Relevance of the A1555G mutation in the 12S rRNA gene for hearing impairment in Austria.

OBJECTIVE: To analyze the prevalence and importance of the maternally inherited A1555G mutation in the 12S rRNA gene in the Austrian population. STUDY DESIGN: Investigation for mutations of genetically affected familial and sporadic cases of hearing impairment (HI), including analyses of audiometric data. SETTING: Teaching hospital, tertiary referral center. PATIENTS: Forty-five familial and 77 sporadic cases of nonsyndromic HI in an Austrian Caucasian ethnic group. MAIN OUTCOME MEASURE(S): Pure-tone audiometric data and screening by restriction fragment length polymorphism analysis after exclusion of GJB2 (Connexin 26) caused hearing loss. RESULTS: In the investigated hearing-impaired population, the mutation A1555G in the mitochondrial 12S rRNA gene was not detected. CONCLUSION: The A1555G mutation in the mitochondrial DNA 12S rRNA is not a major cause of HI in the Austrian Caucasian population.

GJB2 mutations in hearing impairment: identification of a broad clinical spectrum for improved genetic counseling.

OBJECTIVES/HYPOTHESIS: Hearing impairment has a high prevalence affecting approximately 1 in 1000 newborn children. Alterations in the gap junction protein beta 2 (GJB2) and gap junction protein beta 6 (GJB6) are associated with nonsyndromic hearing impairment and should have a significant impact on genetic counseling. STUDY DESIGN: Various cases of nonsyndromic hearing impairment were screened for alterations in GJB2 and GJB6 in this clinical study. METHODS: The prevalence of mutations in GJB2 encoding for connexin 26 in a patient group with nonsyndromic hearing impairment comprising 45 families and 57 sporadic cases was initially determined by sequencing. The role of GJB2 was then assessed in individuals with hearing impairment (3 families and 20 sporadic cases) who are usually excluded from analysis because of the presence of additional symptoms or in cases in which a role for nongenetic factors cannot be eliminated. In hearing-impaired individuals with heterozygous GJB2 mutations the recently identified 342-kb deletion truncating GJB6 called del(GJB6-D13S1830) as a digenetic component in hearing impairment was excluded by polymerase chain reaction. RESULTS: Autosomal recessively inherited GJB2 mutations induced hearing impairment in 25.5% of individuals in the nonsyndromic hearing impairment group. GJB2 alterations were also seen in 17.4% of individuals in whom additional symptoms or a role for nongenetic involvement could not be excluded. In all, 15 different alterations in GJB2 were detected, including the previously unknown 154G>C, 557C>T, and 682C>T mutations, and these were correlated to clinical parameters. CONCLUSION: Improved genetic counseling can be performed by screening for GJB2 alterations in patients with nonsyndromic hearing impairment including patients within groups for which a role for exogenetic factors cannot be excluded. Specific genetic counseling for GJB2-linked hearing impairment in heterozygotes will depend on future research.

Connexin 26 mutations in cases of sensorineural deafness in eastern Austria.

Mutations in the connexin 26 (Cx26) gene (GJB2) are associated with autosomal nonsyndromic sensorineural hearing loss. This study describes mutations in the Cx26 gene in cases of familial and sporadic hearing loss (HL) by gene sequencing and identifies the allelic frequency of the most common mutation leading to HL (35delG) in the population of eastern Austria. For this purpose we have developed and applied a molecular beacon based real-time mutation detection assay. Mutation frequencies in the Cx26 gene of individuals from affected families (14 out of 46) and sporadic cases (11 out of 40) were 30.4% and 27.5%, respectively. In addition to known disease related alterations, a novel mutation 262 G-->T (A88S) was also identified. 35delG accounted for almost 77% of all Cx26 mutations detected and displayed an allelic frequency in the normal hearing population of 1.7% (2 out of 120). The high prevalence of the 35delG mutation in eastern Austria would therefore allow screening of individuals and family members with Cx26 dependent deafness by a highly specific and semi-automated method.

Screening for monogenetic del(GJB6-D13S1830) and digenic del(GJB6-D13S1830)/GJB2 patterns of inheritance in deaf individuals from Eastern Austria.

