Fabry disease is the most common of the lysosomal storage disorders and results from deficient activity of the enzyme alpha-galactosidase A (a-Gal A), leading to progressive lysosomal deposition of globotriaosylceramide and its derivatives in cells throughout the body. The classic form, occurring in males with less than 1% a-Gal A enzyme activity, usually has its onset in childhood or adolescence with periodic crises of severe pain in the extremities (acroparesthesia), the appearance of vascular cutaneous lesions (angiokeratomas), sweating abnormalities (anhidrosis, hypohidrosis, and rarely hyperhidrosis), characteristic corneal and lenticular opacities, and proteinuria. Gradual deterioration of renal function to end-stage renal disease (ESRD) usually occurs in men in the third to fifth decade. In middle age, most males successfully treated for ESRD develop cardiac and/or cerebrovascular disease, a major cause of morbidity and mortality. Heterozygous females typically have milder symptoms at a later age of onset than males. Rarely, females may be relatively asymptomatic throughout a normal life span or may have symptoms as severe as those observed in males with the classic phenotype. In contrast, late-onset forms occur in males with greater than 1% a-Gal A activity. Clinical manifestations include cardiac disease, which usually presents in the sixth to eighth decade with left ventricular hypertrophy, cardiomyopathy, arrhythmia, and proteinuria; renal failure, associated with ESRD but without the skin lesions or pain; or cerebrovascular disease presenting as stroke or transient ischemic attack.

Mucopolysaccharidosis type II (MPS II; also known as Hunter syndrome) is an X-linked multisystem disorder characterized by glycosaminoglycan (GAG) accumulation. The vast majority of affected individuals are male; on rare occasion heterozygous females manifest findings. Age of onset, disease severity, and rate of progression vary significantly among affected males. In those with early progressive disease, CNS involvement (manifest primarily by progressive cognitive deterioration), progressive airway disease, and cardiac disease usually result in death in the first or second decade of life. In those with slowly progressive disease, the CNS is not (or is minimally) affected, although the effect of GAG accumulation on other organ systems may be early progressive to the same degree as in those who have progressive cognitive decline. Survival into the early adult years with normal intelligence is common in the slowly progressing form of the disease. Additional findings in both forms of MPS II include: short stature; macrocephaly with or without communicating hydrocephalus; macroglossia; hoarse voice; conductive and sensorineural hearing loss; hepatosplenomegaly; dysostosis multiplex; spinal stenosis; and carpal tunnel syndrome.

Mucopolysaccharidosis type VII (MPS7) is an autosomal recessive lysosomal storage disease characterized by the inability to degrade glucuronic acid-containing glycosaminoglycans. The phenotype is highly variable, ranging from severe lethal hydrops fetalis to mild forms with survival into adulthood. Most patients with the intermediate phenotype show hepatomegaly, skeletal anomalies, coarse facies, and variable degrees of mental impairment (Shipley et al., 1993). MPS VII was the first autosomal mucopolysaccharidosis for which chromosomal assignment was achieved.

The Marshall-Smith syndrome (MRSHSS) is a malformation syndrome characterized by accelerated skeletal maturation, relative failure to thrive, respiratory difficulties, mental retardation, and unusual facies, including prominent forehead, shallow orbits, blue sclerae, depressed nasal bridge, and micrognathia (Adam et al., 2005).

Keutel syndrome (KTLS) is an autosomal recessive disorder characterized by multiple peripheral pulmonary stenoses, brachytelephalangy, inner ear deafness, and abnormal cartilage ossification or calcification (summary by Khosroshahi et al., 2014).

Autosomal recessive limb-girdle muscular dystrophy-21 (LGMDR21) is characterized by progressive limb-girdle weakness with age of onset ranging from congenital to adult. Muscle imaging shows a specific and selective pattern of fatty muscle degeneration (summary by Servian-Morilla et al., 2020). For a discussion of genetic heterogeneity of autosomal recessive LGMD, see LGMDR1 (253600).