Application of a G_M1 ganglioside β-galactosidase microassay method to diagnosis of G_M1 gangliosidosis

The enzymatic diagnosis of G_M1 gangliosidosis, including the diagnosis of heterozygosity, requires a microassay of G_M1 ganglioside β-galactosidase activity in lymphocytes and cultured skin fibroblasts. We have adopted high-performance liquid chromatography (HPLC) to the assay of this enzyme and can measure the activity in crude samples fluorometrically. Reaction conditions were examined to determine those optimal for the assay of G_M1 ganglioside β-galactosidase activity in lymphocyte and skin fibroblast homogenates. Under these optimal conditions, reduced enzymatic activities could be detected in lymphocytes and cultured skin fibroblasts from three patients with G_M1 gangliosidosis. Thus, this assay can be used for the diagnosis, rather than the usual assays employing radioactive or artificial substrates.