Dysfunction of GRAP, encoding the GRB2-related adaptor protein, is linked to sensorineural hearing loss.

We have identified a GRAP variant (c.311A>T; p.Gln104Leu) cosegregating with autosomal recessive nonsyndromic deafness in two unrelated families. GRAP encodes a member of the highly conserved growth factor receptor-bound protein 2 (GRB2)/Sem-5/drk family of proteins, which are involved in Ras signaling; however, the function of the growth factor receptor-bound protein 2 (GRB2)-related adaptor protein (GRAP) in the auditory system is not known. Here, we show that, in mouse, Grap is expressed in the inner ear and the protein localizes to the neuronal fibers innervating cochlear and utricular auditory hair cells. Downstream of receptor kinase (drk), the Drosophila homolog of human GRAP, is expressed in Johnston's organ (JO), the fly hearing organ, and the loss of drk in JO causes scolopidium abnormalities. drk mutant flies present deficits in negative geotaxis behavior, which can be suppressed by human wild-type but not mutant GRAP. Furthermore, drk specifically colocalizes with synapsin at synapses, suggesting a potential role of such adaptor proteins in regulating actin cytoskeleton dynamics in the nervous system. Our findings establish a causative link between GRAP mutation and nonsyndromic deafness and suggest a function of GRAP/drk in hearing.

GJB2 mutations in Mongolia: complex alleles, low frequency, and reduced fitness of the deaf.

We screened the GJB2 gene for mutations in 534 (108 multiplex and 426 simplex) probands with non-syndromic sensorineural deafness, who were ascertained through the only residential school for the deaf in Mongolia, and in 217 hearing controls. Twenty different alleles, including four novel changes, were identified. Biallelic GJB2 mutations were found in 4.5% of the deaf probands (8.3% in multiplex, 3.5% in simplex). The most common mutations were c.IVS1 + 1G > A (c.-3201G > A) and c.235delC with allele frequencies of 3.5% and 1.5%, respectively. The c.IVS1 + 1G > A mutation appears to have diverse origins based on associated multiple haplotypes. The p.V27I and p.E114G variants were frequently detected in both deaf probands and hearing controls. The p.E114G variant was always in cis with the p.V27I variant. Although in vitro experiments using Xenopus oocytes have suggested that p.[V27I;E114G] disturbs the gap junction function of Cx26, the equal distribution of this complex allele in both deaf probands and hearing controls makes it a less likely cause of profound congenital deafness. We found a lower frequency of assortative mating (37.5%) and decreased genetic fitness (62%) of the deaf in Mongolia as compared to the western populations, which provides an explanation for lower frequency of GJB2 deafness in Mongolia.

Ripor2 is involved in auditory hair cell stereociliary bundle structure and orientation.

RIPOR2 (previously known as FAM65B) localizes to stereocilia of auditory hair cells and causes deafness when its function is disturbed by mutations. Here, we demonstrate that during the morphogenesis of the hair cell bundle, absence of Ripor2 affects the orientation of this key subcellular structure. We show that Ripor2 interacts with Myh9, a protein encoded by a known deafness gene. Absence of Ripor2 is associated with low Myh9 abundance in the mouse cochlea despite increased amount of Myh9 transcripts. While Myh9 is mainly expressed in stereocilia, a phosphorylated form of Myh9 is particularly enriched in the kinocilium. In Ripor2-deficient mice, kinocilium shows an aberrant localization which associates with a reduced content of phosphorylated Myh9. Acetylated alpha tubulin, another specific kinociliary protein which contributes to microtubule stabilization, is reduced in the absence of Ripor2 as well. We propose that Ripor2 deficiency influences abundance and/or post-translational modifications of proteins expressed in both stereocilia and kinocilia. This effect may have a negative impact on the structure and function of the auditory hair cell bundle.

Monosomy chromosome 21 compensated by 21q22.11q22.3 duplication in a case with small size and minor anomalies.

