrees of lability and severity (Boggs et al., 1994). Affected infants present with respiratory distress resulting from pulmonary hypertension in the early postnatal period, and the disease is uniformly fatal within the newborn period (Vassal et al., 1998). Additional features of ACDMPV include multiple congenital anomalies affecting the cardiovascular, gastrointestinal, genitourinary, and musculoskeletal systems, as well as disruption of the normal right-left asymmetry of intrathoracic or intraabdominal organs (Sen et al., 2004).

Primary ciliary dyskinesia-14 (CILD14) is an autosomal recessive disorder characterized by recurrent respiratory infections associated with defects in ciliary inner dynein arms and axonemal disorganization (Merveille et al., 2011). For a general phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

Primary ciliary dyskinesia-15 (CILD15) is an autosomal recessive disorder characterized by recurrent respiratory infections associated with defects in ciliary inner dynein arms and axonemal disorganization (summary by Becker-Heck et al., 2011). For a general phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

SUCLG1-related mitochondrial DNA (mtDNA) depletion syndrome, encephalomyopathic form with methylmalonic aciduria is characterized in the majority of affected newborns by hypotonia, muscle atrophy, feeding difficulties, and lactic acidosis. Affected infants commonly manifest developmental delay / cognitive impairment, growth retardation / failure to thrive, hepatopathy, sensorineural hearing impairment, dystonia, and hypertonia. Notable findings in some affected individuals include hypertrophic cardiomyopathy, epilepsy, myoclonus, microcephaly, sleep disturbance, rhabdomyolysis, contractures, hypothermia, and/or hypoglycemia. Life span is shortened, with median survival of 20 months.

Congenital myopathy-11 (CMYO11) is an autosomal recessive skeletal muscle disorder characterized clinically by severe hypotonia apparent at birth, resulting in early feeding problems, motor delay, and walking difficulties. However, the course of the disease is nonprogressive: most affected individuals achieve independent ambulation and tend to show improvement of muscle weakness throughout childhood and early adulthood. There is no respiratory or cardiac involvement; cognitive development is normal. Muscle biopsy may show rare centralized nuclei, type 1 fiber hypotrophy, and type 1 fiber predominance, suggestive of a pathologic diagnosis of congenital fiber-type disproportion (CFTD). However, the findings on skeletal muscle biopsy may be nonspecific (Muhammad et al., 2013). For a discussion of genetic heterogeneity of congenital myopathy, see CMYO1A (117000).

Encephalopathy due to defective mitochondrial and peroxisomal fission-1 (EMPF1) is characterized by delayed psychomotor development and hypotonia that may lead to death in childhood. Many patients develop refractory seizures, consistent with an epileptic encephalopathy, and thereafter show neurologic decline. The age at onset, features, and severity are variable, and some patients may not have clinical evidence of mitochondrial or peroxisomal dysfunction (summary by Sheffer et al., 2016; Fahrner et al., 2016). Genetic Heterogeneity of Encephalopathy Due to Defective Mitochondrial And Peroxisomal Fission See also EMPF2 (617086), caused by mutation in the MFF gene (614785) on chromosome 2q36.

Hereditary sensory and autonomic neuropathy type VI (HSAN6) is a severe autosomal recessive disorder characterized by neonatal hypotonia, respiratory and feeding difficulties, lack of psychomotor development, and autonomic abnormalities including labile cardiovascular function, lack of corneal reflexes leading to corneal scarring, areflexia, and absent axonal flare response after intradermal histamine injection (summary by Edvardson et al., 2012). For a discussion of genetic heterogeneity of hereditary sensory and autonomic neuropathy, see HSAN1 (162400).

Primary ciliary dyskinesia-18 (CILD18) is an autosomal recessive disorder characterized by early infantile onset of recurrent sinopulmonary infections due to ciliary dysfunction and impaired airway clearance. Males are infertile and about half of patients have situs inversus. Electron microscopy of cilia shows a defect of the outer and inner dynein arms and impaired ciliary function (summary by Horani et al., 2012).

