GM1-generalized gangliosidosis variant with cardiomegaly.

A female infant with generalized GM1-gangliosidosis differing in several aspects from previously reported cases is described. Clinically she is the first case to have cardiomegaly, unilateral congenitial dislocation of the hip and normal facial appearance. She had a higher residual leucocyte β-galactosidase activity towards two synthetic substrates, namely p-nitrophenyl-β-D-galactoside (PNP-β-gal) and 4-methylumbelliferyl-β-D-galactoside (MU-β-gal) than in previously reported cases. Total β-hexosaminidase activity was raised in cultured fibroblasts, leucocytes, brain, kidneys and liver of the patient, and in fibroblasts from the parents. The parents' leucocytes had normal β-galactosidase activity towards PNP-β-gal but slightly reduced activity towards MU-β-gal. The parents' cultured fibroblast enzyme, however, had moderately low activities towards both substrates. It is suggested that she may represent a genetic variant of generalized GM1-gangliosidosis and that assay of leucocyte β-galactosidase activity should be added to the list of investigations for infantile cardiomegaly of unknown origin.