Prevalence and range of GJB2 and SLC26A4 mutations in patients with autosomal recessive non-syndromic hearing loss

Mutation analysis of GJB2, SLC26A4, GJB3 and mtDNA12SrRNA genes in 251 non-syndromic hearing loss patients in Fujian, China

OBJECTIVES

The molecular etiology of non-syndromic hearing loss (NSHL) in Southeastern China (Fujian) has not been precisely identified. our study selected patients with NSHL and analyzed their causative genes, which helped to improve the accuracy of the diagnosis of hereditary hearing loss (HHL) and its treatment.

METHODS

251 unrelated patients who attended the otolaryngology clinic of Fujian Maternal and Child Health Hospital with hearing loss were enrolled to our study. All patients had genetic tests and listening tests, of which 251 were diagnosed with NSHL. In addition, we used whole-exome sequencing (WES) in a patient who has a significant family history of HHL but negative for gene chip testing, as well as in his family members.

RESULT

Among of 251 patients, Nucleotide changes were found in 63 cases (25.09%), including 34 located in GJB2(13.5%, including 235delC and 299_300delAT), 13 located in SLC26A4(5.18%, including c.919-2G > A and 2168 A > G), 1 located in GJB3(0.4%,538C > T) and 16 located in mtDNA12SrRNA (6.37%,1555 A > G). In addition, we discuss the process of identifying novel PLS1 mutations from 251 patients.

CONCLUSION

Our results demonstrate the conventional deafness gene mutation in 251 NSHL patients in Fujian, China. Compared with the other area of China, we have a lower detection rate, but GJB2 235delC remains the most common mutation in Fujian. In addition, we discuss the process of discovering novel mutation locus for deafness, which provides an understanding for deafness diagnosis and genetic testing.

Molecular diagnosis of SLC26A4-related hereditary hearing loss in a group of patients from two provinces of Iran

The SLC26A4 gene has been described as the second gene involved in most cases of autosomal recessive non-syndromic hearing loss (ARNSHL), after GJB2. Over 500 different SLC26A4 mutations have been reported, with each ethnic population having its own distinctive mutations. Here, we aimed to determine the frequency and mutation profile of the SLC26A4 gene from two different provinces (center and west) of Iran. This study included 50 nuclear families with two or more siblings segregating presumed ARNSHL. All affected tested negative for mutations in GJB2 at the DFNB1 locus and were therefore screened for autozygosity by descent using short tandem repeat polymorphisms (STRPs) of DFNB4. Sanger sequencing was performed to screen the 20 exons of the SLC26A4 gene for the families linked to this locus. In silico analyses were also performed using available software tools. Four out of 25 (16%) and 3 of 25 (12%) studied families of Isfahan and Hamedan provinces, respectively. were linked to DFNB4. Sanger sequencing led to the identification of six different mutations, one of which (c.919-2A>G) was recurrent and accounted for 31% of all mutant alleles. One out of 7 (14.3%) families with mutations were confirmed to be Pendred syndrome (PS). The SLC26A4 mutations have a high carrying rate in ARNSHL Iranian patients. The identification of a disease causing mutation can be used to establish a genotypic diagnosis and provide important information to the patients and their families.

[Enlarged vestibular aqueduct syndrome-dehiscence syndromes-honeycomb mastoid : Pathophysiology and evidence for clinical differentiation]

BACKGROUND

Differential diagnosis of dizziness with hearing loss requires standardized procedures for detection and classification of rare congenital and acquired malformations of the petrous part of the temporal bone.

OBJECTIVE

The aim of this study was to present the physiology and pathophysiology of endolymphatic and perilymphatic pressure regulation, diagnostic guidelines, and aspects of prognosis and treatment.

MATERIALS AND METHODS

Relevant publications and guidelines were evaluated and own cases are reported.

RESULTS

Enlarged vestibular aqueduct (EVA) is the most frequently observed malformation of the inner ear, which leads to increased internal hydrostatic pressure and cochleovestibular dysfunction. Non-syndromic and syndromic forms, e.g., Pendred syndrome, are known. Other pressure-relevant malformations are semicircular canal dehiscence syndrome (SCDS) and enlargement of the cochlear aqueduct. There are currently no treatment options for EVAS and enlarged cochlear aqueduct. Pendred syndrome generally requires treatment with cochlea implants (CI) in early childhood. Dizziness and autophony in patients with SCDS syndrome can be effectively treated by semicircular canal occlusion and coverage.

