Confirmation of COL4A6 variants in X-linked nonsyndromic hearing loss and its clinical implications.

Hearing loss (HL) is one of the most common sensory defects, of which X-linked nonsyndromic hearing loss (NSHL) accounts for only 1-2%. While a COL4A6 variant has been reported in a single Hungarian family with NSHL associated with inner ear malformation, causative role of COL4A6 variants and their phenotypic consequences in NSHL remain elusive. Here we report two families in which we identified a male member with X-linked HL. Each has inherited a rare hemizygous COL4A6 variant from their respective mothers, NM_001287758.1: c.3272 G > C (p.Gly1091Ala) and c.951 + 1 G > C. An in vitro minigene splicing assay revealed that c.951 + 1 G > T leads to skipping of exon 15, strongly suggesting a pathogenic role for this variant in the HL phenotype. The p.Gly1091Ala variant is classified as a variant of unknown significance based on the variant interpretation guidelines. This report provides evidence for variants in the COL4A6 gene resulting in X-linked NSHL. It highlights the importance of in-depth genetic studies in all family members in addition to the proband, especially in multiplex families, to determine the precise etiology of HL.

Analyses of del(GJB6-D13S1830) and del(GJB6-D13S1834) deletions in a large cohort with hearing loss: Caveats to interpretation of molecular test results in multiplex families.

BACKGROUND: Mutations involving the closely linked GJB2 and GJB6 at the DFNB1 locus are a common genetic cause of profound congenital hearing loss in many populations. In some deaf GJB2 heterozygotes, a 309 kb deletion involving the GJB6 has been found to be the cause for hearing loss when inherited in trans to a GJB2 mutation. METHODS: We screened 2,376 probands from a National DNA Repository of deaf individuals. RESULTS: Fifty-two of 318 heterozygous probands with pathogenic GJB2 sequence variants had a GJB6 deletion. Additionally, eight probands had an isolated heterozygous GJB6 deletion that did not explain their hearing loss. In two deaf subjects, including one proband, a homozygous GJB6 deletion was the cause for their hearing loss, a rare occurrence not reported to date. CONCLUSION: This study represents the largest US cohort of deaf individuals harboring GJB2 and GJB6 variants, including unique subsets of families with deaf parents. Testing additional members to clarify the phase of GJB2/GJB6 variants in multiplex families was crucial in interpreting clinical significance of the variants in the proband. It highlights the importance of determining the phase of GJB2/GJB6 variants when interpreting molecular test results especially in multiplex families with assortative mating.

Loss of LDAH associated with prostate cancer and hearing loss.

Great strides in gene discovery have been made using a multitude of methods to associate phenotypes with genetic variants, but there still remains a substantial gap between observed symptoms and identified genetic defects. Herein, we use the convergence of various genetic and genomic techniques to investigate the underpinnings of a constellation of phenotypes that include prostate cancer (PCa) and sensorineural hearing loss (SNHL) in a human subject. Through interrogation of the subject's de novo, germline, balanced chromosomal translocation, we first identify a correlation between his disorders and a poorly annotated gene known as lipid droplet associated hydrolase (LDAH). Using data repositories of both germline and somatic variants, we identify convergent genomic evidence that substantiates a correlation between loss of LDAH and PCa. This correlation is validated through both in vitro and in vivo models that show loss of LDAH results in increased risk of PCa and, to a lesser extent, SNHL. By leveraging convergent evidence in emerging genomic data, we hypothesize that loss of LDAH is involved in PCa and other phenotypes observed in support of a genotype-phenotype association in an n-of-one human subject.

American College of Medical Genetics and Genomics guideline for the clinical evaluation and etiologic diagnosis of hearing loss.

Hearing loss is a common and complex condition that can occur at any age, can be inherited or acquired, and is associated with a remarkably wide array of etiologies. The diverse causes of hearing loss, combined with the highly variable and often overlapping presentations of different forms of hearing loss, challenge the ability of traditional clinical evaluations to arrive at an etiologic diagnosis for many deaf and hard-of-hearing individuals. However, identifying the etiology of a hearing loss may affect clinical management, improve prognostic accuracy, and refine genetic counseling and assessment of the likelihood of recurrence for relatives of deaf and hard-of-hearing individuals. Linguistic and cultural identities associated with being deaf or hard of hearing can complicate access to and the effectiveness of clinical care. These concerns can be minimized when genetic and other health-care services are provided in a linguistically and culturally sensitive manner. This guideline offers information about the frequency, causes, and presentations of hearing loss and suggests approaches to the clinical evaluation of deaf and hard-of-hearing individuals aimed at identifying an etiologic diagnosis and providing informative and effective patient education and genetic counseling.

