Ctns, encoding the lysosomal membrane protein cystinosin, is crucial as it transports cystine out of lysosomes into the cytoplasm [1,2,3,4]. Mutations in Ctns lead to cystinosis, an autosomal recessive lysosomal storage disorder [1,2,3,4]. The associated disruption in cystine transport results in intra-lysosomal cystine accumulation in all body cells and organs, with the kidneys often being initially affected [2].

Cystinosis has different forms related to Ctns mutations. Nephropathic or infantile type, the most common, is characterized by renal failure at around 10 years of age and other systemic complications, associated with 32 different Ctns mutations [1]. Intermediate cystinosis, with later-onset renal disease, is linked to three different mutations, and benign or non-nephropathic cystinosis, presenting with corneal crystals and photophobia, is associated with two other mutations [1]. In general, only certain splicing or missense mutations are related to milder phenotypes [1]. More than 140 Ctns mutations have been reported worldwide [3]. Different studies have identified various mutations in different populations. For example, in Iranian nephropathic cystinosis patients, mutations were found in exons 6 and 7 in 50% of cases, and novel mutations were also detected [5]. In Tunisian patients with ocular cystinosis, 7 mutations were disclosed, including missense, duplication, frameshift, and splice-site mutations [6].

In conclusion, Ctns is essential for normal cystine transport from lysosomes. Studies on Ctns-related cystinosis, through identification of various mutations in different populations, help understand the molecular basis of the disease. This knowledge is fundamental for developing new therapeutic strategies, such as targeted gene therapy, to address the kidney and extra-renal phenotypes of cystinosis [3].