CTNS and cystinosis: Cystinosis (OMIM 219800), the most common cause of renal Fanconi syndrome, is a lysosomal transport disorder with an autosomal recessive inheritance pattern, resulting from different mutations in the CTNS gene that is located on chromosome 17p13.1,2 The CTNS gene contains 12 exons with a coding region of 1,104 bp.3 The last 10 exons encode a lysosomal transmembrane protein with 367 amino acids called cystinosin.