Hearing loss associated with an unusual mutation combination in the gap junction beta 2 (GJB2) gene in a Chinese family

A novel method for detecting nine hotspot mutations of deafness genes in one tube

Deafness is a common sensory disorder. In China, approximately 70% of hereditary deafness originates from four common deafness-causing genes: GJB2, SLC26A4, GJB3, and MT-RNR1. A single-tube rapid detection method based on 2D-PCR technology was established for nine mutation sites in the aforementioned genes, and Sanger sequencing was used to verify its reliability and accuracy. The frequency of hotspot mutations in deafness genes was analysed in 116 deaf students. 2D-PCR identified 27 genotypes of nine loci according to the melting curve of the FAM, HEX, and Alexa568 fluorescence channels. Of the 116 deaf patients, 12.9% (15/116) carried SLC26A4 mutations, including c.919-2A > G and c.2168A > G (allele frequencies, 7.3% and 2.2%, respectively). The positivity rate (29.3%; 34/116) was highest for GJB2 (allele frequency, 15.9% for c.235delC, 6.0% for c.299_300delAT, and 2.6% for c.176-191del16). Sanger sequencing confirmed the consistency of results between the detection methods based on 2D-PCR and DNA sequencing. Common pathogenic mutations in patients with non-syndromic deafness in Changzhou were concentrated in GJB2 (c.235delC, c.299_300delAT, and c.176-191del16) and SLC26A4 (c.919-2A > G and c.2168 A > G). 2D-PCR is an effective method for accurately and rapidly identifying deafness-related genotypes using a single-tube reaction, and is superior to DNA sequencing, which has a high cost and long cycle.

Undescribed GJB2 c.35dupG homozygous prelingual distinguished from c.35delG homozygous/compound heterozygous deafs, dwelling a German ancestry Venezuelan isolate

Background

Among ten hearing-impaired (HI) families mostly of German descent dwelling the Venezuelan isolate Colonia Tovar, which were initially studied several decades ago to assess the etiology of their profound/prelingual nonsyndromic deafness phenotype, an undescribed genotype/phenotype was found. Forty-eight subjects, including 8 of the still living 143 originally searched with audiograms 4 decades ago, were retested and their DNA collected. A genomic search of 27 loci involved in HI was performed on a randomly chosen prelingual deaf patient. Subsequently, GJB2 sequencing was performed in all subjects from each pedigree. Haplotypes were constructed with five intragenic GJB2 SNPs (rs117685390, rs7994748, rs2274084, rs2274083, and rs3751385). Audiograms performed along 5 decades were compared to evaluate age-related hearing loss in the different genotypes found in the population.

Results

Three prelingual deaf siblings, having the highest recorded symmetrical hearing loss of all the known affected in the isolate, carried the very rare mutation c.35dupG (p.V13Cfs*35) at GJB2 in a homozygous condition. Two additional GJB2 mutations were identified (p.W77R and c.35delG) in the isolate. Allelic disequilibrium in both c.35dupG and p.W77R carriers (with in-phase haplotype T;T;G;A;C) were found, although not so in the 2 other found c.35delG independent haplotypes. A compound heterozygote in trans (c.35delG/c.35dupG) was audiometrically distinguishable from both the c.35dupG and c.35delG homozygotes.

Conclusions

A relatively higher frequency of mutation of c.35dupG found than elsewhere was retrospectively inferred for the ancient population of the Kaiserstuhl region in Germany, having an opposite epidemiological situation to the one found with the contiguous and very frequent c.35delG. Haplotype analysis suggests founder phenomena and independent occurrence, hundreds of generations back in Caucasoid populations for both mutations.

Diverse pattern of gap junction beta-2 and gap junction beta-4 genes mutations and lack of contribution of DFNB21, DFNB24, DFNB29, and DFNB42 loci in autosomal recessive nonsyndromic hearing loss patients in Hormozgan, Iran

BACKGROUND

We aimed to determine the contribution of four DFNB loci and mutation analysis of gap junction beta-2 (GJB2) and GJB4 genes in autosomal recessive nonsyndromic hearing loss (ARNSHL) in South of Iran.

MATERIALS AND METHODS

A total of 36 large ARNSHL pedigrees with at least two affected subjects were enrolled in the current study. The GJB2 and GJB4 genes mutations were screened using direct sequencing method. The GJB2 and GJB4 negative families were analyzed for the linkage to DFNB21, DFNB24, DFNB29, and DFNB42 loci by genotyping the corresponding STR markers using polymerase chain reaction-PAGE method.

RESULTS

We found a homozygous nonsense mutation W77X and a homozygous missense mutation C169W in 5.55% of studied families in GJB2 and GJB4 genes, respectively. Five heterozygous mutations including V63G, A78T, and R127H in GJB2 gene, and R103C and R227W in GJB4 gene were detected. We identified two novel variations V63G in GJB2 and R227W in GJB4. In silico analysis predicted that both novel variations are deleterious mutations. We did not unveil any linkage between DFNB21, DFNB24, DFNB29, and DFNB42 loci and ARNSHL among studied families.

CONCLUSION

This is the first report of GJB2 and GJB4 mutations from Hormozgan population. According to the previous publications regarding GJB2 and GJB4 mutations, the distribution of the mutations is different from other parts of Iran that should be considered in primary health-care programs. Further investigations are needed to evaluate the contribution of other loci in ARNSHL subjects in South of Iran.