Abstract
The Cell Division-Cycle-14 gene encodes a dual-specificity phosphatase necessary in yeast for exit from mitosis. Numerous disparate roles of vertebrate Cell Division-Cycle-14 (CDC14A) have ...been proposed largely based on studies of cultured cancer cells in vitro. The in vivo functions of vertebrate CDC14A are largely unknown. We generated and analyzed mutations of zebrafish and mouse CDC14A, developed a computational structural model of human CDC14A protein and report four novel truncating and three missense alleles of CDC14A in human families segregating progressive, moderate-to-profound deafness. In five of these families segregating pathogenic variants of CDC14A, deaf males are infertile, while deaf females are fertile. Several recessive mutations of mouse Cdc14a, including a CRISPR/Cas9-edited phosphatase-dead p.C278S substitution, result in substantial perinatal lethality, but survivors recapitulate the human phenotype of deafness and male infertility. CDC14A protein localizes to inner ear hair cell kinocilia, basal bodies and sound-transducing stereocilia. Auditory hair cells of postnatal Cdc14a mutants develop normally, but subsequently degenerate causing deafness. Kinocilia of germ-line mutants of mouse and zebrafish have normal lengths, which does not recapitulate the published cdc14aa knockdown morphant phenotype of short kinocilia. In mutant male mice, degeneration of seminiferous tubules and spermiation defects result in low sperm count, and abnormal sperm motility and morphology. These findings for the first time define a new monogenic syndrome of deafness and male infertility revealing an absolute requirement in vivo of vertebrate CDC14A phosphatase activity for hearing and male fertility.
ABSTRACT
Hereditary hearing loss is extremely heterogeneous. Over 70 genes have been identified to date, and with the advent of massively parallel sequencing, the pace of novel gene discovery has ...accelerated. In a family segregating progressive autosomal‐dominant nonsyndromic hearing loss (NSHL), we used OtoSCOPE® to exclude mutations in known deafness genes and then performed segregation mapping and whole‐exome sequencing to identify a unique variant, p.Ser178Leu, in TBC1D24 that segregates with the hearing loss phenotype. TBC1D24 encodes a GTPase‐activating protein expressed in the cochlea. Ser178 is highly conserved across vertebrates and its change is predicted to be damaging. Other variants in TBC1D24 have been associated with a panoply of clinical symptoms including autosomal recessive NSHL, syndromic hearing impairment associated with onychodystrophy, osteodystrophy, mental retardation, and seizures (DOORS syndrome), and a wide range of epileptic disorders.
After excluding mutations in all genes implicated in non‐syndromic hearing loss, we completed segregation mapping and whole exome sequencing on 7 and 3 persons, respectively. WES data were hard filtered to identify 46 variants shared by the 3 affecteds, only one of which mapped to a segregating genomic interval. The Ser178Leu variant in TBC1D24 is highly conserved across species. The transcribed gene is expressed in inner and outer hair cells in the P2 mouse cochlea (green; actin, red; DAPI, blue).
COCH
is the most abundantly expressed gene in the cochlea. Unsurprisingly, mutations in
COCH
underly hearing loss in mice and humans. Two forms of hearing loss are linked to mutations in
COCH
, the ...well-established autosomal dominant nonsyndromic hearing loss, with or without vestibular dysfunction (DFNA9) via a gain-of-function/dominant-negative mechanism, and more recently autosomal recessive nonsyndromic hearing loss (DFNB110) via nonsense variants. Using a combination of targeted gene panels, exome sequencing, and functional studies, we identified four novel pathogenic variants (two nonsense variants, one missense, and one inframe deletion) in
COCH
as the cause of autosomal recessive hearing loss in a multi-ethnic cohort. To investigate whether the non-truncating variants exert their effect via a loss-of-function mechanism, we used minigene splicing assays. Our data showed both the missense and inframe deletion variants altered RNA splicing by creating an exon splicing silencer and abolishing an exon splicing enhancer, respectively. Both variants create frameshifts and are predicted to result in a null allele. This study confirms the involvement of loss-of-function mutations in
COCH
in autosomal recessive nonsyndromic hearing loss, expands the mutational landscape of DFNB110 to include coding variants that alter RNA splicing, and highlights the need to investigate the effect of coding variants on RNA splicing.
