An Indian boy with nephropathic cystinosis: a case report and molecular analysis of CTNS mutation

Cystinosis is a rare autosomal recessive lysosomal storage disorder characterized by excessive accumulation of cystine within the lysosome. Cystinosis is caused by mutations in the lysosomal cystine transporter, cystinosin (CTNS). The CTNS gene consists of 12 exons and encodes for an integral lysosomal membrane protein with seven transmembrane domains. A majority of cystinotic patients are of European descents, and only a few cases have been reported from other ethnic groups. Here we report a case of nephropathic cystinosis in an Indian boy born to consanguineous parents. Major symptoms of the patient include weight loss, vomiting, dehydration, and cystine crystals in the cornea. Ichthyosis on the arms and legs is also observed. Sequencing analysis of all the CTNS exons revealed that the proband is homozygous for a 3-bp in-frame deletion in exon 10 (c.809_811delCCT), resulting in the loss of a conserved p.Ser270del within the fifth transmembrane domain of CTNS. His parents are both heterozygous for the same mutation. This work represents the first molecular characterization of cystinotic patients from India. Interestingly, a p.Ser270del resulting from c.809_811delCCT in CTNS had been identified in a European patient. Therefore, it appears that this mutation arose independently in the two different continents.