The clinical and audiologic features of hearing loss due to mitochondrial mutations.

OBJECTIVES: To characterize mitochondrial sequence variants present in a nationwide hereditary deafness DNA repository of samples from deaf subjects and to define the clinical presentation and audiometric characteristics of individuals with a mitochondrial sequence variant. STUDY DESIGN: Retrospective review of results for select mitochondrial mutations performed on DNA samples from subjects compiled from 1997 to 2009. SETTING: National hereditary deafness DNA repository. SUBJECTS AND METHODS: Available samples from subjects in the repository were screened to identify those with mitochondrial sequence variants. Clinical data on the nature of mutation, type and severity of the hearing loss, and sex, age at diagnosis, family history of hearing loss, and ethnicity were analyzed. RESULTS: Eighty-six patients were identified with mitochondrial mutations or 3.5% of the subjects studied. Among those with mitochondrial mutations, 21 (24.4%) had the m.7445A>G substitution, 18 (20.9%) had the m.1555A>G substitution, 18 (20.9%) had the m.961T>G substitution, and 29 (33.7%) had a m.961delT+C(n) complex deletion. The majority of patients had bilateral severe to profound hearing loss. Fifty-three (62%) patients were female, and a family history of hearing loss was documented in 66 (76.7%) patients. The deafness was recognized prior to 3 years of age in 26 patients. CONCLUSION: Mitochondrial deafness in this sample was associated with a variety of genetic mutations and a wide spectrum of clinical presentations. Because of increased aminoglycoside susceptibility associated with some forms of mitochondrial deafness, matrilineal relatives may be at risk in those cases, highlighting the importance of making an accurate diagnosis prior to exposure.

Etiology of unilateral hearing loss in a national hereditary deafness repository.

PURPOSE: The aim of this study was to characterize the genetic, audiologic, and epidemiologic characteristics of unilateral hearing loss (HL) in a national hereditary deafness repository. MATERIALS AND METHODS: This is a prospective clinical study involving 34 subjects identified in a national hereditary deafness repository. Clinical data and family history of HL were obtained on enrollment. Candidate deafness genes were screened by single-stranded conformation polymorphism, and mutations were confirmed with sequencing. RESULTS: Thirty-four subjects (19 males, 15 females) with unilateral HL were identified, ranging in age from 2 months to 36 years. The mean age at diagnosis was 7 years, and the left ear was affected in 62% of the cases. The racial distribution of our sample was 62% white, 23% African American, and 15% Hispanic. Imaging results were available in 47%, and most (69%) were considered normal. Nineteen percent had enlarged vestibular aqueducts, 2 had ipsilateral Mondini dysplasia, and 1 had a common cavity deformity. Twenty subjects (59%) had a family history of HL, with 26% specifically reporting familial unilateral HL. Mutational screening revealed sequence variants in the GJB2 (connexin 26), GJB3 (connexin 31), TECTA, and COCH genes. Two novel mutations were detected in COCH and TECTA. CONCLUSIONS: Sequence variants in known deafness genes were detected in more than one-third of our study population, suggesting that gene/gene or gene/environmental interactions may indeed play a role in the etiology of some cases of unilateral deafness. Further prospective studies including congenital cytomegalovirus screening at birth and molecular screening of deafness genes in children with congenital unilateral HL will be required to establish the etiology of unilateral deafness with certainty.

Identification of p.A684V missense mutation in the WFS1 gene as a frequent cause of autosomal dominant optic atrophy and hearing impairment.

Optic atrophy (OA) and sensorineural hearing loss (SNHL) are key abnormalities in several syndromes, including the recessively inherited Wolfram syndrome, caused by mutations in WFS1. In contrast, the association of autosomal dominant OA and SNHL without other phenotypic abnormalities is rare, and almost exclusively attributed to mutations in the Optic Atrophy-1 gene (OPA1), most commonly the p.R445H mutation. We present eight probands and their families from the US, Sweden, and UK with OA and SNHL, whom we analyzed for mutations in OPA1 and WFS1. Among these families, we found three heterozygous missense mutations in WFS1 segregating with OA and SNHL: p.A684V (six families), and two novel mutations, p.G780S and p.D797Y, all involving evolutionarily conserved amino acids and absent from 298 control chromosomes. Importantly, none of these families harbored the OPA1 p.R445H mutation. No mitochondrial DNA deletions were detected in muscle from one p.A684V patient analyzed. Finally, wolframin p.A684V mutant ectopically expressed in HEK cells showed reduced protein levels compared to wild-type wolframin, strongly indicating that the mutation is disease-causing. Our data support OA and SNHL as a phenotype caused by dominant mutations in WFS1 in these additional eight families. Importantly, our data provide the first evidence that a single, recurrent mutation in WFS1, p.A684V, may be a common cause of ADOA and SNHL, similar to the role played by the p.R445H mutation in OPA1. Our findings suggest that patients who are heterozygous for WFS1 missense mutations should be carefully clinically examined for OA and other manifestations of Wolfram syndrome.

