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Hypo-functional SLC26A4 variants associated with nonsyndromic hearing loss and enlargement of the vestibular aqueduct: genotype-phenotype correlation or coincidental polymorphisms?

ABSTRACT: Hearing loss with enlargement of the vestibular aqueduct (EVA) can be associated with mutations of the SLC26A4 gene encoding pendrin, a transmembrane Cl(-)/I(-)/HCO(3)(-) exchanger. Pendrin's critical transport substrates are thought to be I(-) in the thyroid gland and HCO(3)(-) in the inner ear. We previously reported that bi-allelic SLC26A4 mutations are associated with Pendred syndromic EVA whereas one or zero mutant alleles are associated with nonsyndromic EVA. One study proposed a correlation of nonsyndromic EVA with SLC26A4 alleles encoding pendrin with residual transport activity. Here we describe the phenotypes and SLC26A4 genotypes of 47 EVA patients ascertained since our first report of 39 patients. We sought to determine the pathogenic potential of each variant in our full cohort of 86 patients. We evaluated the trafficking of 11 missense pendrin products expressed in COS-7 cells. Products that targeted to the plasma membrane were expressed in Xenopus oocytes for measurement of anion exchange activity. p.F335L, p.C565Y, p.L597S, p.M775T, and p.R776C had Cl(-)/I(-) and Cl(-)/HCO(3)(-) exchange rate constants that ranged from 13 to 93% of wild type values. p.F335L, p.L597S, p.M775T and p.R776C are typically found as mono-allelic variants in nonsyndromic EVA. The high normal control carrier rate for p.L597S indicates it is a coincidentally detected nonpathogenic variant in this context. We observed moderate differential effects of hypo-functional variants upon exchange of HCO(3)(-) versus I(-) but their magnitude does not support a causal association with nonsyndromic EVA. However, these alleles could be pathogenic in trans configuration with a mutant allele in Pendred syndrome.

SUBMITTER: Choi BY

PROVIDER: S-EPMC2663020 | biostudies-literature | 2009 Apr

REPOSITORIES: biostudies-literature

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Hypo-functional SLC26A4 variants associated with nonsyndromic hearing loss and enlargement of the vestibular aqueduct: genotype-phenotype correlation or coincidental polymorphisms?

Choi Byung Yoon BY Stewart Andrew K AK Madeo Anne C AC Pryor Shannon P SP Lenhard Suzanne S Kittles Rick R Eisenman David D Kim H Jeffrey HJ Niparko John J Thomsen James J Arnos Kathleen S KS Nance Walter E WE King Kelly A KA Zalewski Christopher K CK Brewer Carmen C CC Shawker Thomas T Reynolds James C JC Butman John A JA Karniski Lawrence P LP Alper Seth L SL Griffith Andrew J AJ

Human mutation 20090401 4

Hearing loss with enlargement of the vestibular aqueduct (EVA) can be associated with mutations of the SLC26A4 gene encoding pendrin, a transmembrane Cl(-)/I(-)/HCO(3)(-) exchanger. Pendrin's critical transport substrates are thought to be I(-) in the thyroid gland and HCO(3)(-) in the inner ear. We previously reported that bi-allelic SLC26A4 mutations are associated with Pendred syndromic EVA whereas one or zero mutant alleles are associated with nonsyndromic EVA. One study proposed a correlati ...[more]

