A gene for autosomal dominant nonsyndromic hearing loss (DFNA12) maps to chromosome 11q22-24.

We performed linkage analysis in a Belgian family with autosomal dominant midfrequency hearing loss, which has a prelingual onset and a nonprogressive course in most patients. We found LOD scores >6 with markers on chromosome 11q. Analysis of key recombinants maps this deafness gene (DFNA12) to a 36-cM interval on chromosome 11q22-24, between markers D11S4120 and D11S912. The critical regions for the recessive deafness locus DFNB2 and the dominant locus DFNA11, which were previously localized to the long arm of chromosome 11, do not overlap with the candidate interval of DFNA12.     

Genetic and molecular analysis of the CLDN14 gene in Moroccan family with non-syndromic hearing loss

BACKGROUND:

Hearing loss is the most prevalent human genetic sensorineural defect. Mutations in the CLDN14 gene, encoding the tight junction claudin 14 protein expressed in the inner ear, have been shown to cause non-syndromic recessive hearing loss DFNB29.

AIM:

We describe a Moroccan SF7 family with non-syndromic hearing loss. We performed linkage analysis in this family and sequencing to identify the mutation causing deafness.

MATERIALS AND METHODS:

Genetic linkage analysis, suggested the involvement of CLDN14 and KCNE1 gene in deafness in this family. Mutation screening was performed using direct sequencing of the CLDN14 and KCNE1 coding exon gene.

RESULTS:

Our results show the presence of c.11C>T mutation in the CLDN14 gene. Transmission analysis of this mutation in the family showed that the three affected individuals are homozygous, whereas parents and three healthy individuals are heterozygous. This mutation induces a substitution of threonine to methionine at position 4.

CONCLUSION:

These data show that CLDN14 gene can be i mplicated in the development of hearing loss in SF7 family; however, the pathogenicity of c.11C>T mutation remains to be determined.     

Temperature-sensitive auditory neuropathy associated with an otoferlin mutation: Deafening fever!

Transient deafness associated with an increase in core body temperature is a rare and puzzling disorder. Temperature-dependent deafness has been previously observed in patients suffering from auditory neuropathy. Auditory neuropathy is a clinical entity of sensorineural deafness characterized by absent auditory brainstem response and normal otoacoustic emissions. Mutations in OTOF, which encodes otoferlin, have been previously reported to cause DFNB9, a non-syndromic form of deafness characterized by severe to profound prelingual hearing impairment and auditory neuropathy.Here we report a novel mutation in OTOF gene in a large family affected by temperature-dependent auditory neuropathy. Three siblings aged 10, 9 and 7 years from a consanguineous family were found to be affected by severe or profound hearing impairment that was only present when they were febrile. The non-febrile patients had only mild if any hearing impairment. Electrophysiological tests revealed auditory neuropathy. Mapping with microsatellite markers revealed a compatible linkage in the DFNB9/OTOF region in the family, prompting us to run a molecular analysis of the 48 exons and of the OTOF intron-exon boundaries. This study revealed a novel mutation p.Glu1804del in exon 44 of OTOF. The mutation was found to be homozygous in the three patients and segregated with the hearing impairment within the family. The deletion affects an amino acid that is conserved in mammalian otoferlin sequences and located in the calcium-binding domain C2F of the protein.     

Autosomal recessive nonsyndromic deafness locus DFNB63 at chromosome 11q13.2–q13.3

A genome wide linkage analysis of nonsyndromic deafness segregating in a consanguineous Pakistani family (PKDF537) was used to identify DFNB63, a new locus for congenital profound sensorineural hearing loss. A maximum two-point lod score of 6.98 at θ = 0 was obtained for marker D11S1337 (68.55 cM). Genotyping of 550 families revealed three additional families (PKDF295, PKDF702 and PKDF817) segregating hearing loss linked to chromosome 11q13.2-q13.3. Meiotic recombination events in these four families define a critical interval of 4.81 cM bounded by markers D11S4113 (68.01 cM) and D11S4162 (72.82 cM), and SHANK2, FGF-3, TPCN2 and CTTN are among the candidate genes in this interval. Positional identification of this deafness gene should reveal a protein necessary for normal development and/or function of the auditory system.     

