Clinical Application of Screening for GJB2 Mutations before Cochlear Implantation in a Heterogeneous Population with High Rate of Autosomal Recessive Nonsyndromic Hearing Loss

Heterogeneity of Hereditary Hearing Loss in Iran: a Comprehensive Review

A significant contribution to the causes of hereditary hearing impairment comes from genetic factors. More than 120 genes and 160 loci have been identified to be involved in hearing impairment. Given that consanguine populations are more vulnerable to most inherited diseases, such as hereditary hearing loss (HHL), the genetic picture of HHL among the Iranian population, which consists of at least eight ethnic subgroups with a high rate of intermarriage, is expected to be highly heterogeneous. Using an electronic literature review through various databases such as PubMed, MEDLINE, and Scopus, we review the current picture of HHL in Iran. In this review, we present more than 39 deafness genes reported to cause non-syndromic HHL in Iran, of which the most prevalent causative genes include GJB2, SLC26A4, MYO15A, and MYO7A. In addition, we highlight some of the more common genetic causes of syndromic HHL in Iran. These results are of importance for further investigation and elucidation of the molecular basis of HHL in Iran and also for developing a national diagnostic tool tailored to the Iranian context enabling early and efficient diagnosis of hereditary hearing impairment.

Frequency of Congenital Heart Diseases in Prelingual Sensory-Neural Deaf Children

INTRODUCTION

Hearing impairment is the most frequent sensorial congenital defect in newborns and has increased to 2-4 cases per 1,000 live births. Sensory-neural hearing loss (SNHL) accounts for more than 90% of all hearing loss. This disorder is associated with other congenital disorders such as renal, skeletal, ocular, and cardiac disorders. Given that congenital heart diseases are life-threatening, we decided to study the frequency of congenital heart diseases in children with congenital sensory-neural deafness.

MATERIALS AND METHODS

All children who had undergone cochlear implantation surgery due to SNHL and who had attended our hospital for speech therapy during 2008-2011 were evaluated by Doppler echocardiography.

RESULTS

Thirty-one children (15 boys and 16 girls) with a mean age of 55.70 months were examined, and underwent electrocardiography (ECG) and echocardiography. None of the children had any signs of heart problems in their medical records. Most of their heart examinations were normal, one patient had expiratory wheeze, four (12%) had mid-systolic click, and four (12%) had an intensified S1 sound. In echocardiography, 15 children (46%) had mitral valve prolapse (MVP) and two (6%) had minimal mitral regurgitation (MR). Mean ejection fraction (EF) was 69% and the mean fractional shortening (FS) was 38%.

CONCLUSION

This study indicates the need for echocardiography and heart examinations in children with SNHL.