Normal serum β-galactosidase in juvenile GM1 gangliosidosis

Abstract GM1 gangliosidosis is a genetic disease with lysosomal β-galactosidase deficiency caused by mutations of the gene coding for this enzyme. However, apparently normal enzyme activity was found in plasma or serum from juvenile GM1 gangliosidosis patients homozygous for a mutation, R201C ( 201 Arg→Cys), after clotting for 30 min. This extracellular fluid finding is unusual in patients with primary and genetic deficiency of β-galactosidase. The serum enzyme activity became relatively low only after 312-hour clotting because its increase in normal controls was not observed in these patients. β-Galactosidase assay is not always reliable, particularly with serum or plasma as an enzyme source, for the diagnosis of hereditary β-galactosidase deficiency, unless it is conducted under well- controlled conditions.