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GM1 gangliosidosis type 2
GM1 gangliosidosis type 2 is a clinically variable, infancy or childhood-onset form of GM1 gangliosidosis (see this term) characterized by normal early development and psychomotor regression between seven months and three years of age.
Type 2 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. Fewer than 50 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.
Patients with the childhood form of this disorder develop signs and symptoms of intermediate severity including locomotor disturbances, strabismus, muscle weakness, seizures, lethargy and lung infections. Compared to type 1, visceromegaly and skeletal anomalies are milder or may be absent. Macular cherry-red spots are infrequent. The course of the disorder is characterized by slower progression. Facial coarsening develops over time.
GM1 gangliosidosis is caused by mutations in the GLB1 gene (3p22.3) coding for beta-galactosidase.
Diagnosis is suggested by clinical signs, such as psychomotor regression and facial coarsening. Biochemical and/or 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.
Management and treatment
Treatment for patients with GM1 gangliosidosis is symptomatic and supportive.
Prognosis is poor with survival into mid-childhood or early adulthood.