Primary ciliary dyskinesia-21 (CILD21) is an autosomal recessive ciliopathy characterized by infantile onset of chronic sinopulmonary infections resulting from abnormal ciliary function. Electron microscopy of respiratory epithelial cells shows normal outer and inner dynein arms, but absence of nexin links and defects in the nexin-dynein regulatory complex (N-DRC). Video microscopy of patient cilia shows an increased beat frequency with decreased bending amplitude (summary by Wirschell et al., 2013). For a phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

Primary ciliary dyskinesia-22 (CILD22) is an autosomal recessive disorder caused by defective structure and function of cilia or flagella. Ciliary dysfunction causes respiratory distress in term neonates, impaired mucociliary clearance, chronic cough, sinusitis, bronchiectasis, and male infertility. Defective motility of embryonic nodal cilia leads to situs abnormalities in about 50% of patients. CILD22 is characterized by defects of the inner and outer dynein arms (summary by Zariwala et al., 2013). For a phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

Primary ciliary dyskinesia-23 is an autosomal recessive disorder resulting from defective ciliary motility. Affected individuals have respiratory distress and recurrent upper and lower airway infections, and they often develop bronchiectasis. About 50% of patients have situs inversus or laterality defects. Ultrastructural analysis of respiratory cilia shows defects in the outer dynein arm (summary by Hjeij et al., 2013). For a phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see 244400.

Primary ciliary dyskinesia-24 is an autosomal recessive disorder resulting from defects of motile cilia. It is characterized clinically by sinopulmonary infection and subfertility; situs inversus is not observed. Ultrastructural examination of mutant cilia shows defects of the central microtubule complex and radial spokes (summary by Kott et al., 2013). For a phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see 244400.

Primary ciliary dyskinesia-25 is an autosomal recessive disorder caused by defective ciliary movement. Affected individuals have recurrent upper and lower airway disease, bronchiectasis, and decreased fertility. About half of patients show laterality defects, including situs inversus totalis. Respiratory cilia from patients show defects in the inner and outer dynein arms (summary by Tarkar et al., 2013). For a general phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see 244400.

Primary ciliary dyskinesia-26 is an autosomal recessive disorder caused by defective ciliary movement. Affected individuals have neonatal respiratory distress, recurrent upper and lower airway disease, and bronchiectasis. About half of patients show laterality defects, including situs inversus totalis. Respiratory cilia from patients show defects in the inner and outer dynein arms (summary by Austin-Tse et al., 2013). For a general phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see 244400.

Primary ciliary dyskinesia-27 is an autosomal recessive disorder caused by defective ciliary movement. Affected individuals have neonatal respiratory distress, recurrent upper and lower airway disease, and bronchiectasis. Respiratory cilia from patients show defects in the inner dynein arms and nexin links. Situs inversus has not been reported in these patients (summary by Austin-Tse et al., 2013). For a general phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see 244400.

Primary ciliary dyskinesia-28 (CILD28) is an autosomal recessive disorder caused by defective ciliary movement. Affected individuals have recurrent upper and lower airway disease, bronchiectasis, and decreased fertility. About half of patients show laterality defects, including situs inversus. Respiratory cilia from patients show defects in both the inner and outer dynein arms (summary by Knowles et al., 2013). For a general phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

