CTNS Mutations Causing Autosomal Recessive Cystinosis in a Subset of Iranian Population: Report of Two New Variants

Abstract

Background: Nephropathic cystinosis (NC) is an uncommon autosomal recessive disease with abnormality in lysosomal storage that appearances in patients with mutations in the CTNS gene encoding a lysosomal transporter cystinosin. Disrupted function of this transporter is followed by accumulation of cysteine crystals in cells of many various organs. This study aimed to investigate the mutations of the CTNS gene in 20 Iranian patients suffering from NC.

Materials and methods: Twenty Iranian cystinosis patients referring to Imam Hossein Hospital of Isfahan were employed in this case-series study. After extraction of genomic DNA, the promoter and entire coding regions of CTNS were analysed using sanger sequencing in all patients. Gap-Polymerase Chain Reaction was used to detect 57 kb deletion in the CTNS gene. In silico study was performed to analyse variants.

Results: The large deletion was not seen in any NC patients. Molecular analysis which conducted to screen the CTNS gene of patients, identified eight different mutations, including two new mutations, c.971_972insC and c.956_956delA, which have not been reported before, and c.681G>A mutation, which was identified as a frequently founded mutation in the Middle East and was observed in 35% of patients. In this study, five other mutations including c.1015G>A, c.922G>A, c.323_323delA, c.433C>T, and c.18_21delGACT were also observed, which have been reported in previous studies.

Conclusion: The mutational spectrum in the Iranian patients is the same as previously reported mutations except that two new mutations were found. The present findings will present suggestions for regular molecular diagnosis of cystinosis in Iran.

Keywords: Genetic variations; lysosomal storage disease; molecular diagnostic testing; nephropathic cystinosis.

Figure 1

Localization of identified mutations in the study. (a) Four detected mutations are related to exons 3, 6, 7, and 9; while two mutations are occurred in exon 11, and two of them are in exon 12 (b) CTNS is a seven-passed transmembrane receptor and we have detected two new mutations affecting residues 319 and 325 in the protein

Figure 2

Data of two new mutations. (a) NCBI blast (b) Chromatogram (Chromas software version 2.6.6) for the region containing two novel mutations. The substituted nucleotides are shown by red arrow shows. (a) illustrates a single base pair deletion in nucleic acid position 956 (c.956_956delA) in exon 11, resulting in formation of truncated protein (Q319Rfs*10) which was detected in two patients in homozygous condition. (b) shows an insertion in exon 12 (c.971_972insC) in one family, leading to truncated protein (Q325Pfs*40). (c) Family pedigree of patients