Human cystinosis: intracellular deposition of cystine.

Membrane-limited inclusions were found in the cytoplasm of cells of the rectal mucosa, leukocytes, and cultured fibroblasts from two humans with cystinosis. Most of the inclusions contained amorphous material, presumably cystine. In cells of the rectal mucosa the material appeared frequently crystallized. This was rarely seen in leukocytes, and never in cultured fibroblasts. The fact that acid phosphatase could be demonstrated consistently in the organelles responsible for sequestration of cystine indicates that they are lysosomes.