A study of deafness-related genetic mutations as a basis for strategies to prevent hereditary hearing loss in Hebei, China

Low frequency of SLC26A4 c.919-2A > G variant among patients with nonsyndromic hearing loss in Yunnan of Southwest China

BACKGROUND

Gene variants are responsible for more than half of hearing loss, particularly in nonsyndromic hearing loss (NSHL). The most common pathogenic variant in SLC26A4 gene found in East Asian populations is c.919-2A > G followed by c.2168A > G (p.H723R). This study was to evaluate their variant frequencies in patients with NSHL from special education schools in nine different areas of Southwest China's Yunnan.

METHODS

We performed molecular characterization by PCR-products directly Sanger sequencing of the SLC26A4 c.919-2AG and c.2168 A > G variants in 1167 patients with NSHL including 533 Han Chinese and 634 ethnic minorities.

RESULTS

The SLC26A4 c.919-2A > G variant was discovered in 8 patients with a homozygous state (0.69%) and twenty-five heterozygous (2.14%) in 1167 patients with NSHL. The total carrier rate of the c.919-2A > G variant was found in Han Chinese patients with 4.50% and ethnic minority patients with 1.42%. A significant difference existed between the two groups (P < 0.05). The c.919-2A > G allele variant frequency was ranged from 3.93% in Kunming to zero in Lincang and Nvjiang areas of Yunnan. We further detected the SLC26A4 c.2168 A > G variant in this cohort with one homozygotes (0.09%) and seven heterozygotes (0.60%), which was detected in Baoshan, Honghe, Licang and Pu`er areas. Between Han Chinese group (0.94%) and ethnic minority group (0.47%), there was no statistical significance (P > 0.05). Three Han Chinese patients (0.26%) carried compound heterozygosity for c.919-2A > G and c.2168 A > G.

CONCLUSION

These data suggest that the variants in both SLC26A4 c.919-2A > G and c.2168 A > G were relatively less frequencies in this cohort compared to the average levels in most regions of China, as well as significantly lower than that in Han-Chinese patients. These results broadened Chinese population genetic information resources and provided more detailed information for regional genetic counselling for Yunnan.

Case report: Novel GJB2 variant c.113T>C associated with autosomal recessive non-syndromic hearing loss (ARNSHL) in a Han family

RATIONALE

Molecular mechanism underlying the autosomal recessive non-syndromic hearing loss (ARNSHL) is still plausible. Pathogenic mutations of the gap junction beta 2 protein (GJB2) are reported to be the primary causes of ARNSHL.

PATIENT CONCERNS

A propositus was diagnosed as ARNSHL with bilateral congenital profound hearing loss.

DIAGNOSIS

With microarray and target gene sequencing testing methods, a novel GJB2 mutant was found to be associated with ARNSHL in this Han Chinese family.

INTERVENTIONS/OUTCOMES

Based on the finding in this research, prenatal screening of GJB2 mutation and genetic counseling are recommended to this family for their next pregnancy. Our interventions allow the family to plan informatively.

LESSONS

In this family, we discovered 2 heterozygous carriers of c.113T>C variation in the GJB2 gene. The propositus, who had profound hearing loss, had inherited the c.113T>C variation from his normal mother and the c.235delC from his father.

