Analysis of two Arab families reveals additional support for a DFNB2 nonsyndromic phenotype of MYO7A

Novel compound heterozygous synonymous and missense variants in the MYO7A gene identified by next-generation sequencing in a Chinese family with nonsyndromic hearing loss

BACKGROUND

Variants in the MYO7A gene are increasingly identified among patients suffering from Usher syndrome type 1B (USH1B). However, such mutations are less commonly detected among patients suffering from nonsyndromic hearing loss (NSHL), including autosomal recessive deafness (DFNB2) and autosomal dominant deafness (DFNA11). This research attempts to clarify the genetic base of DFNB2 in a Chinese family and determine the pathogenicity of the identified mutations.

METHOD

Targeted next-generation sequencing (TGS) of 127 known deafness genes was performed for the 14-year-old proband. Then, Sanger sequencing was performed on the available family members. A minigene splicing assay was performed to verify the impact of the novel MYO7A synonymous variant. After performing targeted next-generation sequencing (TGS) of 127 existing hearing loss-related genes in a 14-year-old proband, Sanger sequencing was carried out on the available family members. Then, to confirm the influence of the novel MYO7A synonymous variants, a minigene splicing assay was performed.

RESULTS

Two heteroallelic mutants of MYO7A (NM_000260.3) were identified: a maternally inherited synonymous variant c.2904G > A (p.Glu968=) in exon 23 and a paternally inherited missense variant c.5994G > T (p.Trp1998Cys) in exon 44. The in vitro minigene expression indicated that c.2904G > A may result in skipping of exon 23 resulting in a truncated protein.

CONCLUSIONS

We reported a novel missense (c.5994G > T) and identified, for the first time, a novel pathogenic synonymous (c.2904G > A) variant within MYO7A in a patient with DFNB2. These findings enrich our understanding of the MYO7A variant spectrum of DFNB2 and can contribute to accurate genetic counseling and diagnosis of NSHL patients.

Mutation spectrum of non-syndromic hearing loss in the UAE, a retrospective cohort study and literature review

BACKGROUND

Hearing loss (HL) is a heterogeneous condition that causes partial or complete hearing impairment. Hundreds of variants in >60 genes have been reported to be associated with Hereditary HL (HHL), variants of the GJB2 gene are the most common cause of congenital SNHL, with >100 variants reported. The HHL prevalence is thought to be high in the Arab population; however, the genetic epidemiology of HHL among Emirati populations is understudied.

AIMS

To shed light on the mutational spectrum of NSHL in Emirati patients seen in the genetic clinic over 10 years and to capture founder mutation(s) if any were identified.

METHODS

Retrospective chart review of all Emirati patients assessed by clinical geneticists due to NSHL during the period between January 2010 to December 2020. Genetic tests were done based on clinical phenotypes of the patient and family history including targeted mutation testing, next-generation sequencing, or whole-exome sequencing (solo or trio). The authors did literature reviews using PubMed for all previously reported articles related to NSHL genes from UAE.

RESULTS

A total of 162 patients with HL, were evaluated during the period between January 2010 to December 2020. There were 82 patients with NSHL, and only 72 patients who completed the genetic evaluations were included in this retrospective study. Among the studied group, 42 (51.2%) were males and 40 (48.78%) were females. The youngest patient was 2 years old and the oldest patient was 50 years old. Consanguinity was documented in 76 patients (92.68%). A total of 14 mutations reported here are novel (23/72 i.e., 31.9%). Twelve missense mutations, 6 nonsense mutations, 6 frameshift mutations, 2 in-frame deletion mutations, and 1 splice site mutation was found. Variants in the GJB2 gene are the most commonly identified cause of NSHL, with c.35delG being the most followed by c.506G > A. The second commonly found variant is c.934C > G (p.Arg312Gly) in the CDC14A gene, found in 9 patients. This was followed by variants in OTOF and SLC26A4 genes, found in 8 patients, respectively. Chromosomal microdeletions encompassing genes causing NSHL were found in 3 patients. No mitochondrial mutations were found in this study group. A total of 11 previous reports about Emirati patients with NSHL were reviewed, with a total of 35 patients.

CONCLUSION

Emirati patients with NSHL have several mutations, most notably missense mutations. Novel mutations are worth further testing and represent the area for future researches.

