Diagnosis of Krabbe disease by use of a natural substrate

This chapter describes in detail a practical procedure for the preparation of radiolabeled galactocerebroside and its use in the assay of galactocerebrosidase (GalCase), the enzyme deficient in globoid cell leukodystrophy (Krabbe disease). The reference range for leukocytes and fibroblasts is 0.9-4.4 and 8-36 nmoles substrate hydrolyzed per hour per milligram of protein, respectively. Because of its low abundance this enzyme is difficult to assay in certain situations, such as prenatal diagnosis by chorionic villus sampling. To obviate this a modified assay is used where only the radiolabeled substrate is included in the incubation. This provides a clear separation between affected samples and unaffected controls. The methods detailed here should be reproducible in any laboratory.