Assay of ß-Glucosidase and Sphingomyelinase for Identification of Patients and Carriers of Gaucher’s and Niemann-Pick Diseases

Abstract

Since the middle 1960’s the enzymatic defects in Gaucher and Niemann-Pick diseases have been recognized (1,2). Both autosomal recessive diseases are caused by a deficiency of a lysosomal enzyme required for the degradation of normal cell components. Gaucher disease presents clinically in at least three sub-types: adult form (non-neuropathic or Type 1), infantile form (acute neuropathic or Type 2) and juvenile form (subacute neuropathic or Type 3). Although the patients are quite different in clinical picture all appear to have a deficiency of glucosylceramide ß-glucosidase activity in all tissues tested. Early studies on easily obtained tissues such as leukocytes and cultured skin fibroblasts demonstrated that diagnosis of affected patients was possible without the need for organ biopsy (3). Although much of the earliest research on the enzyme defect was done using radioactively labeled glucosylceramide, additional studies demonstrated that the synthetic ß-glucoside, 4-methylumbelliferyl-ß-D-glucoside,could be used for diagnosis and identification of carriers in easily obtained tissue samples (4,5). Through a measurement of the ability of a tissue sample to hydrolyze this synthetic derivative, a measure of the ability to hydrolyze the natural substrate should be interpreted. Although these methods are workable in some laboratories frequently problems arose in the interpretation of the values. Due to the limited number of laboratories having the natural substrate suitably labeled, it would be preferable to use the commercially available synthetic substrate, if a reliable method were developed. It is known that bile salt detergents are required in the in vitro assay for hydrolysis of some natural sphingolipids.