High level of intrafamilial phenotypic variability of non-syndromic hearing loss in a Lur family due to delE120 mutation in GJB2 gene

Disease-associated variants of Gap Junction Beta 2 protein (GJB2) in the deaf population of Southern Punjab of Pakistan

Hearing impairment (HI) is a highly heterogeneous genetic disorder and is classified into nonsyndromic (without any other clinical manifestations) and syndromic (if combined with other clinical presentations) forms. Variations in GJB2 gene are the leading cause of autosomal recessive nonsyndromic hearing loss (ARNSHL) in several populations worldwide. This study was carried out to investigate the prevalence of GJB2 variations in severe-to-profound hearing impaired families of Southern Punjab of Pakistan. Ten families segregating ARNSHL were recruited from different areas of the region. Sanger sequencing of GJB2 coding region was carried out. In two out of ten families, NM_004004:c.*71G>A (p.(Trp24*)) and NM_004004:c.358_360del (p.(Glu120del)) homozygous variants were identified as the cause of hearing loss. Our study showed that GJB2-related hearing loss accounts for at least 20% of all cases with severe-to-profound hearing loss in the Southern Punjab population of Pakistan.

Investigation of the hearing levels of siblings affected by a single GJB2 variant: Possibility of genetic modifiers

OBJECTIVE

Variants in GJB2 can cause autosomal recessive deafness (DFNB1). There is evidence for genotype-phenotype correlations of GJB2 variants; however, several genotypes can cause varying levels of hearing loss likely attributable to differences in genetic or environmental background. As siblings share approximately 50% of their genetic background and usually have a common environmental background, analysis of phenotypes of siblings with a specific GJB2 variant may reveal factors relevant to phenotypic variation. There have been no previous analyses of differences in hearing among siblings carrying a single GJB2 genotype. Here, we investigated hearing differences between siblings with a single GJB2 variant, which can cause various levels of hearing loss.

METHODS

We examined hearing levels in 16 pairs of siblings homozygous for the c.235delC variant of GJB2. Differences in hearing acuity between sibling pairs were detected by auditory evaluation.

RESULTS

Average differences in acoustic threshold >30 dB were observed between five pairs of siblings, whereas the remaining 11 pairs had average threshold values within approximately 10 dB of one another. Hearing loss varied from moderate to profound.

CONCLUSION

Our results indicate that auditory acuity associated with homozygosity for GJB2 c.235delC can vary in degree; however, in approximately 70% of younger siblings, it was approximately the same as that in the first child, despite a diverse spectrum of hearing loss among different families. These results suggest that differences in genetic background may modify the phenotype associated with homozygous GJB2 c.235delC.

HBB mutations and HbA2 level: Escaping the carrier screening programs

HbA2 level alone for beta thalassemia trait may not be accurate and reliable even without iron deficiency so molecular genetic testing is important and should be considered for some individuals.

A novel pathogenic variant of SRD5A2 in an Iranian psuedohermaphrodite male

Deficiency of the 5‐alpha‐reductase may have an important role in 46,XY DSD in some cohorts. The prenatal ultrasonography and karyotyping can trigger the attention toward the presence of a DSD in fetus.

Role of GJB2 and GJB6 in Iranian Nonsyndromic Hearing Impairment: From Molecular Analysis to Literature Reviews

Background: Hearing impairment (HI) is a heterogeneous disorder. GJB2 and GJB6 genes are typically the first line of genetic screening before proceeding to any massive parallel sequencing. We evaluated the clinical utility of GJB2 and GJB6 testing in the Iranian population. Methods: GJB2 and GJB6 were sequenced. PubMed and Google Scholar were searched for Iranian publications on deletions in the DFNB1 locus. Results: We detected mutations of GJB2 in 16.5%, and no mutations of GJB6. Literature review revealed no reports of mutations of GJB6 in the Iranian population. Conclusion: This data and literature reviews indicate that GJB6 is not commonly responsible for Iranian nonsyndromic HI. Hence, the clinical utility of GJB6 genetic analysis as a first line for HI evaluation does not have the same utility as GJB2. The study is consistent with recent studies emphasizing the role of ethnicity in the selection of HI genetic testing strategy.

