Fig. 1.

Clinical characteristics of individuals with cystinosis.

(Top) Cystinosis patients lack a functional cystine transporter in the lysosomal membrane, so cystine remains inside the lysosome. Cysteamine converts cystine to cysteine and cysteine-cysteamine mixed disulfide, which freely exits the cystinotic lysosome via the lysine transporter. (Bottom) The biallelic mutations of the CTNS gene lead to elevated cystine levels in nearly all cells, resulting in renal damage corneal cystine crystals, myopathy, and rickets due to hypophosphatemia. (Figures used with permission of [[21], [25]]).