The enzymatic diagnosis of GM1 gangliosidosis, including the diagnosis of heterozygosity, requires a microassay of GM1 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 GM1 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 GM1 gangliosidosis. Thus, this assay can be used for the diagnosis, rather than the usual assays employing radioactive or artificial substrates.
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