Putative Digenic GJB2/MYO7A Inheritance of Hearing Loss Detected in a Patient with 48,XXYY Klinefelter Syndrome

OBJECTIVES

Nonsyndromic hearing loss (NSHL) is the most frequent type of hereditary hearing impairment. Here, we explored the underlying genetic cause of NSHL in a three-generation family using whole-exome sequencing. The proband had concomitant NSHL and rare 48,XXYY Klinefelter syndrome.

MATERIAL AND METHODS

Genomic DNA was extracted from the peripheral blood of the proband and their family members. Sanger sequencing and pedigree verification were performed on the pathogenic variants filtered by whole-exome sequencing. The function of the variants was analyzed using bioinformatics software.

RESULTS

The proband was digenic heterozygous for p.V37I in the GJB2 gene and p.L347I in the MYO7A gene. The proband's mother had normal hearing and did not have any variant. The proband's father and uncle both had NSHL and were compound for the GJB2 p.V37I and MYO7A p.L347I variants, thus indicating a possible GJB2/MYO7A digenic inheritance of NSHL. 48,XXYY Klinefelter syndrome was discovered in the proband after the karyotype analysis, while his parents both had normal karyotypes.

CONCLUSIONS

Our findings reported a putative GJB2/MYO7A digenic inheritance form of hearing loss, expanding the genotype and phenotype spectrum of NSHL. In addition, this is the first report of concomitant NSHL and 48,XXYY syndrome.

Genetic Epidemiology of Hearing Loss in the 22 Arab Countries: A Systematic Review

BACKGROUND

Hearing loss (HL) is a heterogeneous condition that causes partial or complete hearing impairment. Hundreds of variants in more than 60 genes have been reported to be associated with Hereditary HL (HHL). The HHL prevalence is thought to be high in the Arab population; however, the genetic epidemiology of HHL among Arab populations is understudied. This study aimed to systematically analyze the genetic epidemiology of HHL in Arab countries.

METHODS

We searched four literature databases (PubMed, Scopus, Science Direct, and Web of Science) from the time of inception until January 2019 using broad search terms to capture all the reported epidemiological and genetic data related to Arab patients with HHL.

FINDINGS

A total of 2,600 citations were obtained; 96 studies met our inclusion criteria. Our search strategy yielded 121,276 individuals who were tested for HL over 52 years (1966-2018), of whom 8,099 were clinically diagnosed with HL and belonged to 16 Arab countries. A total of 5,394 patients and 61 families with HHL were genotyped, of whom 336 patients and 6 families carried 104 variants in 44 genes and were from 17/22 Arab countries. Of these variants, 72 (in 41 genes) were distinctive to Arab patients. Arab patients manifested distinctive clinical phenotypes. The incidence of HHL in the captured studies ranged from 1.20 to 18 per 1,000 births per year, and the prevalence was the highest in Iraq (76.3%) and the lowest in Jordan (1.5%).

INTERPRETATION

This is the first systematic review to capture the prevalence and spectrum of variants associated with HHL in an Arab population. There appears to be a distinctive clinical picture for Arab patients with HHL, and the range and distribution of variants among Arab patients differ from those noted in other affected ethnic groups.

Spectrum of MYO7A Mutations in an Indigenous South African Population Further Elucidates the Nonsyndromic Autosomal Recessive Phenotype of DFNB2 to Include Both Homozygous and Compound Heterozygous Mutations

MYO7A gene encodes unconventional myosin VIIA, which, when mutated, causes a phenotypic spectrum ranging from recessive hearing loss DFNB2 to deaf-blindness, Usher Type 1B (USH1B). MYO7A mutations are reported in nine DFNB2 families to date, none from sub-Saharan Africa.In DNA, from a cohort of 94 individuals representing 92 families from the Limpopo province of South Africa, eight MYO7A variations were detected among 10 individuals. Family studies identified homozygous and compound heterozygous mutations in 17 individuals out of 32 available family members. Four mutations were novel, p.Gly329Asp, p.Arg373His, p.Tyr1780Ser, and p.Pro2126Leufs*5. Two variations, p.Ser617Pro and p.Thr381Met, previously listed as of uncertain significance (ClinVar), were confirmed to be pathogenic. The identified mutations are predicted to interfere with the conformational properties of myosin VIIA through interruption or abrogation of multiple interactions between the mutant and neighbouring residues. Specifically, p.Pro2126Leufs*5, is predicted to abolish the critical site for the interactions between the tail and the motor domain essential for the autoregulation, leaving a non-functional, unregulated protein that causes hearing loss. We have identified MYO7A as a possible key deafness gene among indigenous sub-Saharan Africans. The spectrum of MYO7A mutations in this South African population points to DFNB2 as a specific entity that may occur in a homozygous or in a compound heterozygous state.

