Quantified increases of cholesterol, total lipid and globotriaosylceramidein filipin-positive Niemann-Pick type C fibroblasts

Background: Niemann-Pick disease type C (NPC) is a neurovisceral lysosomal lipidosis caused in most cases by mutations in the NPC1 gene that codes for the cholesterol regulating NPC1 protein. Methods: Cultured skin fibroblast s from 11 NPC patients aged 0.25 to 34 years at diagnosis with different se verity of neurologic and visceral involvement, diagnosed by the cytochemica l filipin test for lysosomally stored cholesterol, were analyzed for lipid composition. Cholesterol and other lipids were separated on thin-layer chro matography from fibroblast total lipid extracts, quantified by densitometry and compared with the total cell lipid mass. Results: Cholesterol concentr ation in the patient cells was 1.5 to 5-fold higher than normal and total l ipids up to 2.4-fold normal. Cholesterol and total lipids were particularly high in cells from NPC patients aged less than about 6 years, and for-the whole patient series the abundance of fibroblast cholesterol was correlated with the tentatively assessed clinical disease severity. The findings in N PC suggested that NPC1 protein has a role not only in the balance of choles terol but also the distribution of the total cell lipid mass. Another incre ase found in the NPC cells was that of a minor lipid fraction, globotriaosy lceramide (Gb3, known as a cell signalling glycolipid). Gb3, in the average of its very variable individual concentrations, was about 2.5-fold higher in the NPC cell group as compared to normal or pathologic control group, bu t there was no correlation of Gb3 with the other lipid concentrations studi ed. Conclusions: For NPC diagnosis, the fibroblast cholesterol and total li pid quantification can be used as an alternative to the usual filipin test for lysosomal cholesterol, but both test methods are prone to equivocal res ults in cells from a small fraction of atypical NPC patients, where chemica l testing in organ biopsies or mutational analysis of the NPC1 gene should be tried. (C) 2001 Elsevier Science B.V. All rights reserved.