Mutation of the ATP-gated P2X(2) receptor leads to progressive hearing loss and increased susceptibility to noise.

Age-related hearing loss and noise-induced hearing loss are major causes of human morbidity. Here we used genetics and functional studies to show that a shared cause of these disorders may be loss of function of the ATP-gated P2X(2) receptor (ligand-gated ion channel, purinergic receptor 2) that is expressed in sensory and supporting cells of the cochlea. Genomic analysis of dominantly inherited, progressive sensorineural hearing loss DFNA41 in a six-generation kindred revealed a rare heterozygous allele, P2RX2 c.178G > T (p.V60L), at chr12:133,196,029, which cosegregated with fully penetrant hearing loss in the index family, and also appeared in a second family with the same phenotype. The mutation was absent from more than 7,000 controls. P2RX2 p.V60L abolishes two hallmark features of P2X(2) receptors: ATP-evoked inward current response and ATP-stimulated macropore permeability, measured as loss of ATP-activated FM1-43 fluorescence labeling. Coexpression of mutant and WT P2X(2) receptor subunits significantly reduced ATP-activated membrane permeability. P2RX2-null mice developed severe progressive hearing loss, and their early exposure to continuous moderate noise led to high-frequency hearing loss as young adults. Similarly, among family members heterozygous for P2RX2 p.V60L, noise exposure exacerbated high-frequency hearing loss in young adulthood. Our results suggest that P2X(2) function is required for life-long normal hearing and for protection from exposure to noise.

Mutations in OTOGL, encoding the inner ear protein otogelin-like, cause moderate sensorineural hearing loss.

Hereditary hearing loss is characterized by a high degree of genetic heterogeneity. Here we present OTOGL mutations, a homozygous one base pair deletion (c.1430 delT) causing a frameshift (p.Val477Glufs(∗)25) in a large consanguineous family and two compound heterozygous mutations, c.547C>T (p.Arg183(∗)) and c.5238+5G>A, in a nonconsanguineous family with moderate nonsyndromic sensorineural hearing loss. OTOGL maps to the DFNB84 locus at 12q21.31 and encodes otogelin-like, which has structural similarities to the epithelial-secreted mucin protein family. We demonstrate that Otogl is expressed in the inner ear of vertebrates with a transcription level that is high in embryonic, lower in neonatal, and much lower in adult stages. Otogelin-like is localized to the acellular membranes of the cochlea and the vestibular system and to a variety of inner ear cells located underneath these membranes. Knocking down of otogl with morpholinos in zebrafish leads to sensorineural hearing loss and anatomical changes in the inner ear, supporting that otogelin-like is essential for normal inner ear function. We propose that OTOGL mutations affect the production and/or function of acellular structures of the inner ear, which ultimately leads to sensorineural hearing loss.

Mutations in ANKRD11 cause KBG syndrome, characterized by intellectual disability, skeletal malformations, and macrodontia.

KBG syndrome is characterized by intellectual disability associated with macrodontia of the upper central incisors as well as distinct craniofacial findings, short stature, and skeletal anomalies. Although believed to be genetic in origin, the specific underlying defect is unknown. Through whole-exome sequencing, we identified deleterious heterozygous mutations in ANKRD11 encoding ankyrin repeat domain 11, also known as ankyrin repeat-containing cofactor 1. A splice-site mutation, c.7570-1G>C (p.Glu2524_Lys2525del), cosegregated with the disease in a family with three affected members, whereas in a simplex case a de novo truncating mutation, c.2305delT (p.Ser769GlnfsX8), was detected. Sanger sequencing revealed additional de novo truncating ANKRD11 mutations in three other simplex cases. ANKRD11 is known to interact with nuclear receptor complexes to modify transcriptional activation. We demonstrated that ANKRD11 localizes mainly to the nuclei of neurons and accumulates in discrete inclusions when neurons are depolarized, suggesting that it plays a role in neural plasticity. Our results demonstrate that mutations in ANKRD11 cause KBG syndrome and outline a fundamental role of ANKRD11 in craniofacial, dental, skeletal, and central nervous system development and function.