Global genetic insight contributed by consanguineous Pakistani families segregating hearing loss

Consanguineous Pakistani pedigrees segregating deafness have contributed decisively to the discovery of 31 of the 68 genes associated with nonsyndromic autosomal recessive hearing loss (HL) worldwide. In this study, we utilized genome-wide genotyping, Sanger and exome sequencing to identify 163 DNA variants in 41 previously reported HL genes segregating in 321 Pakistani families. Of these, 70 (42.9%) variants identified in 29 genes are novel. As expected from genetic studies of disorders segregating in consanguineous families, the majority of affected individuals (94.4%) are homozygous for HL-associated variants, with the other variants being compound heterozygotes. The five most common HL genes in the Pakistani population are SLC26A4, MYO7A, GJB2, CIB2 and HGF, respectively. Our study provides a profile of the genetic etiology of HL in Pakistani families, which will allow for the development of more efficient genetic diagnostic tools, aid in accurate genetic counseling, and guide application of future gene-based therapies. These findings are also valuable in interpreting pathogenicity of variants that are potentially associated with HL in individuals of all ancestries. The Pakistani population, and its infrastructure for studying human genetics, will continue to be valuable to gene discovery for HL and other inherited disorders.

Novel compound heterozygous MYO7A mutations in Moroccan families with autosomal recessive non-syndromic hearing loss

The MYO7A gene encodes a protein belonging to the unconventional myosin super family. Mutations within MYO7A can lead to either non syndromic hearing loss or to the Usher syndrome type 1B (USH1B). Here, we report the results of genetic analyses performed on Moroccan families with autosomal recessive non syndromic hearing loss that identified two families with compound heterozygous MYO7A mutations. Five mutations (c.6025delG, c.6229T>A, c.3500T>A, c.5617C>T and c.4487C>A) were identified in these families, the latter presenting two differently affected branches. Multiple bioinformatics programs and molecular modelling predicted the pathogenic effect of these mutations. In conclusion, the absence of vestibular and retinal symptom in the affected patients suggests that these families have the isolated non-syndromic hearing loss DFNB2 (nonsyndromic autosomal recessive hearing loss) presentation, instead of USH1B.

Bilateral Labyrinthine and Internal Auditory Canal Enhancement in an Infant With Severe Labyrinthine Dysplasia: A Previously Unreported Phenomenon

OBJECTIVE

To describe a novel case of congenital profound bilateral sensorineural hearing loss in a patient with bilateral nodular internal auditory canal and labyrinthine enhancement and temporal bone dysplasia.

PATIENTS

A 76-day-old female was referred to the authors' center for evaluation of congenital deafness. Behavioral observations and objective audiometric evaluation demonstrated bilateral profound sensorineural hearing loss and a comprehensive multidisciplinary evaluation identified compound heterozygous pathogenic variants in MYO7A, a gene associated with Usher Syndrome Type 1B or DFNB2. Computed tomography and contrast-enhanced magnetic resonance imaging studies demonstrated bilateral temporal bone anomalies with unique middle and inner ear malformations, as well as unique contrast enhancement in the membranous labyrinth, internal auditory canals, and cranial nerves, which have not been previously described with MYO7A variants.

INTERVENTIONS

Given the potential risk for progressive bilateral labyrinthitis ossificans, bilateral simultaneous cochlear implantation was performed at 4 months of age.

MAIN OUTCOME MEASURES

Subsequent audiologic follow up after implantation shows significantly improved access to auditory information and increased vocalizations. At last testing, speech and language skills for both receptive and expressive language abilities were found to be commensurate with her chronological age.

CONCLUSION

We report a novel presentation and imaging findings of congenital bilateral profound sensorineural hearing loss in a patient with nodular internal auditory canal and labyrinthine enhancement and coexisting inner ear dysplasia. Despite the multiple radiologic abnormalities, the patient has demonstrated good benefit from cochlear implantation. Future study of rare variants of congenital deafness, such as this, is critical toward defining new disease processes and determining optimal treatment.