CONCLUSION

Complaints in non-syndromic EVA and SCD syndrome are mainly caused by exposure of the inner ear to provoked and spontaneous pressure increases. Deafness and vestibular dysfunction in syndromic EVA (i.e., Pendred syndrome, branchiootorenal syndrome) are caused by malformation of the cochlea, genetic maldevelopment of the hair cells, and pressure effects.

Deafness Gene Mutations in Newborns in the Foshan Area of South China With Bloodspot-Based Genetic Screening Tests

Purpose The aim of this study was to determine the rate of deafness gene mutations in the Foshan area of South China. Method We enrolled the infants delivered in Foshan Maternity and Children's Healthcare Hospital. Deafness gene mutation was detected by HibriMax method. Our study tested 47,538 newborns within 3 days after birth, including 13 sites in four genes: GJB2 (c.35 del G, c.176 del 16, c.235 del C, c.299 del AT, c.155 del TCTG), GJB3 (c.583 C>T), SLC26A4 (c.2168 A>G, c.919-2 A>G, c.1299 C>T), and mtDNA 12S rRNA (m.1555 A>G, m.1494 C>T, m.12201 T>C, m.7445 A>G). The birth condition of infants was collected, including sex, low or high birth weight, twins, and premature delivery. Results In a total of 47,538 newborns, 1,415 were positively identified with deafness gene mutations. The total rate of the deafness gene mutation was 2.976%. The carrier rates of GJB2 (c.35 del G, c.176 del 16, c.235 del C, c.299 del AT, c.155 del TCTG), GJB3 (c.583 C>T), SLC26A4 (c.2168 A>G, c.919-2 A>G, c.1299 C>T), and mtDNA 12S rRNA (m.1555 A>G, m.1494 C>T, m.12201 T>C, m.7445 A>G) mutations were 0.000%, 0.048%, 1.422%, 0.185%, 0.000%, 0.076%, 0.116%, 0.755%, 0.160%, 0.187%, 0.021%, 0.000%, and 0.006%, respectively. Conclusions Our study showed that the c.235 del C GJB2 mutation was the leading deafness-related mutation in the Foshan area of South China. Deafness gene mutations screening in newborns detected by bloodspot-based genetic screening tests can help the diagnosis of newborn congenital hearing loss.

GJB2 and GJB6 Mutations in Non-Syndromic Childhood Hearing Impairment in Ghana

Our study aimed to investigate GJB2 (connexin 26) and GJB6 (connexin 30) mutations associated with non-syndromic childhood hearing impairment (HI) as well as the environmental causes of HI in Ghana. Medical reports of 1,104 students attending schools for the deaf were analyzed. Families segregating HI, as well as isolated cases of HI of putative genetic origin were recruited. DNA was extracted from peripheral blood followed by Sanger sequencing of the entire coding region of GJB2. Multiplex PCR and Sanger sequencing were used to analyze the prevalence of GJB6-D3S1830 deletion. Ninety-seven families segregating HI were identified, with 235 affected individuals; and a total of 166 isolated cases of putative genetic causes, were sampled from 11 schools for the deaf in Ghana. The environmental factors, particularly meningitis, remain a major cause of HI impairment in Ghana. The male/female ratio was 1.49. Only 59.6% of the patients had their first comprehensive HI test between 6 to 11 years of age. Nearly all the participants had sensorineural HI (99.5%; n = 639). The majority had pre-lingual HI (68.3%, n = 754), of which 92.8% were congenital. Pedigree analysis suggested autosomal recessive inheritance in 96.9% of the familial cases. GJB2-R143W mutation, previously reported as founder a mutation in Ghana accounted for 25.9% (21/81) in the homozygous state in familial cases, and in 7.9% (11/140) of non-familial non-syndromic congenital HI cases, of putative genetic origin. In a control population without HI, we found a prevalent of GJB2-R143W carriers of 1.4% (2/145), in the heterozygous state. No GJB6-D3S1830 deletion was identified in any of the HI patients. GJB2-R143W mutation accounted for over a quarter of familial non-syndromic HI in Ghana and should be investigated in clinical practice. The large connexin 30 gene deletion (GJB6-D3S1830 deletion) does not account for of congenital non-syndromic HI in Ghana. There is a need to employ next generation sequencing approaches and functional genomics studies to identify the other genes involved in most families and isolated cases of HI in Ghana.