MASP1 mutations in patients with facial, umbilical, coccygeal, and auditory findings of Carnevale, Malpuech, OSA, and Michels syndromes.

Distinctive facial features consisting of hypertelorism, telecanthus, blepharophimosis, blepharoptosis, epicanthus inversus, periumbilical defects, and skeletal anomalies are seen in autosomal-recessive Carnevale, Malpuech, Michels, and oculo-skeletal-abdominal (OSA) syndromes. The gene or genes responsible for these syndromes were heretofore unknown. We report on three individuals from two consanguineous Turkish families with findings characteristic of these syndromes, including facial dysmorphism, periumbilical depression, mixed hearing loss, radioulnar synostosis, and coccygeal appendage. Homozygosity mapping yielded an autozygous region on chromosome 3q27 in both families. In one family, whole exome sequencing revealed a missense mutation, MASP1 c.2059G>A (p.G687R), that cosegregated with the phenotype. In the second family, Sanger sequencing of MASP1 revealed a nonsense mutation, MASP1 c.870G>A (p.W290X), that also cosegregated with the phenotype. Neither mutation was found in 192 Turkish controls or 1200 controls of various other ancestries. MASP1 encodes mannan-binding lectin serine protease 1. The two mutations occur in a MASP1 isoform that has been reported to process IGFBP-5, thereby playing a critical role in insulin growth factor availability during craniofacial and muscle development. These results implicate mutations of MASP1 as the cause of a human malformation syndrome and demonstrate the involvement of MASP1 in facial, umbilical, and ear development during the embryonic period.

A truncating mutation in SERPINB6 is associated with autosomal-recessive nonsyndromic sensorineural hearing loss.

More than 270 million people worldwide have hearing loss that affects normal communication. Although astonishing progress has been made in the identification of more than 50 genes for deafness during the past decade, the majority of deafness genes are yet to be identified. In this study, we mapped a previously unknown autosomal-recessive nonsyndromic sensorineural hearing loss locus (DFNB91) to chromosome 6p25 in a consanguineous Turkish family. The degree of hearing loss was moderate to severe in affected individuals. We subsequently identified a nonsense mutation (p.E245X) in SERPINB6, which is located within the linkage interval for DFNB91 and encodes for an intracellular protease inhibitor. The p.E245X mutation cosegregated in the family as a completely penetrant autosomal-recessive trait and was absent in 300 Turkish controls. The mRNA expression of SERPINB6 was reduced and production of protein was absent in the peripheral leukocytes of homozygotes, suggesting that the hearing loss is due to loss of function of SERPINB6. We also demonstrated that SERPINB6 was expressed primarily in the inner ear hair cells. We propose that SERPINB6 plays an important role in the inner ear in the protection against leakage of lysosomal content during stress and that loss of this protection results in cell death and sensorineural hearing loss.

A complex TFAP2A allele is associated with branchio-oculo-facial syndrome and inner ear malformation in a deaf child.

We present a 4-year-old girl with congenital profound sensorineural deafness associated with inner ear malformation (incomplete partition type II, enlarged vestibule, and enlarged vestibular aqueduct). The proposita also had pseudocleft lips, skin defects, auricle abnormalities, and unilateral multicystic dysplastic kidney, leading to the diagnosis of branchio-oculo-facial (BOF) syndrome. Mutation analysis of the TFAP2A gene showed a de novo deletion of 18 and insertion of 6 nucleotides, resulting in deletion of amino acids LPGARR and insertion of RI between amino acids 276 and 281. Altered amino acids are located within the basic DNA binding and dimerization domains of TFAP2A. Previously reported amino acid substitutions in TFAP2A involved only DNA binding domain in four patients with BOF syndrome who were not reported to have profound sensorineural deafness. Our report implies that the localization of mutations in TFAP2A might be responsible with the phenotypic findings in BOF syndrome.

Homozygous mutations in the 15-hydroxyprostaglandin dehydrogenase gene in patients with primary hypertrophic osteoarthropathy.

