Study of MYOC Gene Mutation in POAG Patients in Zahedan, Iran.

BACKGROUND: The second cause of blindness in the world is glaucoma that begins with visual impairments and, in many cases, ends with irreversible visual loss. Primary open-angle glaucoma (POAG) is the most common type of glaucoma, which causes irreversible optic nerve damage in adults. Glaucoma shows an unknown etiology, but there is strong evidence regarding the role of genetic factors in disease establishment. For determination of the role of MYOC gene mutations in the development of POAG in Zahedan, Iran, screening of this gene was performed. METHODS: Forty-five POAG patients were recruited from Noor Pajoohan Shargh clinic and Al-Zahra Eye Hospital, Zahedan University of Medical Sciences, Zahedan, Iran. Three exons of the MYOC gene were amplified in five amplicons, using polymerase chain reaction (PCR). Then PCR products were sequenced using the ABI big dye ABI Prism 3700 instrument in forward and reverse directions with the same primers. RESULTS: Five variations were found in POAG patients: two known variations (rs2075648 and rs2234926) in exon 1, one in exon 2 (rs58117216), and two variants (rs74315330 and rs146606638) in exon 3. They were not all associated with the disease status and are known as normal variants. However, there was a mutation in exon 3 (Gln297 His or CM081349) only in one patient which is known as the disease causing mutation in some populations [1]. CONCLUSIONS: Since most of POAG patients had no mutation in the MYOC gene, other genes might have been involved in the pathogenesis of the disease.

Genotyping results of Iranian PCG families suggests one or more PCG locus other than GCL3A, GCL3B, and GCL3C exist.

PURPOSE: To assess whether loci other than GLC3A, GLC3B, and GLC3C are linked to primary congenital glaucoma (PCG). METHODS: The gene CYP1B1 at GLC3A was screened in 19 Iranian PCG probands who had been recruited mostly from among individuals of Turkish ethnicity and individuals from central and eastern Iran. The gene MYOC was screened in patients from this cohort who lacked CYP1B1 mutations and in ten patients previously shown not to carry CYP1B1 mutations. Family members of 19 probands without mutations in either of these genes were recruited for assessment of linkage to GLC3B and GLC3C by genotyping microsatellite markers. In total, 127 individuals, including 35 affected with PCG, were genotyped. RESULTS: Eleven (57.9%) of the newly recruited PCG patients did not carry disease-associated mutations in CYP1B1. Disease-associated MYOC mutations were not observed in any of the patients screened. Inheritance of PCG in all the families was consistent with an autosomal recessive pattern. Linkage to GLC3B and GLC3C was ruled out in nine of the families on the basis of autozygosity mapping and haplotype analysis. CONCLUSIONS: Observation of the absence of linkage to GLC3B and GLC3C in at least nine families without CYP1B1 mutations suggests that at least one PCG-causing locus other than GLC3A, GLC3B, and GLC3C may exist. The disease-causing gene or genes in the novel locus or loci may account for PCG in a notable fraction of Iranian patients.

CYP1B1 mutation profile of Iranian primary congenital glaucoma patients and associated haplotypes.

The mutation spectrum of CYP1B1 among 104 primary congenital glaucoma patients of the genetically heterogeneous Iranian population was investigated by sequencing. We also determined intragenic single nucleotide polymorphism (SNP) haplotypes associated with the mutations and compared these with haplotypes of other populations. Finally, the frequency distribution of the haplotypes was compared among primary congenital glaucoma patients with and without CYP1B1 mutations and normal controls. Genotype classification of six high-frequency SNPs was performed using the PHASE 2.0 software. CYP1B1 mutations in the Iranian patients were very heterogeneous. Nineteen nonconservative mutations associated with disease, and 10 variations not associated with disease were identified. Ten mutations and three variations not associated with disease were novel. The 13 novel variations make a notable contribution to the approximately 70 known variations in the gene. CYP1B1 mutations were identified in 70% of the patients. The four most common mutations were G61E, R368H, R390H, and R469W, which together constituted 76.2% of the CYP1B1 mutated alleles found. Six unique core SNP haplotypes were identified, four of which were common to the patients with and without CYP1B1 mutations and controls studied. Three SNP blocks determined the haplotypes. Comparison of haplotypes with those of other populations suggests a common origin for many of the mutations.