CTNS and cystinosis: Renal Fanconi syndrome, the most common inherited form of cystinosis in children 65, 68, 69, is caused by mutations in the CTNS gene, which encodes for cystinosin, a proton symporter that transports cystine out of the lysosomal compartment with proton-electromotive force generated by vacuolar (H+)-ATPase 64, 70, 71.