BACKGROUND: Partial monosomy 21 is a rare finding with variable sizes and deletion breakpoints, presenting with a broad spectrum of phenotypes. CASE PRESENTATION: We report a 10-month-old boy with short stature, minor anomalies and mild motor delay. The patient had a monosomy 21 and duplication of the 21q22.11q22.3 region on the remaining derivative chromosome 21 which represents a partial 21q uniparental disomy of paternal origin, upd(21q22.11q22.3)pat. The abnormalities were characterized by karyotyping, FISH, chromosomal microarray, and genotyping. CONCLUSIONS: This is the first case showing a monosomy 21 compensated by upd(21q22.11q22.3) as a mechanism of genomic rescue. Because there is no strong evidence showing imprinting on chromosome 21, the uniparental disomy itself is not associated with abnormal phenotype but has reduced phenotype severity of monosomy 21. We reviewed the previously published cases with isolated 21q deletions and identified a common deletion of 5.7 Mb associated with low birth weight, length and head circumference in the 21q21.2 region.

Identification of candidate gene FAM183A and novel pathogenic variants in known genes: High genetic heterogeneity for autosomal recessive intellectual disability.

The etiology of intellectual disability (ID) is heterogeneous including a variety of genetic and environmental causes. Historically, most research has not focused on autosomal recessive ID (ARID), which is a significant cause of ID, particularly in areas where parental consanguinity is common. Identification of genetic causes allows for precision diagnosis and improved genetic counseling. We performed whole exome sequencing to 21 Turkish families, seven multiplex and 14 simplex, with nonsyndromic ID. Based on the presence of multiple affected siblings born to unaffected parents and/or shared ancestry, we consider all families as ARID. We revealed the underlying causative variants in seven families in MCPH1 (c.427dupA, p.T143Nfs*5), WDR62 (c.3406C>T, p.R1136*), ASPM (c.5219_5225delGAGGATA, p.R1740Tfs*7), RARS (c.1588A>G, p.T530A), CC2D1A (c.811delG, p.A271Pfs*30), TUSC3 (c.793C>T, p.Q265*) and ZNF335 (c.808C>T, p.R270C and c.3715C>A, p.Q1239K) previously linked with ARID. Besides ARID genes, in one family, affected male siblings were hemizygous for PQBP1 (c.459_462delAGAG, p.R153Sfs*41) and in one family the proband was female and heterozygous for X-chromosomal SLC9A6 (c.1631+1G>A) variant. Each of these variants, except for those in MCPH1 and PQBP1, have not been previously published. Additionally in one family, two affected children were homozygous for the c.377G>A (p.W126*) variant in the FAM183A, a gene not previously associated with ARID. No causative variants were found in the remaining 11 families. A wide variety of variants explain half of families with ARID. FAM183A is a promising novel candidate gene for ARID.

SLC26A4 mutations are associated with a specific inner ear malformation.

BACKGROUND AND AIM: Inner ear anomalies have been reported in approximately 30% of children with early onset deafness. Identification of causative genetic factors in a large proportion of these patients was not successful. Mutations in the SLC26A4 gene have been detected in individuals with enlarged vestibular aqueduct (EVA) or Mondini dysplasia. We aimed to characterize the inner ear anomalies associated with SLC26A4 mutations. METHODS: The SLC26A4 gene has been screened for mutations in 16 subjects from 14 unrelated Turkish families with a variety of inner ear anomalies ranging from Michel aplasia to incomplete partition-II and EVA. None of the patients was diagnosed to have a recognizable genetic syndrome. Additional four patients with Pendred syndrome from three families were included. RESULTS: Only one patient with EVA was found to have a heterozygous mutation (c.1586delT) in SLC26A4. All patients with Pendred syndrome had homozygous mutations and were noted to have either EVA or EVA associated with incomplete partition-II on the computed tomography of the temporal bone. CONCLUSION: SLC26A4 mutations are not associated with a large spectrum of inner ear anomalies. They, instead, result in a specific morphological appearance consistent with EVA or incomplete partition-II.

Dominant deafness-onychodystrophy syndrome caused by an ATP6V1B2 mutation.