Mutation analysis of common deafness-causing genes among 506 patients with nonsyndromic hearing loss from Wenzhou city, China

OBJECTIVES

The frequency and spectrum of mutations in deafness-causing genes differs significantly according to the ethnic population and region under investigation. The molecular etiology of nonsyndromic hearing loss (NSHL) in Wenzhou, China, has not yet been systematically elucidated. To provide accurate genetic testing and counseling in this area, we investigated the molecular etiology of NSHL in a deaf population from Wenzhou.

METHODS

A total 506 unrelated patients with NSHL were enrolled in this study. Nine hotspot mutations in four major deafness genes were investigated by sequencing (Group I: 187 patients enrolled between 2011 and 2015) or allele-specific PCR-based universal array (Group II: 319 patients enrolled between 2016 and 2017). The investigated genes included GJB2 (c.35delG, c.176_191del16, c.235delC, c.299-300delAT), SLC26A4 (c.2168A > G, c.919-2A > G), mtDNA 12SrRNA (m.1555A > G, m.1494C > T), and GJB3 (c.538C > T). Furthermore, whole coding region sequencing or improved multiplex ligation detection reaction (IMLDR) were performed for patients who carried mono-allelic variants of GJB2 and SLC26A4, in order to detect other mutations among these patients.

RESULTS

GJB2 mutations were detected in 22.92% (116/506) of the entire cohort and SLC26A4 mutations were found in 6.52% (33/506) of the cohort. GJB3 mutations were detected in 0.79% (4/506) of the cohort. The mutation rate of mitochondrial DNA 12SrRNA in our patients was 17.40% (88/506), including 17.00% (86/506) with the m.1555A > G mutation and 0.40% (2/506) with the m.1494C > T mutation. The allelic frequency of the c.235delC mutation was 14.62% (148/1012), which is significantly higher than that of c.109G > A (33/1012, 3.26%), c.299_300delAT (13/1012, 1.28%), and c.176_191del16 (6/1012, 0.59%). The most common pathogenic mutation of SLC26A4 was the c.919-2A > G mutation (37/1012, 3.66%), followed by c.2168A > G (6/1012, 0.59%), and c.1229C > T (4/1012, 0.40%). Moreover, five rare pathogenic variants of GJB2 and eight rare pathogenic variants of SLC26A4 were identified.

CONCLUSION

GJB2 is the primary deafness-causing gene in deaf patients from Wenzhou, China; this is consistent with what is observed in most Chinese populations. However, the surprisingly high rate of the m.1555A > G mutation (17.00%) in patients from Wenzhou was significantly higher than in other populations in China. These findings highlight the specificity of the common deafness-causing gene mutation spectrum in the Wenzhou area. This information may be of benefit for genetic counseling and risk assessment for deaf patients from this area.

Elucidation of the unique mutation spectrum of severe hearing loss in a Vietnamese pediatric population

The mutational spectrum of deafness in Indochina Peninsula, including Vietnam, remains mostly undetermined. This significantly hampers the progress toward establishing an effective genetic screening method and early customized rehabilitation modalities for hearing loss. In this study, we evaluated the genetic profile of severe-to-profound hearing loss in a Vietnamese pediatric population using a hierarchical genetic analysis protocol that screened 11 known deafness-causing variants, followed by massively parallel sequencing targeting 129 deafness-associated genes. Eighty-seven children with isolated severe-to-profound non-syndromic hearing loss without family history were included. The overall molecular diagnostic yield was estimated to be 31.7%. The mutational spectrum for severe-to-profound non-syndromic hearing loss in our Vietnamese population was unique: The most prevalent variants resided in the MYO15A gene (7.2%), followed by GJB2 (6.9%), MYO7A (5.5%), SLC26A4 (4.6%), TMC1 (1.8%), ESPN (1.8%), POU3F4 (1.8%), MYH14 (1.8%), EYA1 (1.8%), and MR-RNR1 (1.1%). The unique spectrum of causative genes in the Vietnamese deaf population was similar to that in the southern Chinese deaf population. It is our hope that the mutation spectrum provided here could aid in establishing an efficient protocol for genetic analysis of severe-to-profound hearing loss and a customized screening kit for the Vietnamese population.

A Mutational Analysis of GJB2, SLC26A4, MT-RNA1, and GJB3 in Children with Nonsyndromic Hearing Loss in the Henan Province of China

BACKGROUND

Hearing impairment is one of the most common neurosensory disorders afflicting humans. Approximately half of all cases have a genetic etiology. The distribution and frequency of genetic mutations that cause deafness differ significantly by ethnic group and geographic region.