Mutations in HPGD have recently been reported to cause primary hypertrophic osteoarthropathy (PHO), a rare genetic disease characterized by digital clubbing, pachydermia, and periostosis. We screened HPGD mutations in six patients from three unrelated Turkish families with PHO, in which we showed one previously reported, p.A140P, and one novel, p.M1L, homozygous mutations. Both mutations co-segregated with the phenotype in all three families and were absent in 100 Turkish controls. These results confirm the presence of biallelic HPGD mutations in patients with PHO in an independent series from a different population.

Research of genetic bases of hereditary non-syndromic hearing loss.

AIM: Hearing loss is the most common sensory disorder that affects approximately one per 1000 live births. With this project, we aimed to identify gene variants that were common causes of hearing loss in Turkey to contribute to the planning of genetic screening programs for hearing loss, as well as to improve genetic counseling to affected families. MATERIAL AND METHODS: Twenty-one families with at least two affected individuals and parental consanguinity who presented with non-syndromic severe-to-profound sensorineural hearing loss were included in this study. We first screened for mutations in GJB2 and mitochondrial DNA 12S RNA genes. Subsequently, we genotyped the TMIE c.250C>T and SNP markers flanking the SLC26A4, MYO7A, MYO15A, OTOF, CDH23, TMIE, TECTA, PCDH15, TMC1, TMPRSS3, TMHS genes in the remaining twelve families without mutations in GJB2. RESULTS: Screening for mutations in GJB2 gene showed c.[35delG];[35delG] mutation in four families, c.[35delG];[507C>A] mutation in two families, c.[35delG];[-23+1G>A] mutation in one family, and c.457G>A heterozygous mutation in one family. Genotyping SNP markers showed the c.[250C>T];[250C>T] mutation in TMIE in one family. A homozygous region with SNP genotypes was detected with the OTOF gene in one family, the TMPRSS3 gene in another family, and also a homozygous region was detected with TMHS, OTOF, and TMPRSS3 genes in another family. CONCLUSIONS: Further research will be required to determine the genetic bases of hearing loss in families with non-syndromic hearing loss.

Challenges in whole exome sequencing: an example from hereditary deafness.

Whole exome sequencing provides unprecedented opportunities to identify causative DNA variants in rare Mendelian disorders. Finding the responsible mutation via traditional methods in families with hearing loss is difficult due to a high degree of genetic heterogeneity. In this study we combined autozygosity mapping and whole exome sequencing in a family with 3 affected children having nonsyndromic hearing loss born to consanguineous parents. Two novel missense homozygous variants, c.508C>A (p.H170N) in GIPC3 and c.1328C>T (p.T443M) in ZNF57, were identified in the same ∼6 Mb autozygous region on chromosome 19 in affected members of the family. Both variants co-segregated with the phenotype and were absent in 335 ethnicity-matched controls. Biallelic GIPC3 mutations have recently been reported to cause autosomal recessive nonsyndromic sensorineural hearing loss. Thus we conclude that the hearing loss in the family described in this report is caused by a novel missense mutation in GIPC3. Identified variant in GIPC3 had a low read depth, which was initially filtered out during the analysis leaving ZNF57 as the only potential causative gene. This study highlights some of the challenges in the analyses of whole exome data in the bid to establish the true causative variant in Mendelian disease.

Whole-exome sequencing efficiently detects rare mutations in autosomal recessive nonsyndromic hearing loss.

Identification of the pathogenic mutations underlying autosomal recessive nonsyndromic hearing loss (ARNSHL) is difficult, since causative mutations in 39 different genes have so far been reported. After excluding mutations in the most common ARNSHL gene, GJB2, via Sanger sequencing, we performed whole-exome sequencing (WES) in 30 individuals from 20 unrelated multiplex consanguineous families with ARNSHL. Agilent SureSelect Human All Exon 50 Mb kits and an Illumina Hiseq2000 instrument were used. An average of 93%, 84% and 73% of bases were covered to 1X, 10X and 20X within the ARNSHL-related coding RefSeq exons, respectively. Uncovered regions with WES included those that are not targeted by the exome capture kit and regions with high GC content. Twelve homozygous mutations in known deafness genes, of which eight are novel, were identified in 12 families: MYO15A-p.Q1425X, -p.S1481P, -p.A1551D; LOXHD1-p.R1494X, -p.E955X; GIPC3-p.H170N; ILDR1-p.Q274X; MYO7A-p.G2163S; TECTA-p.Y1737C; TMC1-p.S530X; TMPRSS3-p.F13Lfs*10; TRIOBP-p.R785Sfs*50. Each mutation was within a homozygous run documented via WES. Sanger sequencing confirmed co-segregation of the mutation with deafness in each family. Four rare heterozygous variants, predicted to be pathogenic, in known deafness genes were detected in 12 families where homozygous causative variants were already identified. Six heterozygous variants that had similar characteristics to those abovementioned variants were present in 15 ethnically-matched individuals with normal hearing. Our results show that rare causative mutations in known ARNSHL genes can be reliably identified via WES. The excess of heterozygous variants should be considered during search for causative mutations in ARNSHL genes, especially in small-sized families.

