Screening of CHST6 for mutations in Iranian macular corneal dystrophy patients

Macular corneal dystrophy (MCD; OMIM 217800) is a rare autosomal recessive inherited ocular disorder that manifests with progressive and bilateral development of punctuate gray-white opacities underneath the epithelium of the cornea, in the stroma, Descemet’s membrane and endothelium. Based on immunohistochemical studies MCD is subdivided into three types (I, IA and II); these types are clinically indistinguishable. In 2000, mutations in CHST6 gene (OMIM 605294) were identified as cause of MCD. Until now, numerous missense mutations and some nonsense mutations, insertions, deletions within the coding region and rearrangement in the upstream region of CHST6 have been identified in MCD patients. CHST6 encodes a sulfotransferase enzyme that transfers sulfate to unsulfated keratan chains. Deficiencies in the CHST6 enzyme observed in MCD patients result in deposition of poorly sulfated or non-sulfated keratin sulfate in the intracellular and extracellular matrix of the cornea. The clinical consequence of these deposits is corneal opacity and loss of vision. The aim of this study is to screen CHST6 mutations in Iranian MCD patients.Methods: Ten MCD affected patients diagnosed by a cornea specialist (A.B) were recruited. DNA was extracted and protein coding exon of CHST6 gene was amplified by the polymerase chain reaction (PCR). Subsequently, PCR products were sequenced with the Sanger protocol.Results: Nine out of ten patients had homozygous missense mutations in CHST6, eight of which had already been found in MCD patients and one of which was novel (c.262C> G which results in p.Leu88Val). No mutation was detected in one patient.Conclusion: As in other populations studied, mutations in CHST6 appear to be the major cause of MCD in Iranian patients. As a mutation was not observed in the coding exon of one of the patients, In addition to screening of protein coding sequences and as rearrangements in the upstream region of CHST6 have been reported, it is appropriate to screen this region of the gene in some patients.