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Type 3 is a less frequent form of GM1 gangliosidosis compared to infantile type 1 disease but the exact prevalence, although unknown, is likely to be underestimated. About 70 cases have been reported to date. Overall prevalence at birth of GM1 gangliosidosis is estimated to be approximately 1:100,000 to 200,000 live births. Most reported cases are in patients of Japanese origin.

Marked variability of clinical signs and age of onset has been reported. Patients generally show slowly progressive dementia, dysarthria, dystonia, short stature, mild vertebral anomalies and ataxia. Eye movements are normal.

GM1 gangliosidosis is caused by mutations in the GLB1gene (3p22.3) coding for beta-galactosidase.

Diagnosis is clinically suggested by dystonia and slurred speech, usually detected at school age. Biochemical and/or molecular genetic tests confirm the diagnosis.

Differential diagnosis includes mucopolysaccharidoses, sphingolipidoses and oligosaccharidoses (see these terms).

Prenatal diagnosis can be performed by analysis of beta-galactosidase activity and/or by GLB1 molecular analysis in either chorionic villus (CV) cells or amniotic fluid cells if mutations are identified in an index case.

GM1 gangliosidosis is an autosomal recessive disease. Genetic counseling should be provided to affected families.

Treatment for patients with GM1 gangliosidosis is symptomatic and supportive.

Prognosis is variable.