Glucosylceramide accumulation is not confined to the lysosome in fibroblasts from patients with Gaucher disease.

Gaucher disease (GD) is an inborn error of glycosphingolipid metabolism resulting from a deficiency of the lysosomal enzyme beta-glucosidase leading to the accumulation of glucosylceramide (GC) in lysosomes of affected cells. In order to determine the effect of GC accumulation on intracellular lipid content in fibroblasts from patients with GD, we measured individual species of ceramide, di- and trihexosylceramide, sphingomyelin, phosphatidylcholine, phosphatidylinositol and phosphatidylglycerol using electrospray ionisation-tandem mass spectrometry. The different subspecies of each lipid class correlated with each other and were summed to give total lipid concentrations. In addition to GC, we also noted secondary elevations in other lipids, especially in type 2 GD. Sub-cellular fractionation showed that GC was not confined to the lysosome but increased throughout the cell. The sequelae of extra-lysosomal accumulation may have implications in the pathogenic mechanisms of GD by interaction with biochemical and metabolic pathways located outside the lysosome. The elevation of ceramide in confluent type 2 GD fibroblasts redistributed from its primary site of accumulation in the lysosome to the endosomal region at four-weeks post-confluence. The accumulation of lipids in the endosome and lysosome suggests both impaired trafficking of lipids and reduced capacity of the lysosome to degrade lipids.

Immunoquantification of alpha-galactosidase: evaluation for the diagnosis of Fabry disease.

BACKGROUND: Fabry disease is an X-linked inborn error of glycosphingolipid catabolism resulting from a deficiency of the lysosomal exoglycohydrolase, alpha-galactosidase. Enzyme replacement therapy is currently available for Fabry disease, but early diagnosis before the onset of irreversible pathology will be mandatory for successful treatment. Presymptomatic detection would be possible through the use of a newborn-screening program. We report on the use of sensitive assays for the measurement of alpha-galactosidase protein and activity and for the protein saposin C, which are diagnostic markers for Fabry disease. METHODS: Two sensitive immunoassays for the measurement of alpha-galactosidase activity and protein were used to determine the concentrations of alpha-galactosidase in dried filter-paper blood spots and plasma samples from control patients and patients with a lysosomal storage disorder (LSD). RESULTS: Fabry hemizygous individuals were clearly identified from control populations by decreases in both alpha-galactosidase activity and protein. Fabry heterozygotes generally fell between the hemizygotes and controls. Including the measurement of saposin C enabled differentiation between Fabry heterozygotes and controls. In blood spots, all Fabry individuals could be distinguished from control blood spots as well as from 16 other LSD patients. CONCLUSIONS: The determination of alpha-galactosidase activity or protein in dried filter-paper blood spots could be used for the diagnosis of Fabry patients. With further validation, these assays could be used for the identification of Fabry patients in newborn-screening programs and may also be suitable for screening high-risk populations.