CTNS encodes cystinosin, a lysosomal membrane cystine/H+ symporter that mediates the export of cystine from lysosomes into the cytoplasm 1. Beyond cystine transport, cystinosin plays important roles in melanin synthesis by catalyzing cystine export from melanosomes 2 and acts as a positive regulator of mTORC1 signaling in kidney proximal tubular cells through interactions with v-ATPase and Ragulator complexes 3. Mutations in CTNS cause cystinosis, an autosomal recessive lysosomal storage disorder characterized by intra-lysosomal cystine accumulation in all body cells 1. Over 140 CTNS mutations have been identified worldwide, with clinical severity correlating with mutation type 3. The nephropathic form, most common in infants, causes renal Fanconi syndrome within the first year of life, progressing to end-stage renal failure by mid-childhood without treatment, alongside multi-organ involvement including eyes, thyroid, pancreas, and CNS 1. Intermediate and non-nephropathic forms present with later-onset renal disease or corneal symptoms only 4. Early and sustained cysteamine therapy has dramatically improved outcomes, extending life expectancy into adulthood 5. Recent research reveals cystinosin also regulates oxidative state, lysosomal dynamics, and autophagy, suggesting potential for gene therapy approaches 3.