Xiuhong Pang

A dominant mutation in the stereocilia-expressing gene TBC1D24 is a probable cause for nonsyndromic hearing impairment.

Mutations in TBC1D24 have been linked to a variety of epileptic syndromes and recently to syndromic hearing impairment DOORS syndrome and nonsyndromic hearing impairment DFNB86. All TBC1D24 mutations reported so far were inherited in the recessive mode. In a dominant family segregated with late‐onset, progressive, nonsyndromic hearing impairment, linkage analysis revealed a 2.07 Mb candidate region on chromosome 16p13.3 that contains TBC1D24. Whole‐exome sequencing identified a heterozygous p.Ser178Leu variant of TBC1D24 as the only candidate mutation segregating with the hearing loss within the family. In perinatal mouse cochlea, we detected a restricted expression of Tbc1d24 in the stereocilia of the hair cells as well as in the spiral ganglion neurons. Our study suggested that the p.Ser178Leu mutation of TBC1D24 is a probable cause for dominant, nonsyndromic hearing impairment. Identification of TBC1D24 as the stereocilia‐expressing gene may shed new light on its specific function in the inner ear.

The homozygous p.V37I variant of GJB2 is associated with diverse hearing phenotypes

The homozygous p.V37I variant of GJB2 is frequent in East Asians and has been reported to have a pathogenic role in mild‐to‐moderate hearing impairment (HI). In this study, we investigated the prevalence and phenotypic spectrum of homozygous p.V37I in three Chinese Han cohorts with severe‐to‐profound HI (n = 857, Cohort S), mild‐to‐moderate HI (n = 88, Cohort M) and normal hearing (n = 1550, Cohort N). Sequencing of GJB2 showed that homozygous p.V37I was detected in 1.63% (14/857), 12.5% (11/88) and 0.32% (5/1550) of subjects in Cohorts S, M and N, respectively. It was strongly associated with both mild‐to‐moderate (p = 2.0 × 10−11) and severe‐to‐profound (p = 0.001) HI, but was estimated to have a rather low penetrance (17%). Among the hearing impaired subjects with homozygous p.V37I, the onset of HI was congenital in 65% (11/17) and delayed in 35% (6/17). By targeted next‐generation sequencing of 79 known deafness genes, we identified an additional homozygous pathogenic mutation of CDH23 in 1 of 14 p.V37I homozygous subjects from Cohort S. Our study suggested that homozygous p.V37I is associated with a broader spectrum of hearing phenotypes than previously revealed. Data presented in this study can be effectively applied to clinical evaluation and genetic counseling of people carrying this variant.

Targeted next-generation sequencing in Uyghur families with non-syndromic sensorineural hearing loss.

The mutation spectrum of deafness genes may vary in different ethnical groups. In this study, we investigated the genetic etiology of nonsyndromic deafness in four consanguineous and two multiplex Uyghur families in which mutations in common deafness genes GJB2, SLC26A4 and MT-RNR1 were excluded. Targeted next-generation sequencing of 97 deafness genes was performed in the probands of each family. Novel pathogenic mutations were identified in four probands including the p.L416R/p.A438T compound heterozygous mutations in TMC1, the homozygous p.V1880E mutation in MYO7A, c.1238delT frameshifting deletion in PCDH15 and c.9690+1G>A splice site mutation in MYO15A. Co-segregation of the mutations and the deafness were confirmed within each family by Sanger sequencing. No pathogenic mutations were identified in one multiplex family and one consanguineous family. Our study provided a useful piece of information for the genetic etiology of deafness in Uyghurs.

Association of GRM7 variants with different phenotype patterns of age-related hearing impairment in an elderly male Han Chinese population.

