Clinical course of GM1 gangliosidoses.

The GM1 gangliosidoses are clinically characterized by the combination of a degenerative process in the brain and of storage phenomena in extra-neural tissues, particularly in bones and visceral organs. Phenotypic variability is pronounced. "Classical" types, according to the age at onset, are infantile ("generalized"), juvenile, and adult forms. In rare variants, the degenerative process may be restricted to the basal ganglia and cause dystonia musculorum deformans, or it may cause infantile cardiomyopathy. Much of this variability may be explained by variable residual activities of the deficient beta-galactosidase towards various substrates.