Novel compound heterozygous mutations in MYO7A gene associated with autosomal recessive sensorineural hearing loss in a Chinese family

OBJECTIVES

Mutations in MYO7A gene have been reported to be associated with Usher Syndrome type 1B (USH1B) and nonsyndromic hearing loss (DFNB2, DFNA11). Most mutations in MYO7A gene caused USH1B, whereas only a few reported mutations led to DFNB2 and DFNA11. The current study was designed to investigate the mutations among a Chinese family with autosomal recessive hearing loss.

METHODS

In this study, we present the clinical, genetic and molecular characteristics of a Chinese family. Targeted capture of 127 known deafness genes and next-generation sequencing were employed to study the genetic causes of two siblings in the Chinese family. Sanger sequencing was employed to examine those variant mutations in the members of this family and other ethnicity-matched controls.

RESULTS

We identified the novel compound heterozygous mutant alleles of MYO7A gene: a novel missense mutation c.3671C>A (p.A1224D) and a reported insert mutation c.390_391insC (p.P131PfsX9). Variants were further confirmed by Sanger sequencing. These two compound heterozygous variants were co-segregated with autosomal recessive hearing loss phenotype. The gene mutation analysis and protein sequence alignment further supported that the novel compound heterozygous mutations were pathogenic.

CONCLUSION

The novel compound heterozygous mutations (c.3671C>A and c.390_391insC) in MYO7A gene identified in this study were responsible for the autosomal recessive sensorineural hearing loss of this Chinese family.

Mutations of human NARS2, encoding the mitochondrial asparaginyl-tRNA synthetase, cause nonsyndromic deafness and Leigh syndrome

Here we demonstrate association of variants in the mitochondrial asparaginyl-tRNA synthetase NARS2 with human hearing loss and Leigh syndrome. A homozygous missense mutation ([c.637G>T; p.Val213Phe]) is the underlying cause of nonsyndromic hearing loss (DFNB94) and compound heterozygous mutations ([c.969T>A; p.Tyr323*] + [c.1142A>G; p.Asn381Ser]) result in mitochondrial respiratory chain deficiency and Leigh syndrome, which is a neurodegenerative disease characterized by symmetric, bilateral lesions in the basal ganglia, thalamus, and brain stem. The severity of the genetic lesions and their effects on NARS2 protein structure cosegregate with the phenotype. A hypothetical truncated NARS2 protein, secondary to the Leigh syndrome mutation p.Tyr323* is not detectable and p.Asn381Ser further decreases NARS2 protein levels in patient fibroblasts. p.Asn381Ser also disrupts dimerization of NARS2, while the hearing loss p.Val213Phe variant has no effect on NARS2 oligomerization. Additionally we demonstrate decreased steady-state levels of mt-tRNA^Asn in fibroblasts from the Leigh syndrome patients. In these cells we show that a decrease in oxygen consumption rates (OCR) and electron transport chain (ETC) activity can be rescued by overexpression of wild type NARS2. However, overexpression of the hearing loss associated p.Val213Phe mutant protein in these fibroblasts cannot complement the OCR and ETC defects. Our findings establish lesions in NARS2 as a new cause for nonsyndromic hearing loss and Leigh syndrome.

Mitochondrial respiratory chain (MRC) disease represents a large and heterogeneous group of energy deficiency disorders. Here we report three mutations in NARS2, a mitochondrial asparaginyl-tRNA synthetase, associated with non-syndromic hearing loss (NSHL) and Leigh syndrome in two independent families. Located in the predicted catalytic domain of the protein, missense mutation p.(Val213Phe) results in NSHL (DFNB94) while compound heterozygous mutation (p.Tyr323*; p.Asn381Ser) is leading to Leigh syndrome with auditory neuropathy. In vivo analysis deemed p.Tyr323* mutant protein to be unstable. Co-immunoprecipitation assays show that p.Asn381Ser mutant disrupts the dimerization ability of NARS2. Leigh syndrome patient fibroblasts exhibit a decreased steady-state level of mt-tRNA^Asn. In addition, in these cells, the mitochondrial respiratory chain is deficient, including significantly decreased oxygen consumption rates and electron transport chain activities. These functions can be partially restored with over-expression of wild-type NARS2 but not with p.Val213Phe mutant protein. Our study provides new insights into the genes that are necessary for the function of brain and inner ear sensory cells in humans.