Desbuquois dysplasia (DBQD) is an autosomal recessive chondrodysplasia belonging to the multiple dislocation group and characterized by severe prenatal and postnatal growth retardation (stature less than -5 SD), joint laxity, short extremities, and progressive scoliosis. The main radiologic features are short long bones with metaphyseal splay, a 'Swedish key' appearance of the proximal femur (exaggerated trochanter), and advanced carpal and tarsal bone age with a delta phalanx (summary by Huber et al., 2009). Desbuquois dysplasia is clinically and radiographically heterogeneous, and had been classified into 2 types based on the presence (type 1) or absence (type 2) of characteristic hand anomalies, including an extra ossification center distal to the second metacarpal, delta phalanx, bifid distal thumb phalanx, and dislocation of the interphalangeal joints (Faivre et al., 2004). However, patients with and without these additional hand anomalies have been reported to have mutations in the same gene (see, e.g., CANT1); thus, these features are not distinctive criteria to predict the molecular basis of DBQD (Furuichi et al., 2011). In addition, Kim et al. (2010) described another milder variant of DBQD with almost normal outwardly appearing hands, but significant radiographic changes, including short metacarpals, elongated phalanges, and remarkably advanced carpal bone age. However, there is no accessory ossification center distal to the second metacarpal, and patients do not have thumb anomalies. Similar changes occur in the feet. These patients also tend to develop precocious osteoarthritis of the hand and spine with age. This phenotype is sometimes referred to as the 'Kim variant' of DBQD (Furuichi et al., 2011). Genetic Heterogeneity of Desbuquois Dysplasia DBQD2 (615777) is caused by mutation in the XYLT1 gene (608124) on chromosome 16p12. Two unrelated patients with immunodeficiency-23 (IMD23; 615816), due to mutation in the PGM3 gene (172100), were reported to have skeletal features reminiscent of DBQD.

Desbuquois dysplasia, which belongs to the multiple dislocation group of disorders, is characterized by dislocations of large joints, severe pre- and postnatal growth retardation, joint laxity, and flat face with prominent eyes. Radiologic features include short long bones with an exaggerated trochanter that gives a 'monkey wrench' appearance to the proximal femur, and advanced carpal and tarsal ossification (summary by Bui et al., 2014). For a discussion of genetic heterogeneity of Desbuquois dysplasia, see DBQD1 (251450).

Spinal muscular atrophy with congenital bone fractures is an autosomal recessive severe neuromuscular disorder characterized by onset of severe hypotonia with fetal hypokinesia in utero. This results in congenital contractures, consistent with arthrogryposis multiplex congenita, and increased incidence of prenatal fracture of the long bones. Affected infants have difficulty breathing and feeding and often die in the first days or months of life (summary by Knierim et al., 2016). For a discussion of genetic heterogeneity of spinal muscular atrophy with congenital bone fractures, see SMABF1 (616866).

Spinal muscular atrophy with congenital bone fractures is an autosomal recessive severe neuromuscular disorder characterized by onset of severe hypotonia with fetal hypokinesia in utero. This results in congenital contractures, consistent with arthrogryposis multiplex congenita, and increased incidence of prenatal fracture of the long bones. Affected infants have difficulty breathing and feeding and often die in the first days or months of life (summary by Knierim et al., 2016). Genetic Heterogeneity of Spinal Muscular Atrophy With Congenital Bone Fractures See also SMABF2 (616867), caused by mutation in the ASCC1 gene (614215) on chromosome 10q22.

Primary ciliary dyskinesia-32 is an autosomal recessive disorder caused by defective structure and function of cilia. Ciliary dysfunction causes respiratory distress in term neonates, impaired mucociliary clearance, chronic respiratory infections, bronchiectasis, and infertility. The ciliary defect affects the central pair complex and radial spokes of the 9+2 motile cilia; affected individuals do not have situs abnormalities (summary by Jeanson et al., 2015). For a general phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

Congenital myasthenic syndrome-18 (CMS18) is an autosomal dominant presynaptic neuromuscular disorder characterized by early-onset muscle weakness and easy fatigability associated with delayed psychomotor development and ataxia (summary by Shen et al., 2014). For a discussion of genetic heterogeneity of CMS, see CMS1A (601462).

Congenital myasthenic syndrome associated with AChR deficiency is a disorder of the postsynaptic neuromuscular junction (NMJ) clinically characterized by early-onset muscle weakness with variable severity. Electrophysiologic studies show low amplitude of the miniature endplate potential (MEPP) and current (MEPC) resulting from deficiency of AChR at the endplate. Treatment with cholinesterase inhibitors or amifampridine may be helpful (summary by Engel et al., 2015). For a discussion of genetic heterogeneity of CMS, see CMS1A (601462).

