COMPLEMENTATION STUDIES IN NIEMANN-PICK DISEASE TYPE-C INDICATE THE EXISTENCE OF A 2ND GROUP

Niemann-Pick disease type C is a clinically heterogeneous storage diso rder with an unknown primary metabolic defect. We have undertaken soma tic cell hybridisation experiments using skin fibroblast strains from 12 patients representing a wide clinical spectrum. Preliminary experim ents using filipin staining of free cholesterol as a marker for comple mentation indicated the existence of one major group (group alpha) and one minor group (group beta) represented by one mutant strain. Subseq uent experiments in which sphingomyelinase activity was measured as a marker for complementation using five mutant strains showing activity consistently <40% control levels confirmed the existence of the second group.