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 kidney function to end-stage kidney disease (ESKD) usually occurs in men in the third to fifth decade. In middle age, most males successfully treated for ESKD 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; kidney failure, associated with ESKD 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 the neuronopathic phenotype, central nervous system (CNS) involvement (manifesting primarily as progressive cognitive deterioration), progressive airway disease, and cardiac disease usually results in death in the first or second decade of life. In those with the non-neuronopathic phenotype, the CNS is minimally or not affected. However, the effect of GAG accumulation on other organ systems can be severe. Survival into the early adult years with normal intelligence is common in the non-neuronopathic phenotype. Additional findings in neuronopathic and non-neuronopathic MPS II include: short stature, macrocephaly with or without communicating hydrocephalus, macroglossia, hoarse voice, conductive and sensorineural hearing loss, dysostosis multiplex, spinal stenosis, carpal tunnel syndrome, and hepatosplenomegaly.

Individuals with mucopolysaccharidosis type VII (MPS VII) can present perinatally with early demise, nonimmune hydrops fetalis, cholestatic jaundice, and hepatosplenomegaly, or in early childhood with developmental delay and characteristic musculoskeletal features (e.g., short neck, short-trunk short stature, pectus deformity, gibbus, and joint stiffness/contractures) and craniofacial features (e.g., macrocephaly, coarse hair, coarse facies, corneal clouding, and macroglossia). Skeletal survey shows features of dysostosis multiplex including thickened cortical bone, abnormal J-shaped sella turcica, paddle- or oar-shaped ribs, short, thickened clavicles, platyspondyly with anterior beaking of the lower thoracic and lumbar vertebrae, and proximal pointing of the metacarpals and metatarsals. Complications include developmental delay, intellectual disability, hepatosplenomegaly, spinal stenosis, recurrent otitis media, hearing loss, pulmonary disease, obstructive sleep apnea, hernias, feeding difficulties, and heart valve disease.

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).