Arboleda-Tham syndrome (ARTHS) is an autosomal dominant disorder with the core features of impaired intellectual development, speech delay, microcephaly, cardiac anomalies, and gastrointestinal complications (summary by Kennedy et al., 2019).

CLIFAHDD is a congenital disorder characterized by congenital contractures of the limbs and face, resulting in characteristic facial features, hypotonia, and variable degrees of developmental delay. All reported cases have occurred de novo (summary by Chong et al., 2015).

Primary ciliary dyskinesia-35 (CILD35) is an autosomal recessive disorder characterized by recurrent upper and lower respiratory infections due to defective ciliary function. Examination of respiratory cilia shows lack of outer dynein arms (ODAs) and immotile cilia. Some patients may have laterality defects (summary by Wallmeier et al., 2016). For a phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

Primary ciliary dyskinesia-34 (CILD34) is an autosomal recessive disorder characterized by childhood onset of recurrent sinopulmonary infections due to impaired ciliary function. Affected males are infertile due to impaired sperm function and viability. Laterality defects have not been observed in this type of CILD (summary by El Khouri et al., 2016). For a general phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

CILD36 is an X-linked recessive disorder characterized by chronic airway disease and recurrent sinopulmonary infections beginning in childhood and caused by defective ciliary function. Affected individuals also have infertility due to defective sperm flagella. About half of patients have laterality defects due to ciliary dysfunction at the embryonic node (summary by Paff et al., 2017). For a phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

Junctional epidermolysis bullosa-7 with interstitial lung disease and nephrotic syndrome (JEB7), also known as ILNEB, is an autosomal recessive multiorgan disorder that includes congenital interstitial lung disease, nephrotic syndrome, and epidermolysis bullosa. The respiratory and renal features predominate, and lung involvement accounts for the lethal course of the disease (summary by Has et al., 2012).

Birk-Landau-Perez syndrome (BILAPES) is an autosomal recessive syndromic developmental disorder characterized by global developmental delay apparent from infancy or early childhood. Some patients have developmental regression with loss of speech and motor skills, whereas other patients never achieve these milestones. More variable features may include hypotonia, poor overall growth, ataxia, dystonia, abnormal eye movements, and renal insufficiency (Perez et al., 2017; Kleyner et al., 2022).

Generalized arterial calcification of infancy (GACI) is characterized by infantile onset of widespread arterial calcification and/or narrowing of large and medium-sized vessels resulting in cardiovascular findings (which can include heart failure, respiratory distress, edema, cyanosis, hypertension, and/or cardiomegaly). Additional findings can include typical skin and retinal manifestations of pseudoxanthoma elasticum (PXE), periarticular calcifications, development of rickets after infancy, cervical spine fusion, and hearing loss. While mortality in infancy is high, survival into the third and fourth decades has occurred.

Shwachman-Diamond syndrome (SDS) is characterized by: exocrine pancreatic dysfunction with malabsorption, malnutrition, and growth failure; hematologic abnormalities with single- or multilineage cytopenias and susceptibility to myelodysplasia syndrome (MDS) and acute myelogeneous leukemia (AML); and bone abnormalities. In almost all affected children, persistent or intermittent neutropenia is a common presenting finding, often before the diagnosis of SDS is made. Short stature and recurrent infections are common.

Ehlers-Danlos syndrome classic-like-2 (EDSCLL2) is characterized by severe joint and skin laxity, osteoporosis involving the hips and spine, osteoarthritis, soft redundant skin that can be acrogeria-like, delayed wound healing with abnormal atrophic scarring, and shoulder, hip, knee, and ankle dislocations. Variable features include gastrointestinal and genitourinary manifestations, such as bowel rupture, gut dysmotility, cryptorchidism, and hernias; vascular complications, such as mitral valve prolapse and aortic root dilation; and skeletal anomalies (Blackburn et al., 2018). For a discussion of genetic heterogeneity of classic-like Ehlers-Danlos syndrome, see 606408. For a discussion of the classification of EDS, see 130000.