Several single nucleotide polymorphisms (SNPs) of the Glutamate metabotrophic receptor 7 gene (GRM7) have recently been identified by the genome-wide association study (GWAS) as potentially playing a role in susceptibility to age-related hearing impairment (ARHI), however this has not been validated in the Han Chinese population. The aim of this study was to determine if these SNPs are also associated with ARHI in an elderly male Han Chinese population. In this case-control candidate genes association study, a total of 982 men with ARHI and 324 normal-hearing controls subjects were studied. Using K-means cluster analysis, four audiogram shape subtypes of ARHI were identified in the case group: ‘‘flat shape (FL)’’, ‘‘sloping shape (SL)’’, ‘‘2-4 kHz abrupt loss (AL) shape’’ and ‘‘8 kHz dip (8D) shape’’. Results suggested that the SNP rs11928865 (A>T) of GRM7 was significantly associated with ARHI after adjusting for non-genetic factors (p= 0.000472, OR= 1.599, 95%CI= 1.229~2.081). Furthermore, frequency of TT genotype (rs11928865) were significant higher in the SL subgroup and AL subgroup with compared to controls group (p= 9.41E-05, OR= 1.945, 95%CI= 1.393~2.715; p= 0.000109, OR= 1.915, 95%CI= 1.378~2.661 adjusted, respectively) after Bonferroni correction. However, there wasn’t significant difference in the frequency of the TT genotype between cases in the FL subgroup or the 8D subgroup with when compared with controls. Results of the current study suggest that, in an elderly male Han Chinese population, GRM7 SNP rs11928865 (TT) occurs more frequently in ARHI patients with SL and AL phenotype patterns.

Mono-allelic mutations of SLC26A4 is over-presented in deaf patients with non-syndromic enlarged vestibular aqueduct.

OBJECTIVES Recessive mutations of SLC26A4 are the major cause of hearing impairment associated with enlarged vestibular aqueduct (EVA). In a significant percentage of non-syndromic EVA patients, however, only mono-allelic mutations of SLC26A4 can be identified. In this study, we aimed to evaluate whether presence of mono-allelic mutations of SLC26A4 in those patients was coincidental or etiologically associated with the disorder. METHODS The exons and flanking splicing sites of SLC26A4 were sequenced in 150 Chinese Han deaf probands with non-syndromic EVA. c.919-2A >G and p.H723R, two frequent mutations of SLC26A4 in Chinese Hans, were screened by an allele-specific PCR-based array in 3056 ethnically-matched normal hearing controls. The frequency of mono-allelic c.919-2A >G and p.H723R mutations was determined in each group. The statistical significance of the difference was analyzed by Fishers exact test. RESULTS Bi-allelic, mono-allelic and no mutation of SLC26A4 were detected in 98 (65.3%), 18 (12%) and 34 (22.67%) deaf probands with non-syndromic EVA, respectively. The frequency of mono-allelic c.919-2A >G and p.H723R mutations were significantly higher in the 150 deaf probands with non-syndromic EVA (8.67%) than in the 3056 normal hearing controls (1.4%, P=1.8×10(-6)). CONCLUSION Presence of mono-allelic mutations of SLC26A4 in non-syndromic EVA patients is etiologically associated with this disorder. Additional genetic or environmental causes may be present in those patients and demand further investigation and consideration during the genetic diagnosis and counseling.

Characterization of Spectrum, de novo Rate and Genotype-Phenotype Correlation of Dominant GJB2 Mutations in Chinese Hans

Dominant mutations in GJB2 may lead to various degrees of sensorineural hearing impairment and/or hyperproliferative epidermal disorders. So far studies of dominant GJB2 mutations were mostly limited to case reports of individual patients and families. In this study, we identified 7 families, 11 subjects with dominant GJB2 mutations by sequencing of GJB2 in 2168 Chinese Han probands with sensorineural hearing impairment and characterized the associated spectrum, de novo rate and genotype-phenotype correlation. We identified p.R75Q, p.R75W and p.R184Q as the most frequent dominant GJB2 mutations among Chinese Hans, which had a very high de novo rate (71% of probands). A majority (10/11) of subjects carrying dominant GJB2 mutations exhibited palmoplantar keratoderma in addition to hearing impairment. In two families segregated with additional c.235delC or p.V37I mutations of GJB2, family members with the compound heterozygous mutations exhibited more severe phenotype than those with single dominant GJB2 mutation. Our study suggested that the high de novo mutation rate gives rise to a significant portion of dominant GJB2 mutations. The severity of the hearing and epidermal phenotypes associated with dominant GJB2 mutations may be modified by additional recessive mutations of GJB2.