Vestibular dysfunction in DFNB1 deafness.

Mutations of GJB2 and GJB6 (connexin-26 and 30) at the DFNB1 locus are the most common cause of autosomal recessive, nonsyndromic deafness. Despite their widespread expression throughout the vestibular system, vestibular dysfunction has not been widely recognized as a commonly associated clinical feature. The observations of vertigo accompanying DFNB1 deafness in several large families prompted our hypothesis that vestibular dysfunction may be an integral, but often overlooked, component of DFNB1 deafness. Our aim was to define the prevalence of vestibular dysfunction in Cases of DFNB1 deafness and Controls with other forms of deafness. We developed and used a survey to assess symptoms of vestibular dysfunction, medical, and family history was distributed to Cases with deafness due to pathogenic GJB2 and/or GJB6 mutations and deaf Controls without DFNB1 deafness. Our results showed: Surveys were returned by 235/515 Cases (46%) with DFNB1 mutations and 121/321 Controls (38%) without these mutations. The mean age of Cases (41) was younger than Controls (51; P < 0.001). Vestibular dysfunction was reported by 127 (54%) of Cases and was present at significantly higher rates in Cases than in deaf Controls without DFNB1 deafness (P < 0.03). Most (63%) had to lie down in order for vertigo to subside, and 48% reported that vertigo interfered with activities of daily living. Vertigo was reported by significantly more Cases with truncating than non-truncating mutations and was also associated with a family history of dizziness. We conclude that vestibular dysfunction appears to be more common in DFNB1 deafness than previously recognized and affects activities of daily living in many patients.

Fitness among individuals with early childhood deafness: Studies in alumni families from Gallaudet University.

The genetic fitness of an individual is influenced by their phenotype, genotype and family and social structure of the population in which they live. It is likely that the fitness of deaf individuals was quite low in the Western European population during the Middle Ages. The establishment of residential schools for deaf individuals nearly 400 years ago resulted in relaxed genetic selection against deaf individuals which contributed to the improved fitness of deaf individuals in recent times. As part of a study of deaf probands from Gallaudet University, we collected pedigree data, including the mating type and the number and hearing status of the children of 686 deaf adults and 602 of their hearing siblings. Most of these individuals had an onset of severe to profound hearing loss by early childhood. Marital rates of deaf adults were similar to their hearing siblings (0.83 vs. 0.85). Among married individuals, the fertility of deaf individuals is lower than their hearing siblings (2.06 vs. 2.26, p = 0.005). The fitness of deaf individuals was reduced (p = 0.002). Analysis of fertility rates after stratification by mating type reveals that matings between two deaf individuals produced more children (2.11) than matings of a deaf and hearing individual (1.85), suggesting that fertility among deaf individuals is influenced by multiple factors.

Provision of genetic services for hearing loss: results from a national survey and comparison to insights obtained from previous focus group discussions.

Hearing loss is a common sensory deficit and more than 50% of affected individuals have a genetic etiology. The discovery of 40 genes and more than 100 loci involved in hearing loss has made genetic testing for some of these genes widely available. Genetic services for deafness are also being sought more often due to the early identification of hearing loss through newborn screening services. The motivations for pursuing genetic testing, and how genetic services are provided to the client may differ among individuals. Additionally, information obtained through genetic testing can be perceived and used in different ways by parents of deaf children and deaf adults. This study aimed to follow up on focus group studies published earlier with a quantitative survey instrument and assess the preference of consumers for provision of genetic services. We conducted a national survey of hearing and deaf parents of children with hearing loss and of deaf adults. Data was compared and analyzed by hearing status of the participant, their community affiliation and the genetic testing status using nominal logistic regression. Consistent with our focus group results, the survey participants thought that a genetic counselor/geneticist would be the most appropriate professional to provide genetics services. Statistically significant differences were noted in the preferred choice of provider based on the genetic testing status. Parents preferred that genetic evaluation, including testing, occur either immediately at or a few months after the audiologic diagnosis of hearing loss. This data should help providers in clinical genetics keep patient preferences at the helm and provide culturally competent services.

Impact of genetic advances and testing for hearing loss: results from a national consumer survey.