Identification of a Novel TECTA Mutation in a Chinese DFNA8/12 Family with Prelingual Progressive Sensorineural Hearing Impairment

Tectorial membrane, an extracellular matrix of the cochlea, plays a crucial role in the transmission of sound to the sensory hair cells. Alpha-tectorin is the most important noncollagenous component of the tectorial membrane and the otolith membrane in the maculae of the vestibular system. Defects in TECTA, the gene encodes alpha-tectorin, are cause of both dominant (DFNA8/12) and recessive (DFNB21) forms of deafness. Here, we report a three-generation Chinese family characterized by prelingual progressive sensorineural hearing impairment. We mapped the disease locus to chromosome 11q23-24 region, overlapping with the DFNA8/12 locus. Sequencing of candidate gene TECTA revealed a heterozygous c.5945C>A substitution in exon 19, causing amino acid substitution of Ala to Asp at a conservative position 1982. The A1982D substitution is consistent with hearing loss in this Chinese family and has not been found in 200 random control chromosomes. To our knowledge, this is the first TECTA mutation identified in Chinese population. Our data provides additional molecular and clinical information for establishing a better genotype–phenotype understanding of DFNA8/12.     

Novel mutations in the connexin 26 gene (GJB2) that cause autosomal recessive (DFNB1) hearing loss.

Mutations in the connexin 26 (Cx26) gene (GJB2) are associated with the type of autosomal recessive nonsyndromic neurosensory deafness known as "DFNB1." Studies indicate that DFNB1 (13q11-12) causes 20% of all childhood deafness and may have a carrier rate as high as 2. 8%. This study describes the analysis of 58 multiplex families each having at least two affected children diagnosed with autosomal recessive nonsyndromic deafness. Twenty of the 58 families were observed to have mutations in both alleles of Cx26. Thirty-three of 116 chromosomes contained a 30delG allele, for a frequency of .284. This mutation was observed in 2 of 192 control chromosomes, for an estimated gene frequency of .01+/-.007. The homozygous frequency of the 30delG allele is then estimated at .0001, or 1/10,000. Given that the frequency of all childhood hearing impairment is 1/1,000 and that half of that is genetic, the specific mutation 30delG is responsible for 10% of all childhood hearing loss and for 20% of all childhood hereditary hearing loss. Six novel mutations were also observed in the affected population. The deletions detected cause frameshifts that would severely disrupt the protein structure. Three novel missense mutations, Val84Met, Val95Met, and Ser113Pro, were observed. The missense mutation 101T-->C has been reported to be a dominant allele of DFNA3, a dominant nonsyndromic hearing loss. Data further supporting the finding that this mutation does not cause dominant hearing loss are presented. This allele was found in a recessive family segregating independently from the hearing-loss phenotype and in 3 of 192 control chromosomes. These results indicate that 101T-->C is not sufficient to cause hearing loss.     

Mutations in TBC1D24, a Gene Associated With Epilepsy,Also Cause Nonsyndromic Deafness DFNB86

Inherited deafness is clinically and genetically heterogeneous. We recently mapped DFNB86, a locus associated with nonsyndromic deafness, to chromosome 16p. In this study, whole-exome sequencing was performed with genomic DNA from affected individuals from three large consanguineous families in which markers linked to DFNB86 segregate with profound deafness. Analyses of these data revealed homozygous mutation c.208G>T (p.Asp70Tyr) or c.878G>C (p.Arg293Pro) in TBC1D24 as the underlying cause of deafness in the three families. Sanger sequence analysis of TBC1D24 in an additional large family in which deafness segregates with DFNB86 identified the c.208G>T (p.Asp70Tyr) substitution. These mutations affect TBC1D24 amino acid residues that are conserved in orthologs ranging from fruit fly to human. Neither variant was observed in databases of single-nucleotide variants or in 634 chromosomes from ethnically matched control subjects. TBC1D24 in the mouse inner ear was immunolocalized predominantly to spiral ganglion neurons, indicating that DFNB86 deafness might be an auditory neuropathy spectrum disorder. Previously, six recessive mutations in TBC1D24 were reported to cause seizures (hearing loss was not reported) ranging in severity from epilepsy with otherwise normal development to epileptic encephalopathy resulting in childhood death. Two of our four families in which deafness segregates with mutant alleles of TBC1D24 were available for neurological examination. Cosegregation of epilepsy and deafness was not observed in these two families. Although the causal relationship between genotype and phenotype is not presently understood, our findings, combined with published data, indicate that recessive alleles of TBC1D24 can cause either epilepsy or nonsyndromic deafness.     

