Search

Background Enlargement of the vestibular aqueduct (EVA) is the most common radiological abnormality in children with sensorineural hearing loss. Mutations in coding regions and splice sites of the SLC26A4 gene are often detected in Caucasians with EVA. Approximately one-fourth of patients with EVA have two mutant alleles (M2), one-fourth have one mutant allele (M1) and one-half have no mutant alleles (M0). The M2 genotype is correlated with a more severe phenotype. Methods We performed genotype–haplotype analysis and massively parallel sequencing of the SLC26A4 region in patients with M1 EVA and their families. Results We identified a shared novel haplotype, termed CEVA (Caucasian EVA), composed of 12 uncommon variants upstream of SLC26A4 . The presence of the CEVA haplotype on seven of ten ‘mutation-negative’ chromosomes in a National Institutes of Health M1 EVA discovery cohort and six of six mutation-negative chromosomes in a Danish M1 EVA replication cohort is higher than the observed prevalence of 28 of 1006 Caucasian control chromosomes (p Conclusions The CEVA haplotype causally contributes to most cases of Caucasian M1 EVA and, possibly, some cases of M0 EVA. The CEVA haplotype of SLC26A4 defines the most common allele associated with hereditary hearing loss in Caucasians. The diagnostic yield and prognostic utility of sequence analysis of SLC26A4 exons and splice sites will be markedly increased by addition of testing for the CEVA haplotype.

Enlargement of the vestibular aqueduct (EVA) is the most common radiological abnormality in children with sensorineural hearing loss. Mutations in coding regions and splice sites of theWe performed genotype-haplotype analysis and massively parallel sequencing of theWe identified a shared novel haplotype, termed CEVA (Caucasian EVA), composed of 12 uncommon variants upstream ofThe CEVA haplotype causally contributes to most cases of Caucasian M1 EVA and, possibly, some cases of M0 EVA. The CEVA haplotype of

Background Recessive mutant alleles of MYO7A , USH1C , CDH23 , and PCDH15 cause non-syndromic deafness or type 1 Usher syndrome (USH1) characterised by deafness, vestibular areflexia, and vision loss due to retinitis pigmentosa. For CDH23 , encoding cadherin 23, non-syndromic DFNB12 deafness is associated primarily with missense mutations hypothesised to have residual function. In contrast, homozygous nonsense, frame shift, splice site, and some missense mutations of CDH23 , all of which are presumably functional null alleles, cause USH1D. The phenotype of a CDH23 compound heterozygote for a DFNB12 allele in trans configuration to an USH1D allele is not known and cannot be predicted from current understanding of cadherin 23 function in the retina and vestibular labyrinth. Methods and results To address this issue, this study sought CDH23 compound heterozygotes by sequencing this gene in USH1 probands, and families segregating USH1D or DFNB12. Five non-syndromic deaf individuals were identified with normal retinal and vestibular phenotypes that segregate compound heterozygous mutations of CDH23 , where one mutation is a known or predicted USH1 allele. Conclusions One DFNB12 allele in trans configuration to an USH1D allele of CDH23 preserves vision and balance in deaf individuals, indicating that the DFNB12 allele is phenotypically dominant to an USH1D allele. This finding has implications for genetic counselling and the development of therapies for retinitis pigmentosa in Usher syndrome. Accession numbers The cDNA and protein Genbank accession numbers for CDH23 and cadherin 23 used in this paper are AY010111.2 and AAG27034.2, respectively.

Background: Hearing loss with enlarged vestibular aqueduct (EVA) can be inherited as an autosomal recessive trait caused by bi-allelic mutations of SLC26A4. However, many EVA patients have non-diagnostic SLC26A4 genotypes with only one or no detectable mutant alleles. Methods and results: In this study, the authors were unable to detect occult SLC26A4 mutations in EVA patients with non-diagnostic genotypes by custom comparative genomic hybridisation (CGH) microarray analysis or by sequence analysis of conserved non-coding regions. The authors sought to compare the segregation of EVA among 71 families with two (M2), one (M1) or no (M0) detectable mutant alleles of SLC26A4. The segregation ratios of EVA in the M1 and M2 groups were similar, but the segregation ratio for M1 was significantly higher than in the M0 group. Haplotype analyses of SLC26A4-linked STR markers in M0 and M1 families revealed discordant segregation of EVA with these markers in eight of 24 M0 families. Conclusion: The results support the hypothesis of a second, undetected SLC26A4 mutation that accounts for EVA in the M1 patients, in contrast to non-genetic factors, complex inheritance, or aetiologic heterogeneity in the M0 group of patients. These results will be helpful for counselling EVA families with non-diagnostic SLC26A4 genotypes.