Alacrima, achalasia, and impaired intellectual development syndrome (AAMR) is an autosomal recessive disorder characterized by onset of these 3 main features at birth or in early infancy. More variable features include hypotonia, gait abnormalities, anisocoria, and visual or hearing deficits. The disorder shows similarity to the triple A syndrome (231550), but patients with AAMR do not have adrenal insufficiency (summary by Koehler et al., 2013). See also 300858 for a phenotypically similar disorder that shows X-linked inheritance.

Zellweger spectrum disorder (ZSD) is a phenotypic continuum ranging from severe to mild. While individual phenotypes (e.g., Zellweger syndrome [ZS], neonatal adrenoleukodystrophy [NALD], and infantile Refsum disease [IRD]) were described in the past before the biochemical and molecular bases of this spectrum were fully determined, the term "ZSD" is now used to refer to all individuals with a defect in one of the ZSD-PEX genes regardless of phenotype. Individuals with ZSD usually come to clinical attention in the newborn period or later in childhood. Affected newborns are hypotonic and feed poorly. They have distinctive facies, congenital malformations (neuronal migration defects associated with neonatal-onset seizures, renal cysts, and bony stippling [chondrodysplasia punctata] of the patella[e] and the long bones), and liver disease that can be severe. Infants with severe ZSD are significantly impaired and typically die during the first year of life, usually having made no developmental progress. Individuals with intermediate/milder ZSD do not have congenital malformations, but rather progressive peroxisome dysfunction variably manifest as sensory loss (secondary to retinal dystrophy and sensorineural hearing loss), neurologic involvement (ataxia, polyneuropathy, and leukodystrophy), liver dysfunction, adrenal insufficiency, and renal oxalate stones. While hypotonia and developmental delays are typical, intellect can be normal. Some have osteopenia; almost all have ameleogenesis imperfecta in the secondary teeth.

Primary ciliary dyskinesia-38 is an autosomal recessive disorder characterized by chronic airway disease and recurrent sinopulmonary infections beginning in infancy and caused by defective ciliary function. Affected individuals often have neonatal respiratory distress and may later have infertility. About half of patients have laterality defects due to ciliary dysfunction in early embryonic development (summary by Fassad et al., 2018 and Hoben et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

CAFDADD is a multisystemic developmental disorder with variable cardiac and digital anomalies and facial dysmorphism. Some patients may have seizures and ocular/aural abnormalities (Tokita et al., 2018).

A rare fatal inborn error of metabolism disorder with characteristics of respiratory distress and severe hypotonia at birth, severe global developmental delay, early-onset intractable seizures, myopathic facies with craniofacial dysmorphism (trigonocephaly/progressive microcephaly, low anterior hairline, arched eyebrows, hypotelorism, strabismus, small nose, prominent philtrum, thin upper lip, high-arched palate, micrognathia, malocclusion), severe, congenital flexion joint contractures and elevated serum creatine kinase levels. Scoliosis, optic atrophy, mild hepatomegaly, and hypoplastic genitalia may also be associated. There is evidence the disease is caused by homozygous or compound heterozygous mutation in the DPM2 gene on chromosome 9q34.

Neurodevelopmental disorder with central and peripheral motor dysfunction (NEDCPMD) is an autosomal recessive neurologic disorder with a highly variable phenotype. At the severe end of the spectrum, patients may have hypotonia apparent from birth, necessitating mechanical respiration and tube-feeding, and global developmental delay with absence of reaction to touch and no eye contact. At the mild end of the spectrum, patients may present with infantile-onset progressive ataxia and demyelinating peripheral neuropathy. The disorder is caused by mutation in the NFASC gene, which has several neuronal- and glial-specific transcripts. The variable clinical phenotype may be caused by several factors, including the severity of the mutation, the selective involvement of distinct isoforms by pathogenic variants, and the presence of genetic modifiers (summary by Monfrini et al., 2019).