An autosomal recessive nonsyndromic-hearing-loss locus identified by DNA pooling using two inbred Bedouin kindreds.

Autosomal recessive nonsyndromic hearing loss (ARNSHL) is the most common form of severe inherited childhood deafness. We present the linkage analysis of two inbred Bedouin kindreds from Israel that are affected with ARNSHL. A rapid genomewide screen for markers linked to the disease was performed by using pooled DNA samples. This screen revealed evidence for linkage with markers D9S922 and D9S301 on chromosome 9q. Genotyping of individuals from both kindreds confirmed linkage to chromosome 9q and a maximum combined LOD score of 26.2 (recombination fraction [theta] .025) with marker D9S927. The disease locus was mapped to a 1.6-cM region of chromosome 9ql3-q2l, between markers D9S15 and D9S927. The disease segregates with a common haplotype in the two kindreds, at markers D9S927, D9S175, and D9S284 in the linked interval, supporting the hypothesis that both kindreds inherited the deafness gene from a common ancestor. Although this nonsyndromic-hearing-loss (NSHL) locus maps to the same cytogenetic interval as DFNB7, it does not overlap the currently defined DFNB7 interval and may represent (1) a novel form of NSHL in close proximity to DFNB7 or (2) a relocalization of the DFNB7 interval to a region telomeric to its reported location. This study further demonstrates that DNA pooling is an effective means of quickly identifying regions of linkage in inbred families with heterogeneous autosomal recessive disorders.     

Mutations of GIPC3 cause nonsyndromic hearing loss DFNB72 but not DFNB81 that also maps to chromosome 19p

A missense mutation of Gipc3 was previously reported to cause age-related hearing loss in mice. Point mutations of human GIPC3 were found in two small families, but association with hearing loss was not statistically significant. Here, we describe one frameshift and six missense mutations in GIPC3 cosegregating with DFNB72 hearing loss in six large families that support statistically significant evidence for genetic linkage. However, GIPC3 is not the only nonsyndromic hearing impairment gene in this region; no GIPC3 mutations were found in a family cosegregating hearing loss with markers of chromosome 19p. Haplotype analysis excluded GIPC3 from the obligate linkage interval in this family and defined a novel locus spanning 4.08?Mb and 104 genes. This closely linked but distinct nonsyndromic hearing loss locus was designated DFNB81.     

Mutations of the Gene Encoding Otogelin Are a Cause of Autosomal-Recessive Nonsyndromic Moderate Hearing Impairment

Already 40 genes have been identified for autosomal-recessive nonsyndromic hearing impairment (arNSHI); however, many more genes are still to be identified. In a Dutch family segregating arNSHI, homozygosity mapping revealed a 2.4 Mb homozygous region on chromosome 11 in p15.1-15.2, which partially overlapped with the previously described DFNB18 locus. However, no putative pathogenic variants were found in USH1C, the gene mutated in DFNB18 hearing impairment. The homozygous region contained 12 additional annotated genes including OTOG, the gene encoding otogelin, a component of the tectorial membrane. It is thought that otogelin contributes to the stability and strength of this membrane through interaction or stabilization of its constituent fibers. The murine orthologous gene was already known to cause hearing loss when defective. Analysis of OTOG in the Dutch family revealed a homozygous 1 bp deletion, c.5508delC, which leads to a shift in the reading frame and a premature stop codon, p.Ala1838ProfsX31. Further screening of 60 unrelated probands from Spanish arNSHI families detected compound heterozygous OTOG mutations in one family, c.6347C>T (p.Pro2116Leu) and c. 6559C>T (p.Arg2187X). The missense mutation p.Pro2116Leu affects a highly conserved residue in the fourth von Willebrand factor type D domain of otogelin. The subjects with OTOG mutations have a moderate hearing impairment, which can be associated with vestibular dysfunction. The flat to shallow “U” or slightly downsloping shaped audiograms closely resembled audiograms of individuals with recessive mutations in the gene encoding α-tectorin, another component of the tectorial membrane. This distinctive phenotype may represent a clue to orientate the molecular diagnosis.     