Hearing loss is a common neuro-sensory deficit; nearly 50% of children with hearing loss have a genetic etiology. With the discovery of 40 genes and more than 100 loci involved in hearing loss, genetic testing is becoming more widely available. The information obtained through genetic testing can be perceived and used in different ways by parents of deaf children and deaf adults, based on their prior knowledge and understanding of these advances. It is therefore important to clarify the feelings of these potential consumers towards genetic services for hearing loss and understand their goals for genetic testing. The present study evaluates the feelings of consumers towards the advances in the genetics of hearing loss, the motivations for pursuing testing, and the perceived impact testing may have on their lives. We surveyed 808 parents of children with hearing loss nationally and 156 young deaf adults at Gallaudet University. In this study, learning the etiology of the hearing loss was the most commonly cited motivation for pursuing genetic testing and for parents was the most commonly cited outcome that genetic testing may have on their children's lives. Culturally Deaf respondents were less likely to believe that genetic testing will impact their lives or their children's lives and were less likely to report positive feelings about advances in the genetics of hearing loss. Cultural affiliation and genetic testing status, rather than hearing status, contributed more to the participants' responses.

Hypo-functional SLC26A4 variants associated with nonsyndromic hearing loss and enlargement of the vestibular aqueduct: genotype-phenotype correlation or coincidental polymorphisms?

Hearing loss with enlargement of the vestibular aqueduct (EVA) can be associated with mutations of the SLC26A4 gene encoding pendrin, a transmembrane Cl(-)/I(-)/HCO(3)(-) exchanger. Pendrin's critical transport substrates are thought to be I(-) in the thyroid gland and HCO(3)(-) in the inner ear. We previously reported that bi-allelic SLC26A4 mutations are associated with Pendred syndromic EVA whereas one or zero mutant alleles are associated with nonsyndromic EVA. One study proposed a correlation of nonsyndromic EVA with SLC26A4 alleles encoding pendrin with residual transport activity. Here we describe the phenotypes and SLC26A4 genotypes of 47 EVA patients ascertained since our first report of 39 patients. We sought to determine the pathogenic potential of each variant in our full cohort of 86 patients. We evaluated the trafficking of 11 missense pendrin products expressed in COS-7 cells. Products that targeted to the plasma membrane were expressed in Xenopus oocytes for measurement of anion exchange activity. p.F335L, p.C565Y, p.L597S, p.M775T, and p.R776C had Cl(-)/I(-) and Cl(-)/HCO(3)(-) exchange rate constants that ranged from 13 to 93% of wild type values. p.F335L, p.L597S, p.M775T and p.R776C are typically found as mono-allelic variants in nonsyndromic EVA. The high normal control carrier rate for p.L597S indicates it is a coincidentally detected nonpathogenic variant in this context. We observed moderate differential effects of hypo-functional variants upon exchange of HCO(3)(-) versus I(-) but their magnitude does not support a causal association with nonsyndromic EVA. However, these alleles could be pathogenic in trans configuration with a mutant allele in Pendred syndrome.

Phenotypic variability of patients homozygous for the GJB2 mutation 35delG cannot be explained by the influence of one major modifier gene.

Hereditary hearing loss (HL) is a very heterogeneous trait, with 46 gene identifications for non-syndromic HL. Mutations in GJB2 cause up to half of all cases of severe-to-profound congenital autosomal recessive non-syndromic HL, with 35delG being the most frequent mutation in Caucasians. Although a genotype-phenotype correlation has been established for most GJB2 genotypes, the HL of 35delG homozygous patients is mild to profound. We hypothesise that this phenotypic variability is at least partly caused by the influence of modifier genes. By performing a whole-genome association (WGA) study on 35delG homozygotes, we sought to identify modifier genes. The association study was performed by comparing the genotypes of mild/moderate cases and profound cases. The first analysis included a pooling-based WGA study of a first set of 255 samples by using both the Illumina 550K and Affymetrix 500K chips. This analysis resulted in a ranking of all analysed single-nucleotide polymorphisms (SNPs) according to their P-values. The top 250 most significantly associated SNPs were genotyped individually in the same sample set. All 192 SNPs that still had significant P-values were genotyped in a second independent set of 297 samples for replication. The significant P-values were replicated in nine SNPs, with combined P-values between 3 x 10(-3) and 1 x 10(-4). This study suggests that the phenotypic variability in 35delG homozygous patients cannot be explained by the effect of one major modifier gene. Significantly associated SNPs may reflect a small modifying effect on the phenotype. Increasing the power of the study will be of greatest importance to confirm these results.

A comparative analysis of the genetic epidemiology of deafness in the United States in two sets of pedigrees collected more than a century apart.