Mutation analysis of the SLC26A4 gene in three Chinese families

In order to investigate the genetic causes of hearing loss in a Chinese proband (in Family A) with enlarged vestibular aqueduct (EVA) and to investigate the genotype of two Chinese probands with SLC26A4 singe-allelic mutation and normal hearing (in Families B and C, respectively), the three probands and their parents were clinically and genetically evaluated. Twenty exons and flanking splice sites of the SLC26A4 gene were screened for pathogenic mutations via amplification with PCR and bidirectional sequencing. As controls, a group of 400 healthy newborns from the same ethnic background underwent SLC26A4 gene screening using the same method. The three probands all harbored two mutations in the SLC26A4 gene in the form of compound heterozygosity. The genotypes of mutations in Families A, B, and C are c.1211C>A/c.919-2A>G, c.1729G>A/c.919-2A>G, and c.1286C>A/c.919-2A>G, respectively. The missense mutations c.1211C>A (p.T430Q) in exon 10 and c.1729G>A (p.V577I) in exon 16 are both reported for the first time and were absent in 400 healthy newborns. c.1211C>A has Glutamine (Gln) at amino acid 430 instead of Threonine (Thr), and c.1729G>A has Isoleucine (Ile) at amino acid 577 instead of Valine (Val). c.1286C>A, a mutation previously reported in DVD and HGMD, was associated with Mondini deformity, but a proband with the c.1286C>A mutation in this study was normal. This study has demonstrated that the novel missense mutation c.1211C>A in compound heterozygosity with c.919-2A>G in the SLC26A4 gene is likely to be the cause of deafness in Family A. A novel variant, c.1729G>A, was identified and is likely benign. The pathogenicity of the c.1286C>A mutation warrants more in-depth study. These findings will broaden the spectrum of known SLC26A4 mutations in the Chinese population, providing more information for genetic counseling and diagnosis of hearing loss with EVA.

Mutation analysis of common deafness genes among 1,201 patients with non-syndromic hearing loss in Shanxi Province

Background

Hearing impairment is one of most frequent birth defects, which affects nearly 1 in every 1,000 live births. However, the molecular etiology of non‐syndromic deafness in China is not well studied. Here, we have investigated the presence of mutations in three genes commonly mutated in non‐syndromic deafness patients in Shanxi Province, which has the highest frequency of birth defects in China.

Methods

In total, 1,201 unrelated non‐syndromic deafness patients and 300 healthy individuals were enrolled. The hearing ability was confirmed by audiologic evaluation. Three major deafness‐related genes (GJB2, SLC26A4 (PDS), and mtDNA 12S rRNA) of all individuals enrolled were analyzed by Sanger sequencing.

Results

The results showed that GJB2 mutations accounted for 21.23% (255/1,201) in the patient group, with c.235delC, a hotspot mutation, accounting for 10.99% (132/1,201). Moreover, 11 new GJB2 mutations were identified. SLC26A4 mutations accounted for 9.33% (112/1,201) in the patient group, with IVS7‐2A>G as the most prevalent mutation accounting for 4.75% (57/1,201). In addition, 15 patients (1.25%) were found to carry mtDNA 12S rRNA c.1555A>G mutation, while only two cases had the mtDNA 12S rRNA c.1494C>T.

Conclusion

In our research, it was found that c.235delC in GJB2 and c.919‐2A>G (IVS7‐2A>G) in SLC26A4 were the highest frequency pathogenic variants in Shanxi Province. Taken together, our data will enrich the database of deafness mutations and will help clinical diagnosis, treatment, and genetic counseling of hearing impairment.

Genetic mutations in non-syndromic deafness patients in Hainan Province have a different mutational spectrum compared to patients from Mainland China

OBJECTIVES

To provide appropriate genetic testing and counseling for non-syndromic hearing impairment patients in Hainan Province, an island in the South China Sea.

METHODS

299 unrelated students with non-syndromic hearing loss who attended a special education school in Hainan Province were enrolled in this study. Three prominent deafness-related genes (GJB2, SLC26A4, and mtDNA 12S rRNA) were analyzed using Sanger sequencing.

RESULTS

GJB2 mutations were detected in 32.78% (98/299) of the entire cohort; however, only 5.69% (17/299) had two confirmed pathogenic mutations. The most common mutation observed in this population was c.109G > A in the GJB2 gene, with an allelic frequency of 15.05% (90/598), which is significantly higher than that reported in previous cohorts. A total of 16 patients had two confirmed pathogenic SLC26A4 gene mutations, and 16 patients had one. The IVS7-2A > G mutation was the most commonly observed, with an allelic frequency of 3.51% (21/598). Three patients had a m.1555A > G mutation in the mtDNA 12S rRNA gene.

CONCLUSIONS

These results reveal that genetic etiology occurred in 11.71% (35/299) of patients, suggesting that Hainan province have a different mutational spectrum compare to Mainland China in non-syndromic deafness patients, which provide useful information to genetic counseling in Hainan province.