The ClinGen Variant Curation Expert Panels (VCEPs) provide disease-specific rules for accurate variant interpretation. Using the hearing loss-specific American College of Medical Genetics and ...Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines, the Hearing Loss VCEP (HL VCEP) illustrates the utility of expert specifications in variant interpretation.
A total of 157 variants across nine HL genes, previously submitted to ClinVar, were curated by the HL VCEP. The curation process involved collecting published and unpublished data for each variant by biocurators, followed by bimonthly meetings of an expert curation subgroup that reviewed all evidence and applied the HL-specific ACMG/AMP guidelines to reach a final classification.
Before expert curation, 75% (117/157) of variants had single or multiple variants of uncertain significance (VUS) submissions (17/157) or had conflicting interpretations in ClinVar (100/157). After applying the HL-specific ACMG/AMP guidelines, 24% (4/17) of VUS and 69% (69/100) of discordant variants were resolved into benign (B), likely benign (LB), likely pathogenic (LP), or pathogenic (P). Overall, 70% (109/157) variants had unambiguous classifications (B, LB, LP, P). We quantify the contribution of the HL-specified ACMG/AMP codes to variant classification.
Expert specification and application of the HL-specific ACMG/AMP guidelines effectively resolved discordant interpretations in ClinVar. This study highlights the utility of ClinGen VCEPs in supporting more consistent clinical variant interpretation.
Recent advances in targeted genomic enrichment with massively parallel sequencing (TGE+MPS) have made comprehensive genetic testing for non‐syndromic hearing loss (NSHL) possible. After excluding ...NSHL subjects with causative mutations in GJB2 and the MT‐RNR1 (1555A>G) variant by Sanger sequencing, we completed TGE+MPS on 194 probands with presumed NSHL identified across Japan. We used both publicly available minor allele frequency (MAF) datasets and ethnic‐specific MAF filtering against an in‐house database of 200 normal‐hearing Japanese controls. Ethnic‐specific MAF filtering allowed us to re‐categorize as common 203 variants otherwise annotated as rare or novel in non‐Japanese ethnicities. This step minimizes false‐positive results and improves the annotation of identified variants. Causative variants were identified in 27% of probands with solve rates of 35%, 35% and 19% for dominant, recessive and sporadic NSHL, respectively. Mutations in MYO15A and CDH23 follow GJB2 as the frequent causes of recessive NSHL; copy number variations in STRC are a major cause of mild‐to‐moderate NSHL. Ethnic‐specific filtering by allele frequency is essential to optimize the interpretation of genetic data.
Hearing loss (HL) is one of the most common sensory defects affecting more than 466 million individuals worldwide. It is clinically and genetically heterogeneous with over 120 genes causing ...non‐syndromic HL identified to date. Here, we performed exome sequencing (ES) on a cohort of Iranian families with no disease‐causing variants in known deafness‐associated genes after screening with a targeted gene panel. We identified likely causal variants in 20 out of 71 families screened. Fifteen families segregated variants in known deafness‐associated genes. Eight families segregated variants in novel candidate genes for HL: DBH, TOP3A, COX18, USP31, TCF19, SCP2, TENM1, and CARMIL1. In the three of these families, intrafamilial locus heterogeneity was observed with variants in both known and novel candidate genes. In aggregate, we were able to identify the underlying genetic cause of HL in nearly 30% of our study cohort using ES. This study corroborates the observation that high‐throughput DNA sequencing in populations with high rates of consanguineous marriages represents a more appropriate strategy to elucidate the genetic etiology of heterogeneous conditions such as HL.
In this study, we performed exome sequencing on 71 families from a large cohort of Iranian hereditary hearing loss patients. For 70 out of 71 the GJB2 sequencing and targeted OtoSCOPE panel analysis were negative. We identified likely causal variants in 11 known deafness and eight novel candidate genes. Overall, we could resolve the underlying genetic cause for 28.1% of the previously unresolved families.
