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.

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.

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.

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.

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.

Branchio-oculo-facial syndrome in a newborn caused by a novel TFAP2A mutation

We present an 18-day old boy with bilateral cervical cutaneous defect in the retroauricular region, low-set and posteriorly rotated ears, bilateral microphtalmia and bilateral pseudocleft of the upper lip. Histopathological evaluation of cervical cutaneous defect showed ulceration on the surface and ectopic thymus tissue in the deep dermis with cortex, medulla and Hassal's corpuscles. Clinical findings led to the diagnosis of Branchio-oculo-facial syndrome, characterized by branchial defects (erythematous cutaneous defects in cervical region), ocular anomalies (microphthalmia, anophthalmia, lacrimal duct obstruction, coloboma, cataract, ptosis) and facial defects (cleft lip and/or palate, pseudocleft or abnormal philtrum). DNA sequencing showed a novel heterozygous mutation, c.731T>C (p.L244P), in TFAP2A gene confirming the diagnosis of this rare autosomal dominant developmental disorder with variable clinical findings.

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.

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.

Homozygous FGF3 mutations result in congenital deafness with inner ear agenesis, microtia, and microdontia

Homozygous mutations in the fibroblast growth factor 3 (FGF3) gene have recently been discovered in an autosomal recessive form of syndromic deafness characterized by complete labyrinthine aplasia (Michel aplasia), microtia, and microdontia (OMIM 610706 - LAMM). In order to better characterize the phenotypic spectrum associated with FGF3 mutations, we sequenced the FGF3 gene in 10 unrelated families in which probands had congenital deafness associated with various inner ear anomalies, including Michel aplasia, with or without tooth or external ear anomalies. FGF3 sequence changes were not found in eight unrelated probands with isolated inner ear anomalies or with a cochlear malformation along with auricle and tooth anomalies. We identified two new homozygous FGF3 mutations, p.Leu6Pro (c.17T>C) and p. Ile85MetfsX15 (c.254delT), in four subjects from two unrelated families with LAMM. The p.Leu6Pro mutation occurred within the signal site of FGF3 and is predicted to impair its secretion. The c.254delT mutation results in truncation of FGF3. Both mutations completely co-segregated with the phenotype, and heterozygotes did not have any of the phenotypic findings of LAMM. Some affected children had large skin tags on the upper side of the auricles, which is a distinctive clinical component of the syndrome. Enlarged collateral emissary veins associated with stenosis of the jugular foramen were noted on computerized tomographies of most affected subjects with FGF3 mutations. However, similar venous anomalies were also detected in persons with non-syndromic Michel aplasia, suggesting that a direct causative role of impaired FGF3 signaling is unlikely.

The effect of p.Arg25Cys alteration in NKX2-5 on conotruncal heart anomalies: mutation or polymorphism?

Heterozygous mutations in the NKX2-5 gene of patients with various congenital heart defects have been reported. Most of the congenital heart defects associated with the mutations in the NKX2-5 gene are conotruncal heart anomalies, primarily the tetralogy of Fallot. In this study, the authors screened 72 Turkish children with conotruncal heart anomalies and 185 healthy control subjects to find the NKX2-5 alterations. They found one previously documented NKX2-5 missense alteration, heterozygous c.73C>T (p.Arg25Cys), in a 10-year-old boy with tetralogy of Fallot. The same heterozygous alteration was found also in the patient's healthy father and in two unrelated persons in the healthy control group. The current study shows for the first time the presence of p.Arg25Cys in healthy control subjects other than African Americans. These results show that no genetic support exists for the pathogenecity of this alteration, although a previous in vitro study and theoretical predictions suggest a structural/functional difference in the altered protein region.