GJB2-related hearing loss in central Iran: Review of the spectrum and frequency of gene mutations

Mutations in the GJB2 gene are a main cause of autosomal-recessive nonsyndromic hearing loss (ARNSHL) in many populations. Previous studies have estimated the average frequency of GJB2 mutations to be ∼16% in Iran, but would vary among different ethnic groups. Here, we have taken together and reviewed results from our two previous publications and data from searching other published mutation reports to provide a comprehensive collection of data for GJB2 mutations and HL in central Iran. In all, 332 unrelated families were included and analyzed for the prevalence and type of the GJB2 gene mutations. In total, the frequency of GJB2 mutations was found to be 16% in the central provinces, which is significantly higher than those identified in southern populations of Iran. Also, c.35delG was the most frequent mutation in the related population. The present study suggests that mutations in the GJB2 gene, especially c.35delG, are important causes of HL in central Iran and can be used as a basis of genetic counseling and clinical guidelines in this region.

A novel PKP2 mutation and intrafamilial phenotypic variability in ARVC/D

Background: Arrhythmogenic ventricular cardiomyopathy (AVC) is an inherited cardiac disorder affecting 1 in 1000 individuals worldwide. The mean diagnosed age of disease is 31 years. In this article, an Iranian family reported that they were affected by ARVC due to a novel PKP2 mutation. Methods: Clinical evaluations, 12-lead ECG, CMR, and signal-averaged ECG were performed. After DNA extraction, genetic testing was done, and PCR-sequencing was applied to find causal mutations. Segregation analysis was also performed for the family. Results: ARVC criteria were documented in the patients. Genetic testing revealed a novel chain termination mutation (p.Tyr168Ter) in PKP2 gene; this mutation was transmitted from the mother to her 23-year-old son, but only the son was affected with ARVC. Conclusion: Modifier genes were indicated using interactome analysis of Plakophilin 2 protein (PKP2); they might have led to phenotypic variability through cellular mechanisms, such as nonsense-mediated mRNA decay. At least, 9 proteins were identified that might have affected Plakophilin 2 protein function, and consequently, rationalizing this intrafamilial phenotypic variability. This study highlighted the role of modifier genes involved in ARVC as well as the major role of PKP2 mutation in developing the disease in our population.

MYO15A splicing mutations in hearing loss: A review literature and report of a novel mutation

Sensorineural hearing loss (SNHL) is the most prevalent genetic sensory defect in humans, affecting about 1 in 1000 newborns around the world. Non-syndromic SNHL accounts for nearly 70% of hereditary hearing loss and 80% of SNHL cases show an autosomal recessive mode of inheritance (ARNSHL). In the present study, we applied targeted-exome sequencing to a family with a single proband affected by congenital sensorineural hearing loss. 127 known genes were sequenced to find the causative mutation. One novel homozygous donor splice site mutation, c.4596 + 1G > A (IVS12 + 1G > A) was found in MYO15A gene. Analysis of this mutation within the family showed that the mutation segregates with hearing loss. New DNA sequencing technologies could lead to identification of the disease causing variants especially in highly heterogeneous disorders such as hearing loss.

Screening of OTOF mutations in Iran: a novel mutation and review

OBJECTIVE

Mutations in OTOF have been reported to cause nonsyndromic hearing loss in different populations. The purpose of this study is screening of OTOF mutations in Iranian population.

METHODS

Thirty-eight consanguineous families affected with autosomal recessive nonsyndromic hearing loss (ARNSHL) and negative for GJB2 or GJB6 mutations were screened by autozygosity mapping and Sanger sequencing to find OTOF mutations.

RESULTS

A novel homozygous frameshift mutation (c.1981dupG) was found to cause hearing loss in one family and no other OTOF variants were detected in the remaining families. The affected individuals were homozygous forp. D661GfsX2 causing defect in long isoform of otoferlin.

CONCLUSIONS

We conclude that OTOF mutations are not the major cause of ARNSHL in the Iranian population but still may play an important role in HL; therefore evaluation the OTOF gene is of concern.