Susceptibility to acute infection-induced encephalopathy-9 (IIAE9) is an autosomal recessive disorder characterized by episodic acute neurodegeneration and developmental regression associated with infections and febrile illness. Patients present in the first months or years of life, often after normal or only mildly delayed early development. Some patients may have partial recovery between episodes, such as transient ataxia, but the overall disease course is progressive, resulting in global developmental delay, abnormal movements, refractory seizures, microcephaly, and cerebellar atrophy (summary by Fichtman et al., 2019). For a discussion of genetic heterogeneity of susceptibility to acute infection-induced encephalopathy, see 610551.

Neurodevelopmental disorder with microcephaly, arthrogryposis, and structural brain anomalies (NEDMABA) is an autosomal recessive disorder characterized by severe global developmental delay, usually with hypotonia and absence of spontaneous movements other than head control, impaired intellectual development with absent speech, distal contractures, progressive microcephaly, dysmorphic features, and distal skeletal abnormalities, such as rocker-bottom feet and clenched hands with camptodactyly. Brain imaging tends to show a simplified gyral pattern of the cerebral cortex, delayed myelination, thin corpus callosum, and hypoplasia of the brainstem and cerebellum. The disorder may be complicated by feeding and/or breathing difficulties, often resulting in death in infancy (summary by Magini et al., 2019).

Primary ciliary dyskinesia-43 (CILD43) is a disorder characterized by a defect in motile cilia and ciliary clearance resulting in the onset of respiratory insufficiency soon after birth, and associated with recurrent upper and lower respiratory infections with chronic progressive lung disease. Patients with this disorder also develop significant obstructive hydrocephalus requiring shunting in infancy, although adult onset of neurologic symptoms may occur. Other more variable features include infertility and about a 50% chance of situs inversus or other left-right asymmetry defects. The disorder is considered to be a type of ciliopathy known as 'reduced generation of multiple motile cilia' (RGMC) (summary by Wallmeier et al., 2019). For a discussion of genetic heterogeneity of primary ciliary dyskinesia, CILD1 (244400).

Primary ciliary dyskinesia-44 (CILD44) is an autosomal recessive disorder characterized by recurrent sinopulmonary infections resulting from defective mucociliary clearance. Affected individuals have onset of symptoms in infancy or early childhood, and the repetitive nature of the disorder results in bronchiectasis. Although respiratory epithelial cell motile cilia are shorter than normal and overall ciliary motion is decreased, nasal nitric oxide, radial ciliary structure, and ciliary beat frequency are normal. In addition, patients do not have situs inversus (summary by Chivukula et al., 2020). For a phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

Neurodevelopmental disorder with hypotonia, neonatal respiratory insufficiency, and thermodysregulation (NEDHRIT) is a severe autosomal recessive disorder characterized by neonatal respiratory distress, poor feeding, and impaired global development. Affected individuals are unable to walk or speak and have poor or absent eye contact. Some patients may develop seizures (summary by Wagner et al., 2020).

Nabais Sa-de Vries syndrome type 1 (NSDVS1) is characterized by global developmental delay apparent from infancy, variable behavioral abnormalities, microcephaly, and dysmorphic facial features, including round face, small palpebral fissures, highly arched eyebrows, and short nose. The severity is variable (summary by Nabais Sa et al., 2020).

CSGALNACT1 deficiency is characterized by mild skeletal dysplasia, joint hypermobility, and advanced bone age. Shortness of long bones is evident prenatally, and patients exhibit short stature and relative macrocephaly. Advanced carpotarsal bone age and monkey-wrench appearance of the femur observed in infancy may disappear with age (Mizumoto et al., 2020).

Neurodevelopmental disorder with seizures, hypotonia, and brain imaging abnormalities (NEDSHBA) is an autosomal recessive neurodevelopmental disorder characterized by global developmental delay, severe to profound intellectual impairment, early-onset refractory seizures, hypotonia, failure to thrive, and progressive microcephaly. Brain imaging shows cerebral atrophy, thin corpus callosum, and myelination defects. Death in childhood may occur (summary by Marafi et al., 2020).

