The diagnosis of cystinosis in patients reveals new CTNS gene mutations in the Chinese population.

Background Cystinosis is a rare autosomal-recessive disorder caused by a defective transport of cystine across the lysosomal membrane. Previous studies have mapped cystinosis to the CTNS gene which is located on chromosome 17p13, and various CTNS mutations have been identified to correlate them with this disease. Methods We analyzed six patients from five unrelated families who were diagnosed with cystinosis in our hospital. We described the diagnostic procedures for all the patients and proposed alternative therapies for cystinosis patients instead of using cysteamine, an orphan drug which was commercially unavailable in China. Moreover, genetic analysis of all patients' samples was carried out to identify novel CTNS gene mutations. Results and conclusions The patients in this study were followed up from 1 to more than 10 years to monitor their growth and development, which indicated that the alternative therapies we used were helpful to ameliorate the complications of the cystinosis patients without cysteamine. Furthermore, by sequencing the patients' genome, we identified novel mutations in the CTNS gene including: c.477C > G (p.S159R), c.274C > T (p.Q92X) and c.680A > T (p.E227V); these mutations were only observed in cystinosis patients and had never been reported in any other populations, suggesting they might be specific to Chinese cystinosis patients.