METHODS

130 sporadic nonsyndromic hearing loss (NSHL) children from the Henan province were subjected to microarray-based mutation detection. Nine pathogenic mutations were detected in four of the most common deafness-related genes (GJB2, GJB3, SLC26A4, and MT-RNA1).

RESULTS

Fifty percent of the analyzed patients (65/130) were shown to have genetic defects known to be related to deafness. Slightly >30% (41/130) had biallelic pathogenic mutations. One patient had pathogenic mutations in their mitochondrial genes (MT-RNA1); no mutations were detected in the GJB3 gene. Twenty-three (17.69%) patients were carriers of a single mutation in a recessive gene; these findings alone, however, cannot be interpreted as a cause of hearing loss. Utilizing this molecular strategy, we were able to arrive at a conclusive diagnosis for 42 of the NSHL children.

CONCLUSION

Genetic factors play a major role in sporadic NSHL patients from the Henan province, but it is clear that our screen needs to be expanded to include additional genes and alleles. Screening of potential pathogenic genes is important for patient risk assessment.

Application of SNPscan in Genetic Screening for Common Hearing Loss Genes

The current study reports the successful application of a fast and efficient genetic screening system for common hearing loss (HL) genes based on SNPscan genotyping technology. Genetic analysis of 115 variants in common genes related to HL, GJB2, SLC26A4 and MT-RNR, was performed on 695 subjects with non-syndromic hearing loss (NSHL) from the Northern China. The results found that 38.7% (269/695) of cases carried bi-allelic pathogenic variants in GJB2 and SLC26A4 and 0.7% (5/695) of cases carried homoplasmic MT-RNR1 variants. The variant allele frequency of GJB2, SLC26A4 and MT-RNR1 was 19.8% (275/1390), 21.9% (304/1390), and 0.86% (6/695), respectively. This approach can explain ~40% of NSHL cases and thus is a useful tool for establishing primary molecular diagnosis of NSHL in clinical genetics.

The homozygote p.V27I/p.E114G variant of GJB2 is a putative indicator of nonsyndromic hearing loss in Chinese infants

The gap junction β2 (GJB2) gene is associated with more than half of the recessive forms of hereditary hearing loss (HHL). However, the correlation between p.V27I and p.E114G variants of GJB2 and hearing phenotype remains controversial. This study aimed to clarify possible roles of these variants in Chinese infants with nonsyndromic hearing loss (NSHL). Hearing and gene tests were conducted in 300 infants (aged 0-3 months) with NSHL and 484 normal infants (aged 0-3 months). The p.V27I and p.E114G variants appeared frequently in both NSHL patients and normal controls. The allele and haplotype frequencies of p.V27I and p.E114G in patients and controls were compared, but no significant difference was observed (p=0.44 and p=0.26, respectively). Moreover, genotype frequencies of the p.V27I variant showed no significant difference between the two groups (p=0.66). Interestingly, more homozygote p.V27I/p.E114G subjects were found in NSHL infants than in controls (5/484 and 13/300, respectively), most of whom (61.54%) had mild or moderate hearing losses. Our results indicate that homozygote p.V27I/p.E114G is associated with mild and moderate HHL.

Prevalence and audiological profiles of GJB2 mutations in a large collective of hearing impaired patients

Mutations in the GJB2 gene are known to represent the commonest cause of hereditary and congenital hearing loss. In this study, a complete sequencing of the GJB2 gene in a cohort of 506 patients from a single, large cochlear implant program in Europe was performed. Audiological testing for those patients who could actively participate was performed using pure tone audiometry (PTA). Those unable to undergo PTA were measured using click-auditory brainstem response (ABR). Data analysis was performed to determine genotype-phenotype correlations of the mutational status vs. audiological profiles and vs. age at the time of presentation. An overall prevalence of biallelic mutations of 13.4% was found for the total collective. When subsets of younger patients were examined, the prevalence increased to 27% of those up to age 18 and 35% of those up to age 5 at the time of testing, respectively. This increase was found to be highly significant (p < 0.001). Analysis of the mean PTA thresholds revealed a strong correlation between allele combination status and mean PTA (p = 0.021). The prevalence of simple heterozygotes was found to be approximately 10.1%, which is around 3.3 times the value expected in the general population. As GJB2 follows a recessive pattern of inheritance, the question arises as to why such a large fraction of simple heterozygotes was observed among the hearing impaired patients included in this study.