Spondylometaphyseal dysplasia with corneal dystrophy (SMDCD) is characterized by short stature due to short proximal and distal long bones. Affected individuals also exhibit narrow thorax with pulmonary hypoplasia and respiratory failure, as well as corneal dystrophy. Severe developmental delay has been observed (Ben-Salem et al., 2018).

Arthrogryposis multiplex congenita-5 (AMC5) is an autosomal recessive disorder characterized by severe joint contractures apparent at birth. Affected individuals usually have hypertonia and abnormal movements suggestive of dystonia, as well as feeding and/or breathing difficulties. More variable features may include poor overall growth, strabismus, dysmorphic facies, and global developmental delay with impaired speech (summary by Kariminejad et al., 2017).

DEEAH syndrome is an autosomal recessive multisystemic disorder with onset in early infancy. Affected individuals usually present in the perinatal period with respiratory insufficiency, apneic episodes, and generalized hypotonia. The patients have failure to thrive and severely impaired global development with poor acquisition of motor, cognitive, and language skills. Other common features include endocrine, pancreatic exocrine, and autonomic dysfunction, as well as hematologic disturbances, mainly low hemoglobin. Patients also have dysmorphic and myopathic facial features. Additional more variable features include seizures, undescended testes, and distal skeletal anomalies. Death in early childhood may occur (summary by Schneeberger et al., 2020).

Neurodevelopmental disorder with dysmorphic facies, impaired speech, and hypotonia (NEDDISH) is an autosomal recessive disorder characterized by global developmental delay and mildly to severely impaired intellectual development with poor speech and language acquisition. Some patients may have early normal development with onset of the disorder in the first years of life. More variable neurologic abnormalities include hypotonia, seizures, apnea, mild signs of autonomic or peripheral neuropathy, and autism. Aside from dysmorphic facial features and occasional findings such as scoliosis or undescended testes, other organ systems are not involved (summary by Schneeberger et al., 2020).

Myopathy, epilepsy, and progressive cerebral atrophy (MEPCA) is a severe autosomal recessive disorder with onset in utero or at birth. Affected individuals have hypotonia with respiratory or feeding difficulties apparent from birth and often associated with contractures of the large joints. There is little spontaneous movement: skeletal muscle biopsy and electrophysiologic studies are consistent with a myopathy or myasthenic disorder. Patients also develop refractory seizures with burst-suppression pattern or hypsarrhythmia on EEG. Brain imaging shows progressive cerebral atrophy and myelination defects. All patients reported to date died within the first year of life (summary by Schorling et al., 2017).

Mitochondrial complex IV deficiency nuclear type 10 (MC4DN10) is an autosomal recessive multisystem metabolic disorder characterized by the onset of severe symptoms soon after birth. Affected infants have respiratory and neurologic distress, metabolic lactic acidosis, and dysmorphic features, including microphthalmia. Death occurs in early infancy. Postmortem examination has demonstrated systemic involvement with hepatomegaly, hypertrophic cardiomyopathy, renal hypoplasia, and adrenal hyperplasia. There is also abnormal brain myelination and cavitating brain lesions. Patient tissues show decreased levels and activity of mitochondrial respiratory complex IV (summary by Weraarpachai et al., 2012). For a discussion of genetic heterogeneity of mitochondrial complex IV (cytochrome c oxidase) deficiency, see 220110.

Combined oxidative phosphorylation deficiency-51 (COXPD51) is an autosomal recessive disorder characterized by a Leigh syndrome phenotype (see 256000). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Mitochondrial complex IV deficiency nuclear type 18 (MC4DN18) is an autosomal recessive metabolic disorder that primarily affects skeletal muscle tissue. Affected individuals present in infancy with hypotonia, limb muscle weakness, and high-arched palate. The severity of the disorder is variable: some patients may only have gait difficulties, whereas others may also have significant respiratory insufficiency and cardiomyopathy. Death in infancy has been reported. Patient skeletal muscle shows decreased levels and activity of mitochondrial respiratory complex IV (Inoue et al., 2019). For a discussion of genetic heterogeneity of mitochondrial complex IV (cytochrome c oxidase) deficiency, see 220110.

