Biochemical diagnosis of cystinosis using cultured cells.

A simple method is described for the biochemical diagnosis of cystinosis using small numbers of cells cultured in medium containing l-S-cystine. Nonprotein sulphur-labelled compounds were extracted from the cells and separated by thin-layer chromatography. The abnormally high incorporation of S-cystine by cystinotic skin fibroblasts was apparent on visual examination of autoradiographs of the chromatograms and was quantitated by comparison with the incorporation of S into glutathione. The method was used to confirm the diagnosis of 6 cystinotic patients. The incorporation of S-cystine by 2- to 3-week cultures of control amniotic fluid cells obtained in early pregnancy was similar to that of control skin fibroblasts, suggesting that the method would also be of use in the early prenatal detection of cystinosis.