PMID: 19204907

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Project description:BACKGROUND:Recessive mutations of coding regions and splice sites of the SLC26A4 gene cause hearing loss with enlargement of the vestibular aqueduct (EVA). Some patients also have a thyroid iodination defect that can lead to multinodular goiter as part of Pendred syndrome. A haplotype of variants upstream of SLC26A4, called CEVA, acts as a pathogenic recessive allele in trans to mutations affecting the coding regions or splice sites of SLC26A4. Our first hypothesis is that CEVA, acting as a pathogenic recessive allele, is correlated with a less severe phenotype than mutations affecting the coding regions and splice sites of SLC26A4. Our second hypothesis is that CEVA acts as a modifier of the phenotype in patients with EVA caused by mutations affecting the coding regions or splice sites of both alleles of SLC26A4 or EVA caused by other factors. METHODS:This was a prospective cohort study of 114 individuals and 202 ears with EVA. To test our first hypothesis, we compared the thyroid and auditory phenotypes of subjects with mutations affecting coding regions of both alleles of SLC26A4 with those of subjects carrying CEVA in trans to mutations affecting the coding regions. To test our second hypothesis, we compared the phenotypes associated with the presence versus absence of CEVA among subjects with no coding region mutations, as well as among subjects with mutations affecting coding regions of both alleles. RESULTS:Subjects carrying CEVA in trans to a mutation of SLC26A4 have a normal thyroid phenotype and less severe hearing loss in comparison to individuals with mutations affecting coding regions of both alleles of SLC26A4. In subjects with no mutant alleles of SLC26A4, hearing loss was more severe in subjects who carry the CEVA haplotype in comparison to non-carriers. There was no correlation of CEVA with the phenotype of subjects with mutations affecting coding regions of both alleles. CONCLUSIONS:CEVA, acting as a likely pathogenic recessive allele, is associated with a less severe phenotype than alleles with a mutation affecting the coding regions or splice sites of SLC26A4. CEVA may act as a genetic modifier in patients with EVA caused by other factors.

Project description:BackgroundNonsyndromic enlargement of vestibular aqueduct (NSEVA) is an autosomal recessive hearing loss disorder that is associated with mutations in SLC26A4. However, not all patients with NSEVA carry biallelic mutations in SLC26A4. A recent study proposed that single mutations in both SLC26A4 and KCNJ10 lead to digenic NSEVA. We examined whether KCNJ10 excert a role in the pathogenesis of NSEVA in Chinese patients.MethodsSLC26A4 was sequenced in 1056 Chinese patients with NSEVA. KCNJ10 was screened in 131 patients who lacked mutations in either one or both alleles of SLC26A4. Additionally, KCNJ10 was screened in 840 controls, including 563 patients diagnosed with NSEVA who carried biallelic SLC26A4 mutations, 48 patients with nonsyndromic hearing loss due to inner ear malformations that did not involve enlargement of the vestibular aqueduct (EVA), 96 patients with conductive hearing loss due to various causes, and 133 normal-hearing individuals with no family history of hereditary hearing loss.Results925 NSEVA patients were found carrying two-allele pathogenic SLC26A4 mutations. The most frequently detected KCNJ10 mutation was c.812G>A (p.R271H). Compared with the normal-hearing control subjects, the occurrence rate of c.812G>A in NSEVA patients with lacking mutations in one or both alleles of SLC26A4 had no significant difference(1.53% vs. 5.30%, χ(2) = 2.798, p = 0.172), which suggested that it is probably a nonpathogenic benign variant. KCNJ10 c.1042C>T (p.R348C), the reported EVA-related mutation, was not found in patients with NSEVA who lacked mutations in either one or both alleles of SLC26A4. Furthermore, the normal-hearing parents of patients with NSEVA having two SLC26A4 mutations carried the KCNJ10 c.1042C>T or c.812G>A mutation and a SLC26A4 pathogenic mutation.ConclusionSLC26A4 is the major genetic cause in Chinese NSEVA patients, accounting for 87.59%. KCNJ10 may not be a contributor to NSEVA in Chinese population. Other genetic or environmental factors are possibly play a role in the etiology of Chinese EVA patients with zero or monoallelic SLC26A4 mutation.

Dataset Information

Hypo-functional SLC26A4 variants associated with nonsyndromic hearing loss and enlargement of the vestibular aqueduct: genotype-phenotype correlation or coincidental polymorphisms?

Publications

Hypo-functional SLC26A4 variants associated with nonsyndromic hearing loss and enlargement of the vestibular aqueduct: genotype-phenotype correlation or coincidental polymorphisms?

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