Epidemiology, etiology, genetic variants in non- syndromic hearing loss in Iran: A systematic review and...

Hearing loss is one of the most common heterogeneous complicated disorders worldwide. We previously analyzed the results of published data on non-syndromic hearing loss in the Iranian population systematically. A broad range of genes is a challenge for molecular screening and clinical diagnosis in our populations on the ground of distinct genetics. The aim of this study was to analyze the role and frequency of the variants accountable for non-syndromic hearing loss (NSHL) in the Iranian population. These were identified with different methods including whole exome sequencing (WES), next-generation sequencing (NGS), targeted genomic enrichment and massively parallel sequencing (TGE + MPS), autozygosity mapping, STR markers, linkage analysis, and direct sequencing. This is the comprehensively study focusing on classifying 13 common NSHL genes according to their frequencies. Previous studies have not studied different regions and the Iranian population, and this is the definitive study on the topic.

We searched Scopus, PubMed, Science Direct databases, and Google Scholar. After a systematic review of the evidence 95 studies were considered then 31 studies were eligible for meta-analysis. In total, 6995 families, 358 variants, and 117 novel variants were included. Statistical analyses were conducted using Stata SE version 11 software. The inverse variance method enjoyed combining data. Heterogeneity of the preliminary results was assessed using Q (Cochrane test), and I square index. Random effects or fixed models were applied to combine the results, relying on the degree of heterogeneity. Point and pooled prevalence of variants acting on different regions were illustrated by forest plots.

The total prevalence of at least one variant of GJB2 and SLC26A genes was estimated at 26% and 5%, respectively. Variant c.35delG accounted for 18% of the GJB2 variants while 1% of these variants were novel ones. The next most common variants in the GJB2 gene were c.109G>A at 3.5% and c.-23+1G>A at 2.3%. Moreover, the prevalence of GJB2 gene variants varied on average 0.002% from one region to another in Iran (p=0.849). Our meta-analysis also showed that the frequency of at least one variant of MYO15A varied between 1.2% and 12.5%. Corresponding prevalences for the other variants were as follows: ILDR1 (3.5%-3.7%), CDH23 (2%-10%), PJVK (1.4%-33%), TECTA (1.3%-6.7%), MYO6 (2%-4.8%), TMC1 (1.8%-2%), MYO7A (0.7%-5%), MARVELD2 (0.7-5%), OTOF (0.7%-4%), LRTOMT (0.7%-2.5%). Finally, we did not find any relationship between geographic area and the presence of these variants.

GJB2 gene variants were the most common cause of NSHL in Iran. Understanding the prevalence of NSHL gene frequency in Iran may be the foundation for future studies in an Iranian population which may lead to future NSHL therapy.