Glycosidases in Normal Human Leukocytes and Abnormalities in GM1-Gangliosidosis

Abstract

Leukocyte enzyme assay is a valuable tool in the diagnosis of mucolipidoses and glycosphingolipidoses. Accurate resolution of the normal ranges of glycosidase activity is vital in the evaluation of both homozygotes and suspected heterozygote carriers. Activities of leukocyte β-galactosidase, α-galactosidase, α-mannosidase, β-fucosidase, β-glucosaminidase, and β-galactosaminidase were measured in a large population of normal subjects and demonstrated, within 95% confidence limits, to be normally distributed. Leukocyte glycosidases were determined in a GM1-gangliosidosis homozygote and in the heterozygous parents. A previously unreported deficiency of β-fucosidase and the well-known deficiency of β-galactosidase were demonstrated in the proband, and corresponding but less severe deficiencies of both glycosidases were found in the parents. β-Galactosidase and β-fucosidase may represent a single enzyme, unspecific for the carbon 6 of galactose. If not, the genetic defect in GM1-gangliosidosis may be more profound than has been recognized.