Arylsulfatase A deficiency (also known as metachromatic leukodystrophy or MLD) is characterized by three clinical subtypes: late-infantile MLD, juvenile MLD, and adult MLD. Age of onset within a family is usually similar. The disease course may be from several years in the late-infantile-onset form to decades in the juvenile- and adult-onset forms. Late-infantile MLD. Onset is before age 30 months. Typical presenting findings include weakness, hypotonia, clumsiness, frequent falls, toe walking, and dysarthria. As the disease progresses, language, cognitive, and gross and fine motor skills regress. Later signs include spasticity, pain, seizures, and compromised vision and hearing. In the final stages, children have tonic spasms, decerebrate posturing, and general unawareness of their surroundings. Juvenile MLD. Onset is between age 30 months and 16 years. Initial manifestations include decline in school performance and emergence of behavioral problems, followed by gait disturbances. Progression is similar to but slower than in the late-infantile form. Adult MLD. Onset occurs after age 16 years, sometimes not until the fourth or fifth decade. Initial signs can include problems in school or job performance, personality changes, emotional lability, or psychosis; in others, neurologic symptoms (weakness and loss of coordination progressing to spasticity and incontinence) or seizures initially predominate. Peripheral neuropathy is common. Disease course is variable – with periods of stability interspersed with periods of decline – and may extend over two to three decades. The final stage is similar to earlier-onset forms.

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).

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).

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).

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.

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).

X-linked syndromic intellectual developmental disorder with pigmentary mosaicism and coarse facies (MRXSPF) is characterized by a phenotypic triad of severe developmental delay, coarse facial dysmorphisms, and Blaschkoid pigmentary mosaicism. Additional clinical features may include epilepsy, orthopedic abnormalities, hypotonia, and growth abnormalities. The disorder affects both males and females (Villegas et al., 2019; Diaz et al., 2020).

Telomere-related pulmonary fibrosis and/or bone marrow failure syndrome-8 (PFBMFT8) is an autosomal dominant disorder characterized by the onset of progressive pulmonary fibrosis in adulthood. Some affected individuals have signs of bone marrow failure, such as thrombocytopenia, or liver dysfunction, including hepatopulmonary syndrome. Other features of dyskeratosis congenita, including premature graying of the hair, may be observed. Telomeres are shortened compared to controls (Kelich et al., 2022). For a discussion of genetic heterogeneity of telomere-related pulmonary fibrosis and/or bone marrow failure, see PFBMFT1 (614742).