Frequencies of Six (Five Novel) STR Markers Linked to TUSC3 (MRT7) or NSUN2 (MRT5) Genes Used for Homozygosity Mapping of Recessive Intellectual Disability.

BACKGROUND: Non-syndromic autosomal recessive intellectual disability (NS-ARID) is an extremely heterogeneous genetic disorder. Therefore, to investigate these genes, more research is required. One approach to investigate the NS-ARID loci is homozygosity mapping which requires appropriate STR markers within or flanking the gene/s of interest. In this research, we aimed to find novel STRs for two common NS-ARID genes (TUSC3 and NSUN2) and, in addition, to identify allele frequencies of those STR markers. METHODS: The study group included 119 unrelated healthy individuals. STR markers were investigated using the UCSC genome browser web site and SERV software. Genotyping was determined by multiplex PCR. Data were evaluated using Gene Mapper software. Allele frequencies and observed heterozygosity rates were calculated using PowerStatV12. Deviation from Hardy-Weinberg equilibrium and expected heterozygosity were assessed using the DNAView software. RESULTS: In total, 56 alleles were detected. According to our research, D8TUSC3SU8.3 and D5NSUN2SU0.5 were the most informative STR markers in MRT7 and MRT5 loci, respectively and showed a high percentage of heterozygosity in Iranian population. The observed range of allele frequencies was from 3.4% to 32.4% and 0.8% to 18.9% for MRT5 and MRT7 loci, respectively. Further, we have evaluated other statistical surveys of these STR markers and discovered that all of the six listed STRs were informative and five meet the Hardy-Weinberg equilibrium for the tester group. CONCLUSIONS: Finding novel STRs, with high allele heterozygosity, is one of the most significant current finding in the present study for the two common NSARID genes. The recognized heterozygosity of these markers make MRT flanking STR markers very efficient to be used in diagnostic medical genetics labs or homozygosity mapping on NS-ARID.

GJB2 c.-23+1G>A mutation is second most common mutation among Iranian individuals with autosomal recessive hearing loss.

GJB2 mutation analysis is used routinely as a first step in genetic testing for autosomal recessive non-syndromic sensorineural hearing loss. Although most GJB2 mutations can be detected by sequencing of the exon 2 of this gene, a prevalent splice mutation, c.-23+1G>A (IVS1+1G>A), is not usually included in the analyzed region. In this study, we have developed an ARMS-PCR strategy for detection of this mutation among Iranian deaf individuals. A total of 418 Iranian individuals with hearing loss consistent with autosomal recessive non-syndromic sensorineural hearing loss based on audiological test result, medical history, physical examination and pedigree of the family, were included in this study. c.35delG and c.-23+1G>A mutations were detected by using ARMS-PCR. Direct sequencing of the exon 2 of the GJB2 gene was performed for mutation analysis of the coding region of this gene. Among 418 investigated cases, a total of 81 patients (~19.4 %) with biallelic pathogenic mutations in the GJB2 gene and 13 cases with only one pathogenic mutant allele were identified. The total allele frequencies of the two most frequent mutations, c.35delG and c.-23+1G>A, among mutated alleles were found to be around 59 and 15.7 %, respectively. High frequency of the c.35delG and c.-23+1G>A mutations among Iranian deaf individuals shows the importance of developing rapid and cost-effective methods for primary mutation screening methods before performing direct sequencing.

Identification of a novel mutation in congenital afibrinogenemia in Iranian patients.

Congenital afibrinogenemia is a rare autosomal recessive disorder that is caused by defects in the fibrinogen. Fibrinogen is a hexameric glycoprotein made of two pairs of three homologous polypeptide chains including Aα, Bß, and γ that are encoded by three genes named FGA, FGB, and FGG. We aim to study four Iranian families who were referred to our lab for molecular diagnosis of afibrinogenemia. Genomic DNA was extracted from whole blood and Sanger sequencing was performed using primers for all exons and exon-intron junctions of FGA, FGB, and FGG genes. Pathogenicity of the variants was predicted using different in-silico tools and was interpreted according to the American College of Medical Genetics and Genomics guideline. We found three types of mutations in the studied families; two were in the FGA gene and one was in the FGB gene including a nonsense, a novel splicing mutation, and two deletion ones. The nonsense and the deletion mutations may cause a truncated protein and are likely pathogenic and pathogenic, respectively. The novel mutation of splicing found in the FGB gene is a pathogenic one and can break the wild-type acceptor site. Studying mutations in afibrinogenemia patients can expand our knowledge about this disease in Iran.