Gaucher disease types 1, 2, and 3: Differential mutations of the acid β-glucosidase active site identified with conduritol B epoxide derivatives and sphingosine

To elucidate the genetic heterogeneity in Gaucher disease, the residual β-glucosidase in cultured fibroblasts from affected patients with each of the major phenotypes was investigated in vitro and/or in viable cells by inhibitor studies using the covalent catalytic site inhibitors, conduritol B epoxide or its bromo derivative, and the reversible cationic inhibitor, sphingosine. These studies delineated three distinct groups (designated A, B, and C) of residual activities with characteristic responses to these inhibitors. Group A residual enzymes had normal I₅₀ values (i.e., the concentration of inhibitor that results in 50% inhibition) for the inhibitors and normal or nearly normal t( 1/2 ) values for conduritol B epoxide. All neuronopathic (types 2 and 3) and most non-Jewish nonneuronopathic (type 1) patients had group A residual activities and, thus, could not be distinguished by these inhibitor studies. Group B residual enzymes had about four- to fivefold increased I₅₀ values for the inhibitors and similarly increased t(2} values for conduritol B epoxide. All Ashkenazi Jewish type 1 and only two non-Jewish type 1 patients had group B residual activities. The differences in I₅₀ values between groups A and B also were confirmed by determining the uninhibited enzyme activity after culturing the cells in the presence of bromo-conduritol B epoxide. Group C residual activity had intermediate I₅₀ values for the inhibitors and represented a single Afrikaner type 1 patients: this patient was a genetic compound for the group A (type 2) and group B (type 1) mutations. These inhibition studies indicated that: (1) Gaucher disease type 1 is biochemically heterogeneous, (2) neuropathic and non-Jewish nonneuronopathic phenotypes cannot be reliably distinguished by these inhibitor studies, and (3) the Ashkenazi Jewish form of Gaucher disease type 1 results from a unique mutation in a specific active site domain of acid β-glucosidase that leads to a defective enzyme with a decreased V(max).