Our report clarifies the role of ATP6V1B2 in patients with deafness and onycho-osteodystrophy and confirms that a recurring ATP6V1B2 c.1516C>T [p.(Arg506*)], variant causes dominant deafness-onychodystrophy (DDOD) syndrome.

Novel EYA1 variants causing Branchio-oto-renal syndrome.

INTRODUCTION: Branchio-oto-renal (BOR) syndrome is an autosomal dominant genetic disorder characterized by second branchial arch anomalies, hearing impairment, and renal malformations. Pathogenic mutations have been discovered in several genes such as EYA1, SIX5, and SIX1. However, nearly half of those affected reveal no pathogenic variant by traditional genetic testing. METHODS AND MATERIALS: Whole Exome sequencing and/or Sanger sequencing performed in 10 unrelated families from Turkey, Iran, Ecuador, and USA with BOR syndrome in this study. RESULTS: We identified causative DNA variants in six families including novel c.525delT, c.979T > C, and c.1768delG and a previously reported c.1779A > T variants in EYA1. Two large heterozygous deletions involving EYA1 were detected in additional two families. Whole exome sequencing did not reveal a causative variant in the remaining four families. CONCLUSIONS: A variety of DNA changes including large deletions underlie BOR syndrome in different populations, which can be detected with comprehensive genetic testing.

Novel pathogenic variants underlie SLC26A4-related hearing loss in a multiethnic cohort.

OBJECTIVES: The genetics of sensorineural hearing loss is characterized by a high degree of heterogeneity. Despite this heterogeneity, DNA variants found within SLC26A4 have been reported to be the second most common contributor after those of GJB2 in many populations. METHODS: Whole exome sequencing and/or Sanger sequencing of SLC26A4 in 117 individuals with sensorineural hearing loss with or without inner ear anomalies but not with goiter from Turkey, Iran, and Mexico were performed. RESULTS: We identified 27 unique SLC26A4 variants in 31 probands. The variants c.1673A > G (p.N558S), c.1708-1G > A, c.1952C > T (p.P651L), and c.2090-1G > A have not been previously reported. The p.N558S variant was detected in two unrelated Mexican families. CONCLUSION: A range of SLC26A4 variants without a common recurrent mutation underlies SLC26A4-related hearing loss in Turkey, Iran, and Mexico.

Audiological findings in Noonan syndrome.

OBJECTIVES: The aim of this study was to evaluate audiologic properties of patients with Noonan syndrome and compare these findings with those of unaffected peers. METHODS: The study included 17 children with Noonan syndrome and 20 typically developing children without Noonan syndrome. Pure tone and speech audiometry, immitancemetric measurement, otoacoustic emissions measurement and auditory brainstem response tests were applied to all (n = 37) children. RESULTS: Hearing thresholds of children with Noonan syndrome were higher (poorer) than those observed unaffected peers, while the hearing sensitivity of the both groups were normal limits (p = 0.013 for right, p = 0.031 for left ear). Transient evoked otoacoustic emissions amplitudes of the children with Noonan syndrome were lower than the children without Noonan syndrome (p = 0.005 for right, p = 0.002 for left ear). Middle ear pressures and auditory brainstem response values were within normal limits and there was no difference between the two groups (p > 0.05). CONCLUSION: General benefit of the present study is to characterize the audiologic findings of children with Noonan syndrome, which is beneficial in clinics evaluating children with Noonan syndrome.

HPSE2 mutations in urofacial syndrome, non-neurogenic neurogenic bladder and lower urinary tract dysfunction.

BACKGROUND: Urofacial syndrome (UFS) is characterised by congenital bladder dysfunction accompanied by a characteristic abnormal grimace upon smiling and crying. In recent years, biallelic mutations of HPSE2 and LRIG2 have been reported in UFS patients. Non-neurogenic neurogenic bladder (NNNB) has a bladder identical to UFS without typical facial features. The aim of this study was to analyse HPSE2 mutations in patients with UFS and NNNB or severe lower urinary tract dysfunction (LUTD) without abnormal facial expression. METHODS: Patients with UFS, NNNB and severe LUTD were enrolled in the study. We examined a total of 35 patients from 33 families. There were seven UFS patients from five different families, 21 patients with NNNB and seven with LUTD. HPSE2 gene mutation analysis was performed using the polymerase chain reaction protocol followed by Sanger sequencing in these patients. RESULTS: A twin pair with UFS was found to be homozygous for c.457C>T (p.Arg153*) mutation. No other pathogenetic variant was detected. CONCLUSION: HPSE2 mutations were found in one UFS family but not detected in patients with NNNB and severe LUTD. Considering the increasingly recognised cases of NNNB that were diagnosed in early childhood period, genetic factors appear to be responsible. Thus, further genetic studies are needed to discover novel associated gene variants in these bladder anomalies.