Enlargement of the vestibular aqueduct (EVA) and its contents, the endolymphatic sac and duct, is the most common radiologic malformation of the inner ear associated with sensorineural hearing loss.1 It may occur alone or in combination with an incomplete partition of the apical turn of the cochlea as part of a complex of malformations known as a Mondini deformity.2 Hearing loss in ears with EVA is typically pre- or perilingual in onset, sensorineural or mixed, and fluctuating or progressive. EVA may be unilateral or bilateral; asymmetry of the hearing loss and the anatomic defect is common in bilateral cases.3–5 EVA has been observed in Pendred syndrome (PS; MIM 274600),6 branchio-oto-renal syndrome (MIM 113650),7 CHARGE (MIM 214800),8 Waardenburg syndrome (MIM 193500, 193510, 600193, 606662),9 and distal renal tubular acidosis with deafness (MIM 267300).10 Familial non-syndromic hearing loss with EVA was described in 199611 and numerous subsequent reports (DFNB4 (MIM 600791), enlarged vestibular aqueduct syndrome (MIM 603545)). EVA is always detected when the ears of individuals with PS are evaluated by both computed tomography (CT) and magnetic resonance imaging (MRI),6 and it has been estimated that PS may comprise up to 10% of prelingual deafness worldwide.3,12,13 PS is inherited in an autosomal recessive manner and is comprised of bilateral hearing loss, EVA, and an iodine organification defect in the thyroid gland, which may lead to goitre. PS is clinically differentiated from non-syndromic EVA by the presence of the thyroid iodine organification defect because goitre is an incompletely penetrant feature of PS.3 When goitre does occur in PS, it is most often euthyroidal and not evident until the second decade of life.3,12,14,15 There can be intrafamilial variability of the goitre, and PS phenocopies with …

Familial hypertrophic cardiomyopathy (FHC) is typically characterised by left ventricular hypertrophy, diastolic dysfunction, and hypercontractility, and is often associated with disabling symptoms, arrhythmias, and sudden death.1 FHC shows both non-allelic and allelic genetic heterogeneity, and results from any one of more than 100 mutations in genes encoding sarcomeric proteins.2 Identified genes include those encoding β myosin heavy chain, the myosin regulatory and essential light chains, myosin binding protein C, troponin I, troponin C, α cardiac actin, and titin.2,3 The FHC phenotype is characterised by hypertrophy, myocyte disarray and fibrosis, and results from the dominant negative expression of one of these (mainly missense) mutations. The resulting sarcomeric dysfunction leads ultimately, through mechanisms that remain obscure, to pathological left ventricular remodelling. However, as molecular defects are identified in only half the cases, it is likely that non-sarcomeric genes may also be responsible. Non-sarcomeric causes of FHC are largely uncharacterised, and may be associated with distinct or compound phenotypes. Similarly, hereditary sensorineural hearing loss shows a great degree of non-allelic and allelic genetic heterogeneity, and can be dominant, recessive, X linked, or mitochondrial.4–6 Hereditary sensorineural hearing loss is classified according to mode of inheritance and the presence of clinically detectable extra-auditory manifestations (syndromic deafness) or their absence (non-syndromic).6,7 The distributions of mutant gene expression are not necessarily restricted to clinically affected organ systems, and mutant genes associated with “non-syndromic” deafness may therefore have subtle extra-auditory manifestations. Genetic syndromes restricted to a cardio-auditory phenotype include the long QT syndrome (LQTS) caused by mutations in KvLQT1 ( KCNQ1 ) or in KCNE1 , where QT prolongation has autosomal dominant expression (Romano Ward syndrome), but congenital sensorineural hearing loss with LQTS is autosomal recessive (Jervell and Lange-Nielsen syndrome).8 In the LQTS, cardiac structure is normal. Recently, Schonberger et al …