Mutations of MYO6 are associated with recessive deafness,DFNB37

Cosegregation of profound, congenital deafness with markers on chromosome 6q13 in three Pakistani families defines a new recessive deafness locus, DFNB37. Haplotype analyses reveal a 6-cM linkage region, flanked by markers D6S1282 and D6S1031, that includes the gene encoding unconventional myosin VI. In families with recessively inherited deafness, DFNB37, our sequence analyses of MYO6 reveal a frameshift mutation (36-37insT), a nonsense mutation (R1166X), and a missense mutation (E216V). These mutations, along with a previously published missense allele linked to autosomal dominant progressive hearing loss (DFNA22), provide an allelic spectrum that probes the relationship between myosin VI dysfunction and the resulting phenotype.     

A genome-wide search for genes predisposing to manic-depression, assuming autosomal dominant inheritance.

Manic-depressive illness (MDI), also known as "bipolar affective disorder," is a common and devastating neuropsychiatric illness. Although pivotal biochemical alterations underlying the disease are unknown, results of family, twin, and adoption studies consistently implicate genetic transmission in the pathogenesis of MDI. In order to carry out linkage analysis, we ascertained eight moderately sized pedigrees containing multiple cases of the disease. For a four-allele marker mapping 5 cM from the disease gene, the pedigree sample has > 97% power to detect a dominant allele under genetic homogeneity and has > 73% power under 20% heterogeneity. To date, the eight pedigrees have been genotyped with 328 polymorphic DNA loci throughout the genome. When autosomal dominant inheritance was assumed, 273 DNA markers gave lod scores < -2.0 at recombination fraction (theta) = .0, 174 DNA loci produced lod scores < -2.0 at theta = .05, and 4 DNA marker loci yielded lod scores > 1 (chromosome 5--D5S39, D5S43, and D5S62; chromosome 11--D11S85). Of the markers giving lod scores > 1, only D5S62 continued to show evidence for linkage when the affected-pedigree-member method was used. The D5S62 locus maps to distal 5q, a region containing neurotransmitter-receptor genes for dopamine, norepinephrine, glutamate, and gamma-aminobutyric acid. Although additional work in this region may be warranted, our linkage results should be interpreted as preliminary data, as 68 unaffected individuals are not past the age of risk.     

Genetic mapping refines DFNB3 to 17p11.2, suggests multiple alleles of DFNB3, and supports homology to the mouse model shaker-2.

The nonsyndromic congenital recessive deafness gene, DFNB3, first identified in Bengkala, Bali, was mapped to a approximately 12-cM interval on chromosome 17. New short tandem repeats (STRs) and additional DNA samples were used to identify recombinants that constrain the DFNB3 interval to less, similar6 cM on 17p11.2. Affected individuals from Bengkala and affected members of a family with hereditary deafness who were from Bila, a village neighboring Bengkala, were homozygous for the same alleles for six adjacent STRs in the DFNB3 region and were heterozygous for other distal markers, thus limiting DFNB3 to an approximately 3-cM interval. Nonsyndromic deafness segregating in two unrelated consanguineous Indian families, M21 and I-1924, were also linked to the DFNB3 region. Haplotype analysis indicates that the DFNB3 mutations in the three pedigrees most likely arose independently and suggests that DFNB3 makes a significant contribution to hereditary deafness worldwide. On the basis of conserved synteny, mouse deafness mutations shaker-2 (sh2) and sh2J are proposed as models of DFNB3. Genetic mapping has refined sh2 to a 0.6-cM interval of chromosome 11. Three homologous genes map within the sh2 and DFNB3 intervals, suggesting that sh2 is the homologue of DFNB3.     

A unique point mutation in the PMP22 gene is associated with Charcot-Marie-Tooth disease and deafness.

