Unexpected heterogeneity due to recessive and de novo dominant mutations of GJB2 in an Iranian family with nonsyndromic hearing loss: Implication for genetic counseling

The mutation frequencies of GJB2, GJB3, SLC26A4 and MT-RNR1 of patients with severe to profound sensorineural hearing loss in northwest China

OBJECTIVE

To expose the spectrum and frequency of GJB2, GJB3, SLC26A4 and MT-RNR1 in northwest China and to investigate the underlying causative genes in patients without common mutations.

METHODS

We analyzed the mutation screening results of GJB2, GJB3, SLC26A4 and MT-RNR1 in 398 unrelated severe-to-profound probands with bilateral, symmetrical sensorineural hearing loss. Subsequently, we selected 10 probands with a significant family history of inherited hearing loss (HL) that did not have the above four common gene mutations to perform next-generation sequencing (NGS) of 139 known deafness genes, followed by co-segregation analysis of all available family members.

RESULTS

Among the 398 patients, 69 (17.34%) had the biallelic GJB2 gene mutations, and the most common mutations were c.235delC, c.109G>A and c.299_300delAT, with allele frequencies of 12.31%, 3.38% and 3.89%, respectively. A total of 63 (15.83%) cases with biallelic SLC26A4 mutations were detected, and the most common pathogenic alleles were c.919-2A>G, c.2168A>G and c.1174A>T, with allele frequencies of 9.17%, 2.26% and 0.88%, respectively. Mitochondrial gene mutations were detected in 9 (2.26%) patients, with 5 cases of mitochondrial DNA (mtDNA) m.1555A>G mutation and 4 cases of mtDNA m.1095T>C mutation. In 10 probands with a clear family history of HL, NGS showed two novel pathogenic variants in 2 families, including c.4129C>T/c.3268C>T in LOXHD1, c.334G>A/c.2968G>T in CDH23. Sanger sequencing confirmed that these variants segregated with the HL in each family.

CONCLUSIONS

Our results showed that GJB2 and SLC26A4 were the two major HL-causing genes in northwest China. The most common mutation alleles in GJB2 were c.235delC, c.109G>A and c.299_300delAT, and those in SLC26A4 were c.919-2A>G, c.2168A>G and c.1174A>T. In addition, both genes and their loci can be used as the first selection of deafness gene screening. Additionally, for patients who did not have mutations of these common genes, NGS provided an efficient diagnosis for increasing known deafness genes.

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.

Rare compound heterozygosity involving dominant and recessive mutations of GJB2 gene in an assortative mating hearing impaired Indian family

Connexin 26 (Cx-26), a gap junction protein coded by GJB2 gene, plays a very important role in recycling of potassium ions, one of the vital steps in the mechanotransduction process of hearing. Mutations in the GJB2 gene have been associated with both autosomal recessive as well as dominant nonsyndromic hearing loss. As Cx-26 is linked with skin homeostasis, mutations in this gene are sometimes associated with syndromic forms of hearing loss showing skin anomalies. We report here a non consanguineous assortatively mating hearing impaired family with one of the hearing impaired partners, their hearing impaired sibling and hearing impaired offspring showing compound heterozygosity in the GJB2 gene, involving a dominant mutation p.R184Q and two recessive mutations p.Q124X and c.IVS 1+1G>A in a unique triallelic combination. To the best of our knowledge, this is the first report from India on p.R184Q mutation in the GJB2 gene associated with rare compound heterozygosity showing nonsyndromic presentation.

Identification of a p.R143Q dominant mutation in the gap junction beta-2 gene in three Chinese patients with different hearing phenotypes

CONCLUSIONS

p.R143Q mutation in GJB2 can cause mild to profound bilateral sensorineural hearing impairment. Although not common in Chinese patients with hearing loss, it is important to identify the specific phenotype and genotype correlations of the dominant mutation in GJB2.

OBJECTIVE

Mutations in the GJB2 gene are the most common cause of nonsyndromic autosomal recessive sensorineural hearing loss. A few mutations in GJB2 have also been reported to cause dominant nonsyndromic or syndromic hearing loss. However, dominant mutation in GJB2 is not common in Chinese populations.

METHODS

Three patients with hearing impairment from Chinese families are reported here. Temporal CT scan, complete physical (including skin and hair) and otoscopic examinations, and an audiological study, including tympanometry, auditory brainstem response (ABR), auditory steady-state response (ASSR), and 40 Hz auditory event-related potential (40 Hz-AERP), were carried out. The two exons of GJB2, the coding exons of SLC26A4, and mitochondrial 12S rRNA were sequenced.

RESULTS

Sequencing of GJB2 in two patients showed a heterozygous c.428G>A (p.R143Q) mutation, and the third patient was identified with c.299delAT and c.428G>A compound heterozygous mutation. Sequence analysis of the coding exons of SLC26A4 and mitochondrial 12S rRNA was performed but no sequence aberration or deletion was found.

De novo dominant mutation of GJB2 in two Chinese families with nonsyndromic hearing loss

BACKGROUND

Mutations in the GJB2 gene are the most common cause of nonsyndromic autosomal recessive sensorineural hearing loss. A few mutations in GJB2 have also been reported to cause dominant nonsyndromic or syndromic hearing loss. However, de novo or dominant mutation in GJB2 is not common in Chinese populations.

METHODS

Two probands with hearing impairment from unrelated Chinese families are reported here. Temporal CT scan, complete physical (including skin and hair) and otoscopic examinations, and an audiological study, including tympanometry, auditory brainstem response (ABR), auditory steady-state response (ASSR), and 40Hz-auditory event-related potential (40 Hz-AERP), were carried out. The two exons of GJB2, the coding exons of SLC26A4, and mitochondrial 12S rRNA were sequenced.

RESULTS

Sequencing of GJB2 in the two cases showed a heterozygous c.551G>A(p.R184Q) mutation, which was not found in other family members. Additionally, no other mutation in GJB2 was identified in the two family members. Paternity was confirmed by genotype analysis of 15 informative short tandem repeats (STRs) from the chromosomes. Sequence analysis of the coding exons of SLC26A4 and mitochondrial 12S rRNA was performed but no sequence aberration or deletion was found.

CONCLUSIONS

A de novo GJB2 p.R184Q mutation can cause severe-to-profound bilateral sensorineural hearing impairment. Although not common in Chinese patients with hearing loss, it is important to identify the specific phenotype and genotype correlations of the de novo dominant mutation in GJB2.