Mutations of SLC26A4 cause Pendred syndrome, an autosomal recessive disorder comprising goitre and deafness with enlarged vestibular aqueducts (EVA). Recent studies in mouse models implicate Slc26a4 in the pathogenesis of asthma and hypertension. We hypothesise that asthma and hypertension are less prevalent among humans with SLC26A4 mutations.We reviewed medical histories and SLC26A4 genotypes for 80 individuals with EVA and 130 of their unaffected family members enrolled in a study of EVA. We used Fisher's exact test to compare the prevalence of asthma and hypertension among groups of subjects with zero, one, or two mutant alleles of SLC26A4.Although none of the 21 subjects with two mutant alleles of SLC26A4 had asthma or hypertension, there were no statistically significant differences in the prevalence of asthma or hypertension among subjects with zero, one, or two mutant alleles.There might be a protective effect of SLC26A4 mutations for asthma and hypertension but our study is statistically underpowered to detect this effect. Study sizes of at least 1125 and 504 individuals will be needed for 80% power to detect an effect at alpha = 0.05 for asthma and hypertension, respectively. Our hypothesis merits a larger study since it has implications for potential strategies to treat hearing loss by manipulating SLC26A4 expression or function.

Usher syndrome (USH) is an autosomal recessive disorder comprising of bilateral sensorineural hearing loss, progressive loss of vision due to retinitis pigmentosa (RP), and variable vestibular dysfunction. It is the most frequent cause of deafness and concurrent blindness in schools for the deaf-blind,1with a prevalence of 1/16 000 to 1/50 000 in various populations.2The majority of Usher syndrome cases can be clinically classified into three subtypes.3,4USH type I (USH1; OMIM 276900, 276903, 276904, 601067, 602097, 602083 and 606943) is characterised by profound prelingual sensorineural hearing loss, vestibular areflexia, and prepubertal onset of RP. USH type II (USH2; OMIM 276901, 276905 and 605472) is characterised by moderate to severe hearing impairment, no vestibular impairment, and onset of RP in the first or second decade of life. USH type III (USH3; OMIM 276902) is characterised by progressive, post-lingual hearing loss, variable onset and severity of RP, with or without vestibular dysfunction. Atypical forms of Usher syndrome associated with mutations in USH1B and USH1D have also been reported.5–7There is progression of hearing loss in some of these atypical cases, making them potentially difficult to clinically distinguish from USH3. USH3 was originally thought to be very rare, accounting for at most a few percent of the total USH population, until Pakarinen and coworkers found that up to 40% of the USH cases in Finland were consistent with USH3.4Difficulty in accurately detecting the progression of hearing loss may account for the lower frequency of reported USH3 cases outside of Finland. In the Finnish USH3 cohort, hearing loss was diagnosed before the age of 10 years in most patients, but up to the age of 40 years in some patients, with moderate to severe hearing threshold elevations at the time of detection. The mean …

Editor—Existing published data cannot conclusively determine if the M34T allele of connexin-26 ( GJB2 ) is a recessive allele causing hearing loss. The recent article by Houseman et al ( J Med Genet 2001; 38 :20-5) “Genetic analysis of the connexin-26 M34T variant: identification of genotype M34T/M34T segregating with mild-moderate non-syndromic sensorineural hearing loss,” does not resolve this question. Houseman et al state that M34T segregates with hearing loss, although their data are inconsistent with this assertion. GJB2 genotype data were available for five sib pairs, yet only two of the sib pairs (1 and 2) showed cosegregation of M34T with hearing loss. Sib pairs 3, 4, and 5 showed discordant inheritance of M34T with hearing loss, raising the likelihood that their hearing loss was unrelated to the GJB2 genotype. Biallelic GJB2 mutations and/or polymorphisms were detected only in sib pairs 1 (M34T/M34T) and 5 (M34T/35delG) and subject SP6A (M34T/35delG). It is unknown if a trans GJB2 mutation was missed in the other … Dr Kelsell, kelsell{at}icrf.icnet.uk