Hereditary deafness and retinal dystrophy are each genetically heterogenous and clinically variable. Three small unrelated families segregating the combination of deafness and retinal dystrophy were ...studied by exome sequencing (ES). The proband of Family 1 was found to be compound heterozygous for NM_004525.3: LRP2: c.5005A > G, p.(Asn1669Asp) and c.149C > G, p.(Thr50Ser). In Family 2, two sisters were found to be compound heterozygous for LRP2 variants, p.(Tyr3933Cys) and an experimentally confirmed c.7715 + 3A > T consensus splice‐altering variant. In Family 3, the proband is compound heterozygous for a consensus donor splice site variant LRP2: c.8452_8452 + 1del and p.(Cys3150Tyr). In mouse cochlea, Lrp2 is expressed abundantly in the stria vascularis marginal cells demonstrated by smFISH, single‐cell and single‐nucleus RNAseq, suggesting that a deficiency of LRP2 may compromise the endocochlear potential, which is required for hearing. LRP2 variants have been associated with Donnai–Barrow syndrome and other multisystem pleiotropic phenotypes different from the phenotypes of the four cases reported herein. Our data expand the phenotypic spectrum associated with pathogenic variants in LRP2 warranting their consideration in individuals with a combination of hereditary hearing loss and retinal dystrophy.
TMPRSS3
-related hearing loss presents challenges in correlating genotypic variants with clinical phenotypes due to the small sample sizes of previous studies. We conducted a cross-sectional genomics ...study coupled with retrospective clinical phenotype analysis on 127 individuals. These individuals were from 16 academic medical centers across 6 countries. Key findings revealed 47 unique
TMPRSS3
variants with significant differences in hearing thresholds between those with missense variants versus those with loss-of-function genotypes. The hearing loss progression rate for the DFNB8 subtype was 0.3 dB/year. Post-cochlear implantation, an average word recognition score of 76% was observed. Of the 51 individuals with two missense variants, 10 had DFNB10 with profound hearing loss. These 10 all had at least one of 4 TMPRSS3 variants predicted by computational modeling to be damaging to TMPRSS3 structure and function. To our knowledge, this is the largest study of TMPRSS3 genotype–phenotype correlations. We find significant differences in hearing thresholds, hearing loss progression, and age of presentation, by TMPRSS3 genotype and protein domain affected. Most individuals with TMPRSS3 variants perform well on speech recognition tests after cochlear implant, however increased age at implant is associated with worse outcomes. These findings provide insight for genetic counseling and the on-going design of novel therapeutic approaches.
Shin-ya Nishio 1 and Isabelle Schrauwen 2 and Hideaki Moteki 1 and Hela Azaiez 3 1, Shinshu University School of Medicine, Matsumoto, Nagano 390-8621, Japan 2, Translational Genomics Research ...Institute, Phoenix, AZ 85004, USA 3, Department of Otolaryngology, University of Iowa, Iowa City, IA 52246, USA Received 9 June 2016; Accepted 13 June 2016; 20 July 2016 This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In addition to NGS, recent progress in genome editing, embryonic stem cells, and induced pluripotent stem cells has opened a new gate to a fast and thorough characterization and understanding of the precise functions and mechanisms involved in the biology of hearing and deafness.
Hereditary hearing loss is a clinically and genetically heterogeneous disorder. More than 80 genes have been implicated to date, and with the advent of targeted genomic enrichment and massively ...parallel sequencing (TGE+MPS) the rate of novel deafness-gene identification has accelerated. Here we report a family segregating post-lingual progressive autosomal dominant non-syndromic hearing loss (ADNSHL). After first excluding plausible variants in known deafness-causing genes using TGE+MPS, we completed whole exome sequencing in three hearing-impaired family members. Only a single variant, p.Arg185Pro in HOMER2, segregated with the hearing-loss phenotype in the extended family. This amino acid change alters a highly conserved residue in the coiled-coil domain of HOMER2 that is essential for protein multimerization and the HOMER2-CDC42 interaction. As a scaffolding protein, HOMER2 is involved in intracellular calcium homeostasis and cytoskeletal organization. Consistent with this function, we found robust expression in stereocilia of hair cells in the murine inner ear and observed that over-expression of mutant p.Pro185 HOMER2 mRNA causes anatomical changes of the inner ear and neuromasts in zebrafish embryos. Furthermore, mouse mutants homozygous for the targeted deletion of Homer2 present with early-onset rapidly progressive hearing loss. These data provide compelling evidence that HOMER2 is required for normal hearing and that its sequence alteration in humans leads to ADNSHL through a dominant-negative mode of action.
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