Unique spectrum of GJB2 mutations in Mexico.

OBJECTIVE: The aim of this study was to elucidate the involvement of mutations in three relatively common deafness genes in Mexican individuals with non-syndromic hearing loss. METHODS: We sequenced GJB2 for mutations, screened for two deletions involving GJB6, del(GJB6-D13S1830) and del(GJB6-D13S1854), and for the m.1555A>G mutation in the MTRNR1 gene in 76 (71 simplex and 5 multiplex) unrelated Mexican probands with prelingual non-syndromic hearing loss. Samples were obtained from the Department of Genetics at Instituto Nacional de Rehabilitacion in Mexico City. RESULTS: Eight previously reported pathogenic variants and two polymorphic variants in GJB2 were identified. The two screened GJB6 deletions and the m.1555A>G mutation were not detected. Eight cases (10.6%) were found to have bi-allelic mutations in GJB2 and six (7.9%) were found to have a monoallelic GJB2 mutation. Of the six monoallelic mutations, one (p.R184Q) was a previously reported autosomal dominant variant. The most frequent pathological allele detected in this population was the c.35delG mutation in the GJB2 gene. The p.V27I polymorphic variant was also detected, with an allele frequency of 0.24. All eight probands with GJB2 mutations had symmetric profound deafness, whereas patients without GJB2 mutations had moderate, severe or profound hearing loss. CONCLUSIONS: This study shows that GJB2 mutations are an important cause of prelingual deafness in the Mexican population.

Alterations of the CIB2 calcium- and integrin-binding protein cause Usher syndrome type 1J and nonsyndromic deafness DFNB48.

Sensorineural hearing loss is genetically heterogeneous. Here, we report that mutations in CIB2, which encodes a calcium- and integrin-binding protein, are associated with nonsyndromic deafness (DFNB48) and Usher syndrome type 1J (USH1J). One mutation in CIB2 is a prevalent cause of deafness DFNB48 in Pakistan; other CIB2 mutations contribute to deafness elsewhere in the world. In mice, CIB2 is localized to the mechanosensory stereocilia of inner ear hair cells and to retinal photoreceptor and pigmented epithelium cells. Consistent with molecular modeling predictions of calcium binding, CIB2 significantly decreased the ATP-induced calcium responses in heterologous cells, whereas mutations in deafness DFNB48 altered CIB2 effects on calcium responses. Furthermore, in zebrafish and Drosophila melanogaster, CIB2 is essential for the function and proper development of hair cells and retinal photoreceptor cells. We also show that CIB2 is a new member of the vertebrate Usher interactome.

Screening of 38 genes identifies mutations in 62% of families with nonsyndromic deafness in Turkey.