Mutation in the Hair Cell Specific Gene POU4F3 Is a Common Cause for Autosomal Dominant Nonsyndromic Hearing Loss in Chinese Hans

Autosomal dominant nonsyndromic hearing loss (ADNSHL) is extremely heterogeneous. So far the genetic etiological contribution of the gene POU4F3 associated with ADNSHL has been rarely reported. In our previous study, a c.603_604delGG mutation in the hair cell specific gene POU4F3 has been identified as the pathogenic cause in one of the seven Chinese Han ADNSHL families. In the present study, we performed targeted next-generation sequencing of 144 known deafness genes in another nine Chinese Han ADNSHL families and identified two more novel mutations in POU4F3, p.Leu311Pro and c.120+1G>C, as the pathogenic cause. Clinical characterization of the affected individuals in these three families showed that the three POU4F3 mutations may lead to progressive hearing loss with variable ages of onset and degrees of severity. Our results suggested that mutations in POU4F3 are a relatively common cause (3/16) for ADNSHL in Chinese Hans, which should be routinely screened in such cases during genetic testing.

Molecular etiology of non-dominant, non-syndromic, mild-to-moderate childhood hearing impairment in Chinese Hans

Childhood hearing impairment (HI) is genetically heterogeneous. Compared with the severe‐to‐profound HI, the molecular etiology of mild‐to‐moderate HI in children has been less well characterized, especially for those not inherited in the dominant mode. In this study, we recruited 114 probands with non‐dominant, non‐syndromic, mild‐to‐moderate childhood HI. Sequencing of GJB2, SLC26A4, and MTRNR1 identified causative mutations in 30.7% (35/114), 4.4% (5/114), and 4.4% (5/114) of subjects, respectively. A majority (62.9%) of bi‐allelic GJB2 mutations have non‐truncating mutations in at least one allele. In 10 multiplex probands with no GJB2, SLC26A4, and MTRNR1 mutations identified, targeted next‐generation sequencing (NGS) of 79 known deafness genes did not identify any additional causes. Our data showed that the molecular etiology of mild‐to‐moderate childhood HI is considerably different from what reported for severe‐to‐profound HI and far from complete for those inherited in non‐dominant modes.

Molecular etiology and genotype-phenotype correlation of Chinese Han deaf patients with type I and type II Waardenburg Syndrome.

Waardenburg syndrome (WS) characterized by sensorineural hearing loss and pigmentary abnormalities is genetically heterogeneous and phenotypically variable. This study investigated the molecular etiology and genotype-phenotype correlation of WS in 36 Chinese Han deaf probands and 16 additional family members that were clinically diagnosed with WS type I (WS1, n = 8) and type II (WS2, n = 42). Mutation screening of six WS-associated genes detected PAX3 mutations in 6 (86%) of the 7 WS1 probands. Among the 29 WS2 probands, 13 (45%) and 10 (34%) were identified with SOX10 and MITF mutations, respectively. Nineteen of the 26 detected mutations were novel. In WS2 probands whose parental DNA samples were available, de novo mutations were frequently seen for SOX10 mutations (7/8) but not for MITF mutations (0/5, P = 0.005). Excessive freckle, a common feature of WS2 in Chinese Hans, was frequent in WS2 probands with MITF mutations (7/10) but not in those with SOX10 mutations (0/13, P = 4.9 × 10−4). Our results showed that mutations in SOX10 and MITF are two major causes for deafness associated with WS2. These two subtypes of WS2 can be distinguished by the high de novo rate of the SOX10 mutations and the excessive freckle phenotype exclusively associated with the MITF mutations.

A Novel Missense Mutation of NOG Interferes With the Dimerization of NOG and Causes Proximal Symphalangism Syndrome in a Chinese Family

Objectives: NOG is an antagonist to bone morphogenetic proteins and plays an important role in proper bone and joint development. Dominant mutations in NOG may lead to a series of symphalangism spectrum disorders. In this study, we aimed to identify the genetic cause and the pathogenic mechanism of an autosomal dominant disorder with cosegregating proximal symphalangism and conductive hearing impairment in a Chinese family. Methods: Mutation screening of NOG was performed in the affected family members by polymerase chain reaction (PCR) amplification and direct sequencing. Western blotting analysis of NOG was performed in the leukocyte samples of the family members. Results: A novel p.W150C heterozygous mutation in NOG was identified cosegregating with the proximal symphalangism disorder in the family. Western blotting analysis showed that the p.W150C mutation interferes with the dimerization of the mutant NOG. Conclusions: Our results agreed with previously published results of in vitro studies and suggested that impaired dimerization of mutant NOG is an important pathogenic mechanism for the NOG-related symphalangism spectrum disorder.