Identification of copy number variants through whole-exome sequencing in autosomal recessive nonsyndromic hearing loss.

Genetic variants account for more than half of the cases with congenital or prelingual onset hearing loss. Autosomal recessive nonsyndromic hearing loss (ARNSHL) is the most common subgroup. Whole-exome sequencing (WES) has been shown to be effective detecting deafness-causing single-nucleotide variants (SNVs) and insertion/deletions (INDELs). After analyzing the WES data for causative SNVs or INDELs involving previously reported deafness genes in 78 families with ARNSHL, we searched for copy number variants (CNVs) through two different tools in 24 families that remained unresolved. We detected large homozygous deletions in STRC and OTOA in single families. Thus, causative CNVs in known deafness genes explain 2 out of 78 (2.6%) families in our sample set. We conclude that CNVs can be reliably detected through WES and should be the part of pipelines used to clarify genetic basis of hearing loss.

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.

A FGF3 mutation associated with differential inner ear malformation, microtia, and microdontia.

OBJECTIVES/HYPOTHESIS: Analysis of association between genotype and phenotype. STUDY DESIGN: Prospective genetic study in a family. METHODS: Auditory investigations, computer tomography, and genetic sequencing of the fibroblast growth factor 3 (FGF3) gene were performed on a Somali family presenting with autosomal recessive, hearing impairment, microdontia, and outer ear morphologies ranging from normal auricle development to microtia assessed as type 1 Weerda dysplasia in affected individuals. RESULTS: Computed tomography imaging identified differential inter- and intraindividual malformations of the inner ear including labyrinth aplasia, development of a common cavity to the presence of a cochlear with 1.5 windings (Mondini malformation) in affected individuals, symptoms similar to those described as labyrinth aplasia, microtia, and microdontia (LAMM) syndrome, caused by mutations in FGF3. Genetic sequencing revealed the presence of a novel p.R95W missense mutation in FGF3 segregating with pathology. The p.R95W mutation substitutes a positively charged arginine for a polar tryptophan in the highly conserved RYLAM consensus of the beta 6 sheet of FGF3 that interacts with FGFR2. CONCLUSIONS: These findings describe, for the first time, variable inner ear malformations and outer ear dysplasia in the presence of constant microdontia, associated with homozygous inheritance of the p.R95W mutation in FGF3, mirroring phenotypes observed in mouse models ablating FGF3/FGFR2 signaling.

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.

Familial neonatal Marfan syndrome due to parental mosaicism of a missense mutation in the FBN1 gene.

We present a family in which three siblings were born with neonatal Marfan syndrome (MFS) to unaffected parents. The clinical findings included joint contractures, large ears, loose skin, ectopia lentis, muscular hypoplasia, aortic root dilatation, mitral and tricuspid valve insufficiency, and pulmonary emphysema. All three siblings died due to cardiorespiratory insufficiency by 2-4 months of age. Screening of the FBN1 gene showed the heterozygous c.3257G > A (p.Cys1086Tyr) mutation in the proband. Mosaicism of the mutation was demonstrated in the somatic cells and in the germ line of the father. Although three examples of parental mosaicism for classical MFS were demonstrated previously, this is the first report of familial occurrence of neonatal MFS due to a heterozygous mutation in FBN1. In conclusion, the p.Cys1086Tyr mutation in FBN1 is consistently associated with neonatal MFS. Parental mosaicism should always be kept in mind when counseling families with MFS.

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.