OMIM ID:
GM1 Gangliosidosis
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Based on clinical manifestations, three types have been described: type I or infantile form, type II or late-infantile/juvenile form, and type III or adult/chronic form but all are due to mutations in the same gene. Only the infantile form has the typical cherry red spot in the macula but is present in only about 50% of infants. The corneal clouding is due to intracellular accumulations of mucopolysaccharides in corneal epithelium and keratan sulfate in keratocytes. Retinal ganglion cells also have accumulations of gangliosides. Decreased acuity, nystagmus, strabismus and retinal hemorrhages have been described.
Systemic Features
Infants with type I disease are usually hypotonic from birth but develop spasticity, psychomotor retardation, and hyperreflexia within 6 months. Early death from cardiopulmonary disease or infection is common. Hepatomegaly, coarse facial features, brachydactyly, and cardiomyopathy with valvular dysfunction are common. Dermal melanocytosis has also been described in infants in a pattern some have called Mongolian spots. Skeletal dysplasia is a feature and often leads to vertebral deformities and scoliosis. The ears are often large and low-set, the nasal bridge is depressed, the tongue is enlarged and frontal bossing is often striking. Hirsutism, coarse skin, short digits, and inguinal hernias are common.
The juvenile form, type II, has a later onset with psychomotor deterioration, seizures and skeletal changes apparent between 7 and 36 months and death in childhood. Visceral involvement and cherry-red spots are usually not present.
Type III, or adult form, is manifest later in the first decade or even sometime by the 4th decade. Symptoms and signs are more localized. Neurological signs are evident as dystonia or speech and gait difficulties. Dementia, parkinsonian signs, and extrapyramidal disease are late features. No hepatosplenomegaly, facial dysmorphism, or cherry red spots are present in most individuals. Lifespan may be normal in this type.
Genetics
Inheritance
This is an autosomal recessive lysosomal storage disease secondary to a mutations in GLB1 (3p21.33). It is allelic to Morquio B disease (MPS IVB) (253010). The mutations in the beta-galactosidase-1 gene result in intracellular accumulation of GM1 ganglioside, keratan sulfate, and oligosaccharides. The production of the enzyme varies among different mutations likely accounting for the clinical heterogeneity.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.