Developmental and epileptic encephalopathy-96 (DEE96) is characterized by onset of seizures in the first days or weeks of life. Affected infants have tonic or myoclonic seizures associated with burst-suppression pattern on EEG. They also have hypotonia with respiratory insufficiency that may result in premature death. Those that survive have profound developmental delay and persistent seizures (summary by Suzuki et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Short-rib thoracic dysplasia-21 (SRTD21) is characterized by rhizomelic limb shortening with bowing of long bones and metaphyseal abnormalities, narrow chest with short broad ribs, and trident pelvis. Other features include hypotonia and global developmental delay, with corpus callosum hypoplasia and cerebellar vermis abnormalities on brain imaging, which may show the 'molar tooth' sign (Hammarsjo et al., 2017). For a general phenotypic description and discussion of genetic heterogeneity of SRTD, see SRTD1 (208500). Mutation in the KIAA0753 gene also causes orofaciodigital syndrome (OFD15; 617127) and Joubert syndrome (JBTS28; 619476), phenotypes with features overlapping those of SRTD21.

Neurodevelopmental disorder with hypotonia and dysmorphic facies (NEDHYDF) is characterized by global developmental delay and hypotonia apparent from birth. Affected individuals have variably impaired intellectual development, often with speech delay and delayed walking. Seizures are generally not observed, although some patients may have single seizures or late-onset epilepsy. Most patients have prominent dysmorphic facial features. Additional features may include congenital cardiac defects (without arrhythmia), nonspecific renal anomalies, joint contractures or joint hyperextensibility, dry skin, and cryptorchidism. There is significant phenotypic variability in both the neurologic and extraneurologic manifestations (summary by Tan et al., 2022).

Lymphatic malformation-12 (LMPHM12) is characterized by abnormalities in the development and function of major truncal lymphatic vessels, causing nonimmune hydrops fetalis that results in stillbirth in some cases. Other affected individuals experience postnatal subcutaneous lymphedema and chylothorax, with pleural and pericardial effusions and ascites (Byrne et al., 2022). For a general phenotypic description and discussion of genetic heterogeneity of lymphatic malformation, see LMPHM1 (153100).

Diaphragmatic hernia-4 with cardiovascular defects (DIH4) is an autosomal recessive congenital anomaly syndrome characterized by the presence of diaphragmatic hernia or eventration apparent at birth. Affected infants have associated pulmonary hypoplasia and respiratory insufficiency resulting in death in infancy. Most also have variable cardiovascular defects, including aortopulmonary window or conotruncal anomalies. Dysmorphic facial features and mild distal limb anomalies are sometimes observed (Beecroft et al., 2021). For a discussion of genetic heterogeneity of congenital diaphragmatic hernia (CDH), see DIH1 (142340).

ARCND2B is characterized by the typical features of auriculocondylar syndrome, including the pathognomonic question mark ears, consisting of a variable degree of clefting between the helix and earlobe, as well as hypoplasia of the mandibular condyle, temporomandibular joint abnormalities, micrognathia, microstomia, glossoptosis, and a round facial appearance with prominent cheeks. Patients have difficulty chewing, respiratory abnormalities, snoring, and obstructive and central apneas. In addition, they experience severe gastrointestinal problems, including feeding difficulties with failure to thrive, gastroesophageal reflux, and chronic constipation, and male patients show macropenis whereas female patients may exhibit clitoromegaly (summary by Leoni et al., 2016). Heterozygous mutation in the PLCB4 gene also causes an autosomal dominant form of auriculocondylar syndrome (see ARCND2A, 614669). For a discussion of genetic heterogeneity of auriculocondylar syndrome, see ARCND1 (602483).