More than 60% of prelingual deafness is genetic in origin, and of these up to 95% are monogenic autosomal recessive traits. Causal mutations have been identified in 1 of 38 different genes in a subset of patients with nonsyndromic autosomal recessive deafness. In this study, we screened 49 unrelated Turkish families with at least three affected children born to consanguineous parents. Probands from all families were negative for mutations in the GJB2 gene, two large deletions in the GJB6 gene, and the 1555A>G substitution in the mitochondrial DNA MTRNR1 gene. Each family was subsequently screened via autozygosity mapping with genomewide single-nucleotide polymorphism arrays. If the phenotype cosegregated with a haplotype flanking one of the 38 genes, mutation analysis of the gene was performed. We identified 22 different autozygous mutations in 11 genes, other than GJB2, in 26 of 49 families, which overall explains deafness in 62% of families. Relative frequencies of genes following GJB2 were MYO15A (9.9%), TMIE (6.6%), TMC1 (6.6%), OTOF (5.0%), CDH23 (3.3%), MYO7A (3.3%), SLC26A4 (1.7%), PCDH15 (1.7%), LRTOMT (1.7%), SERPINB6 (1.7%), and TMPRSS3 (1.7%). Nineteen of 22 mutations are reported for the first time in this study. Unknown rare genes for deafness appear to be present in the remaining 23 families.

Recurrent and private MYO15A mutations are associated with deafness in the Turkish population.

The identities and frequencies of MYO15A mutations associated with hearing loss in different populations remained largely unknown. We screened the MYO15A gene for mutations in 104 unrelated multiplex and consanguineous Turkish families with autosomal recessive nonsyndromic sensorineural hearing loss using autozygosity mapping. The screening of MYO15A in 10 families mapped to the DFNB3 locus revealed five previously unreported mutations: p.Y289X (1 family), p.V1400M (1 family), p.S1481P (1 family), p.R1937TfsX10 (3 families), and p.S3335AfsX121 (2 families). Recurrent mutations were associated with conserved haplotypes suggesting the presence of founder effects. Severe to profound sensorineural hearing loss was observed in all subjects with homozygous mutations except for two members of a family who were homozygous for the p.Y289X mutation in the N-terminal extension domain and had considerable residual hearing. We estimate the prevalence of homozygous MYO15A mutations in autosomal recessive nonsyndromic deafness in Turkey as 0.062 (95% confidence interval is 0.020-0.105).

Mutations in TMC1 contribute significantly to nonsyndromic autosomal recessive sensorineural hearing loss: a report of five novel mutations.

Genome wide homozygosity mapping using Affymetrix 10K arrays revealed the DFNB7/11 locus including the TMC1 gene in 5 of 35 Turkish families with autosomal recessive nonsyndromic severe to profound congenital or prelingual-onset sensorineural hearing loss (SNHL). Additional 51 families were later screened for co-segregation of the locus with the phenotype using microsatellite markers. GJB2 and mtDNA A1555G mutations were negative in probands from each family. Mutation analysis was performed in families showing co-segregation of autosomal recessive SNHL with haplotypes at the DFNB7/11 locus. A total of six different mutations in seven families were identified, including novel missense alterations, p.G444R (c.1330G>A), p.R445C (c.1333C>T), and p.I677T (c.2030T>C), one novel splice site mutation IVS6+2 T>A (c.64+2T>A), and a novel large deletion of approximately 31kb at the 3' region of the gene including exons 19-24, as well as a previously reported nonsense mutation, p.R34X (c.100C>T). All identified mutations co-segregated with autosomal recessive SNHL in all families and were not found in Turkish hearing controls. These results expand the mutation spectrum of TMC1 with five novel mutations and provide data for the significant contribution of TMC1 mutations in hearing loss.

Homozygous mutations in fibroblast growth factor 3 are associated with a new form of syndromic deafness characterized by inner ear agenesis, microtia, and microdontia.

We identified nine individuals from three unrelated Turkish families with a unique autosomal recessive syndrome characterized by type I microtia, microdontia, and profound congenital deafness associated with a complete absence of inner ear structures (Michel aplasia). We later demonstrated three different homozygous mutations (p.S156P, p.R104X, and p.V206SfsX117) in the fibroblast growth factor 3 (FGF3) gene in affected members of these families, cosegregating with the autosomal recessive transmission as a completely penetrant phenotype. These findings demonstrate the involvement of FGF3 mutations in a human malformation syndrome for the first time and contribute to our understanding of the role this gene plays in embryonic development. Of particular interest is that the development of the inner ear is completely disturbed at a very early stage--or the otic vesicle is not induced at all--in all of the affected individuals who carried two mutant FGF3 alleles.