Somatic cell hybridisation studies showing different gene mutations in Niemann-Pick variants.

Cultured skin fibroblasts from patients with different clinical types of Niemann-Pick disease were hybridized and sphingomyelinase activities were measured in the heterokaryon cell population. Both the natural substrate (3H-choline) sphingomyelin and the chromogenic analogue hexadecanoylamino-4-nitrophenylphosphorylcholine were used in the complementation analysis. In fusions between cells from type C Niemann-Pick disease with those from type A or B a clear restoration of sphingomyelinase activity occurred, whereas no complementation was found in other fusion combinations. The results indicate that at least two different genes are involved in the mutations leading to the different Niemann-Pick variants.