CTNS and nephropathic cystinosis: Nephropathic cystinosis is a rare, progressive, multisystemic lysosomal storage disorder occurring in approximately 1 in 100,000 to 200,000 live births.1, 2, 3 Cystinosis is caused by autosomal recessive inheritance of variants in the CTNS gene, which encodes for cystinosin, a lysosomal cystine transporter.2