THE GLUCOCEREBROSIDASE D409H MUTATION IN GAUCHER-DISEASE

Gaucher disease, resulting from the decreased activity of the lysosoma l enzyme glucocerebrosidase, is the most prevalent sphingolipid storag e disease. Due to considerable heterogeneity of phenotypic expression, it has been subdivided into the nonneurological type 1 disease, and t ypes 2 and 3, the neurological types. We describe homozygosity for the D409H mutation within the glucocerebrosidase gene associated with a u nique form of type 3 Gaucher disease. Twelve patients, originating fro m three Arab sibships, were found to be homozygous for the D409H mutat ion. They all presented with oculomotor apraxia and a progressive card iac valve defect with minimal organomegaly. When expressed in human ce lls in tissue culture, using the T7/EMC/vaccinia virus hybrid expressi on system, we were able to demonstrate that the mRNA carrying the D409 H mutation was less stable than the normal counterpart. Pulse-chase ex periments demonstrated that the mutated protein exhibited lower stabil ity than the normal counterpart. Its activity toward the artificial su bstrate 4-methyl umbelliferyl glucopyranoside was similar to that of t he mutated enzymes carrying the N370S or the L444P mutations. However, in loading experiments using lissamine-rhodamine conjugated glucosyl ceramide as a substrate, the recombinant mutated protein carrying the D409H mutation exhibited 28.63 +/- 6.05% of the activity exhibited by the normal enzyme. L444P and N370S mutations exhibited 51.90 +/- 7.16 and 115.75 +/- 12.64% of normal enzyme activity, respectively. Loading of cells homozygous for the D409H mutation demonstrated 10.05% of the activity shown by normal cells. L444P and N370S homozygous cells demo nstrated 25.3 and 98.5% of foreskin fibroblast glucocerebrosidase acti vity, respectively. We demonstrate that homozygosity for the D409H mut ation is a unique case of a peculiar phenotype associated with a speci fic intracellular glucocerebrosidase activity. (C) 1996 Academic Press , Inc.