Charcot-Marie-Tooth disease (CMT) with deafness is clinically distinct among the genetically heterogeneous group of CMT disorders. Molecular studies in a large family with autosomal dominant CMT and deafness have not been reported. The present molecular study involves a family with progressive features of CMT and deafness, originally reported by Kousseff et al. Genetic analysis of 70 individuals (31 affected, 28 unaffected, and 11 spouses) revealed linkage to markers on chromosome 17p11.2-p12, with a maximum LOD score of 9.01 for marker D17S1357 at a recombination fraction of .03. Haplotype analysis placed the CMT-deafness locus between markers D17S839 and D17S122, a approximately 0.6-Mb interval. This critical region lies within the CMT type 1A duplication region and excludes MYO15, a gene coding an unconventional myosin that causes a form of autosomal recessive deafness called DFNB3. Affected individuals from this family do not have the common 1.5-Mb duplication of CMT type 1A. Direct sequencing of the candidate peripheral myelin protein 22 (PMP22) gene detected a unique G-->C transversion in the heterozygous state in all affected individuals, at position 248 in coding exon 3, predicted to result in an Ala67Pro substitution in the second transmembrane domain of PMP22.     

A gene for universal congenital alopecia maps to chromosome 8p21-22.

Complete or partial congenital absence of hair (congenital alopecia) may occur either in isolation or with associated defects. The majority of families with isolated congenital alopecia has been reported to follow an autosomal-recessive mode of inheritance (MIM 203655). As yet, no gene has been linked to isolated congenital alopecia, nor has linkage been established to a specific region of the genome. In an attempt to map the gene for the autosomal recessive form of the disorder, we have performed genetic linkage analysis on a large inbred Pakistani family in which affected persons show complete absence of hair development (universal congenital alopecia). We have analyzed individuals of this family, using >175 microsatellite polymorphic markers of the human genome. A maximum LOD score of 7.90 at a recombination fraction of 0 has been obtained with locus D8S258. Haplotype analysis of recombination events localized the disease to a 15-cM region between marker loci D8S261 and D8S1771. We have thus mapped the gene for this hereditary form of isolated congenital alopecia to a locus on chromosome 8p21-22 (ALUNC [alopecia universalis congenitalis]). This will aid future identification of the responsible gene, which will be extremely useful for the understanding of the biochemistry of hair development.     

Exome Sequencing Identifies a Mutation in EYA4 as a Novel Cause of Autosomal Dominant Non-Syndromic Hearing Loss

Autosomal dominant non-syndromic hearing loss is highly heterogeneous, and eyes absent 4 (EYA4) is a disease-causing gene. Most EYA4 mutations founded in the Eya-homologous region, however, no deafness causative missense mutation in variable region of EYA4 have previously been found. In this study, we identified a pathogenic missense mutation located in the variable region of the EYA4 gene for the first time in a four-generation Chinese family with 57 members. Whole-exome sequencing (WES) was performed on samples from one unaffected and two affected individuals to systematically search for deafness susceptibility genes, and the candidate mutations and the co-segregation of the phenotype were verified by polymerase chain reaction amplification and by Sanger sequencing in all of the family members. Then, we identified a novel EYA4 mutation in exon 8, c.511G>C; p.G171R, which segregated with postlingual and progressive autosomal dominant sensorineural hearing loss (SNHL). This report is the first to describe a missense mutation in the variable region domain of the EYA4 gene, which is not highly conserved in many species, indicating that the potential unconserved role of 171G>R in human EYA4 function is extremely important.     

Recessive TBC1D24 Mutations Are Frequent in Moroccan Non-Syndromic Hearing Loss Pedigrees

Mutations in the TBC1D24 gene are responsible for four neurological presentations: infantile epileptic encephalopathy, infantile myoclonic epilepsy, DOORS (deafness, onychodystrophy, osteodystrophy, mental retardation and seizures) and NSHL (non-syndromic hearing loss). For the latter, two recessive (DFNB86) and one dominant (DFNA65) mutations have so far been identified in consanguineous Pakistani and European/Chinese families, respectively. Here we report the results of a genetic study performed on a large Moroccan cohort of deaf patients that identified three families with compound heterozygote mutations in TBC1D24. Four novel mutations were identified, among which, one c.641G>A (p.Arg214His) was present in the three families, and has a frequency of 2% in control Moroccan population with normal hearing, suggesting that it acts as an hypomorphic variant leading to restricted deafness when combined with another recessive severe mutation. Altogether, our results show that mutations in TBC1D24 gene are a frequent cause (>2%) of NSHL in Morocco, and that due to its possible compound heterozygote recessive transmission, this gene should be further considered and screened in other deaf cohorts.