In 1898, E.A. Fay published an analysis of nearly 5000 marriages among deaf individuals in America collected during the 19(th) century. Each pedigree included three-generation data on marriage partners that included at least one deaf proband, who were ascertained by complete selection. We recently proposed that the intense phenotypic assortative mating among the deaf might have greatly accelerated the normally slow response to relaxed genetic selection against deafness that began in many Western countries with the introduction of sign language and the establishment of residential schools. Simulation studies suggest that this mechanism might have doubled the frequency of the commonest forms of recessive deafness (DFNB1) in this country during the past 200 years. To test this prediction, we collected pedigree data on 311 contemporary marriages among deaf individuals that were comparable to those collected by Fay. Segregation analysis of the resulting data revealed that the estimated proportion of noncomplementary matings that can produce only deaf children has increased by a factor of more than five in the past 100 years. Additional analysis within our sample of contemporary pedigrees showed that there was a statistically significant linear increase in the prevalence of pathologic GJB2 mutations when the data on 441 probands were partitioned into three 20-year birth cohorts (1920 through 1980). These data are consistent with the increase in the frequency of DFNB1 predicted by our previous simulation studies and provide convincing evidence for the important influence that assortative mating can have on the frequency of common genes for deafness.

Ethical and social implications of genetic testing for communication disorders.

UNLABELLED: Advances in genetics and genomics have quickly led to clinical applications to human health which have far-reaching consequences at the individual and societal levels. These new technologies have allowed a better understanding of the genetic factors involved in a wide range of disorders. During the past decade, incredible progress has been made in the identification of genes involved in the normal process of hearing. The resulting clinical applications have presented consumers with new information and choices. Many of the same gene identification techniques are increasingly being applied to the investigation of complex disorders of speech and language. In parallel with gene identification, studies of the legal, ethical and psychosocial impacts of the clinical application of these advances and their influence on specific behaviors of individuals with communication disorders are paramount, but often lag behind. These studies will help to ensure that new technologies are introduced into clinical practice in a responsible manner. LEARNING OUTCOMES: As a result of this activity, the participant will be able to (1) explain the differences between Mendelian and complex forms of inheritance and why these differences complicate the ethical impact of genetic testing, (2) explain how publicly funded genome research through the Human Genome Project, the International HapMap Project and others have examined the ethical, legal and social implications of genome research, (3) list some of the ethical complexities of prenatal, newborn and predictive testing for various genetic disorders and (4) discuss the importance of evidence-based practice to the development of public policy for the introduction and clinical use of genetic tests.

Consumer motivations for pursuing genetic testing and their preferences for the provision of genetic services for hearing loss.

Genetic services for deafness are being increasingly sought due to the introduction of early hearing detection and intervention programs, as well as the rapid progress in the identification of deafness genes. This study aimed to assess the motivations of consumers for pursuing genetic testing as well as their preferences for provision of these services. We conducted 5 focus groups consisting of hearing parents of deaf children, deaf parents, and unmarried deaf adults. Motivations for pursuing genetic testing included determining the etiology, helping to alleviate the guilt associated with the diagnosis of hearing loss in a child, and acquiring information to help them and other family members prepare for the future. Most participants thought that a genetic counselor/geneticist would be the most appropriate professional to provide genetics services. For culturally Deaf individuals, the communication method was seen as more important than the type of professional. Parents preferred that genetic evaluation, including testing, occur either immediately at or a few months after the audiologic diagnosis of hearing loss.

Compound heterozygosity for dominant and recessive GJB2 mutations: effect on phenotype and review of the literature.

Mutations in GJB2 (which encodes the gap-junction protein connexin 26) are the most common cause of genetic deafness in many populations. To date, more than 100 deafness-causing mutations have been described in this gene. The majority of these mutations are inherited in an autosomal recessive manner, but approximately 19 GJB2 mutations have been associated with dominantly inherited hearing loss. One, W44C, was first identified in two families from France. We subsequently described a family in the United States with the same mutation. In these families, W44C segregates with a dominantly inherited, early-onset, progressive, sensorineural deafness that is worse in the high frequencies. Since that report, we have tested additional family members and identified two siblings who are compound heterozygous for the W44C and K15T mutations. Their father, the original proband, is heterozygous for the dominant W44C mutation, and their mother is compound heterozygous for two recessively inherited mutations, K15T and 35delG. Both children have a profound, sensorineural deafness and use manual communication, in contrast to their parents and other relatives whose hearing losses are less severe and who can communicate orally. The difference in phenotype may be a result of the disruption of different functions of the gap-junction protein by the two mutations, which have an additive effect.