Major conceptual break-throughs include (a) its discovery in 1903, (b) recognition of the renal Fanconi syndrome, (c) realization that tissue accumulation of cystine reflects a defective channel in the lysosomal membrane, (d) translation of this discovery to trials of cysteamine, (e) discovery of the CTNS gene, and (f) report of successful stem cell therapy in the cystinotic mouse. The gene discussed is CTNS; the disease is Fanconi renotubular syndrome.