Genetically caused congenital deafness is a common trait affecting 1 in 2000 newborn children and is predominantly inherited in an autosomal recessive fashion. Genes such as the gap junction protein beta 2 (GJB2) encoding for Connexin (Cx26) and GJB6 (Cx30) are known to cause sensorineural deafness. Autosomal recessive deafness has been linked both to the monogenetic occurrence of mutated GJB2 or the GJB6 deletion del(GJB6-D13S1830) and digenic GJB2/del(GJB6-D13S1830) inheritance. Monogenetic GJB2 alterations are responsible for 25.5% of deafness in the eastern Austrian population. An additional 9.8% are heterozygous carriers of a single GJB2 mutation which is not responsible for deafness alone. Del(GJB6-D13S1830) and GJB2/del(GJB6-D13S1830) mutations have been shown to be the second most frequent cause of deafness in different populations. To address the question of the relevance of mutations in GJB6 either as a monogenetic or a digenic GJB2/del(GJB6-D13S1830) cause of deafness in this population, 76 unrelated individuals (33 families and 43 sporadic cases) were screened using PCR strategies. Similar to studies in other hard of hearing populations with similar or lower carrier frequencies of single GJB2 mutations, the presence of del(GJB6-D13S1830) was not detected in any individual within the patient group. Data therefore exclude a digenetic association of del(GJB6-D13S1830) with heterozygous GJB2 mutations as a cause of deafness in a representative sample of the population from Eastern Austria.

Lack of association between Connexin 31 (GJB3) alterations and sensorineural deafness in Austria.

Mutations in the gap junction protein beta 3 (GJB3) gene encoding Connexin 31 (Cx31) are known to cause autosomal inherited sensorineural deafness, erythrokeratodermia and neuropathy. The role of Cx31 mutations has not been described in familial cases of non-syndromic hearing impairment (NSHI) in central European populations. To identify mutations in the Austrian population, highly selected familial (n=24) and sporadic (n=21) cases of isolated NSHI were screened by analysis of the complete coding sequence of Cx31, after exclusion of a common Cx26 causing deafness. Three different variations occurring in a total of 37% of all cases were identified. A C94T (R32W) missense mutation was seen in 4.4% of cases and two silent alterations C357T and C798T were detected in 8.9% and 24.4% of cases exclusively in a heterozygous pattern. No correlation between Cx31 alterations and deafness was found. To investigate the role of heterozygous Cx31 variations for a possibly combination allelic disease inheritance with Cx26 mutations as shown for Connexin 30 and Connexin 26, patients with Cx26 variations were tested. Our data suggest that Cx31 alterations are common but have no or a low genetic relevance in the Austrian hearing impaired population with or without Cx26 alterations.

High incidence of GJB2 mutations during screening of newborns for hearing loss in Austria.

OBJECTIVES: The aim of the present study was to evaluate gap junction protein beta2 (GJB2) genetic testing within a national neonate screening program for hearing loss (HL) in a European population. DESIGN: Neonatal cases of nonsyndromic HL (N = 21) were identified by postpartal otoacoustic emissions (OAE) and brain stem electric response audiometry (BERA) analysis. GJB2 testing was performed by direct sequencing. RESULTS: Mutations in GJB2 were found in 15 of 21 children (71.4%) identified by neonatal audiological screening. The 35delG mutation in GJB2 was found homozygous in 10 cases (47.6%) and also as a clear cause of HL as the heterozygous alterations 35delG/del311-324 and 35delG/L90P. In a single case, L90P/R143Q was also identified as a cause of HL. In 3 HL cases that were not identifiable during initial OAE testing, homozygous 35delG and 35delG/R184P defined the genetic basis for HL in 2 cases, whereas one case had wild-type GJB2. CONCLUSIONS: Our findings of the high mutation rate in the Austrian population, especially in neonates identified during the newborn screening program, confirm the importance of screening for mutations in GJB2.

Relevance of the A1555G Mutation in the 12S rRNA Gene for Hearing Impairment in Austria.

OBJECTIVE:: To analyze the prevalence and importance of the maternally inherited A1555G mutation in the 12S rRNA gene in the Austrian population. STUDY DESIGN:: Investigation for mutations of genetically affected familial and sporadic cases of hearing impairment (HI), including analyses of audiometric data. SETTING:: Teaching hospital, tertiary referral center. PATIENTS:: Forty-five familial and 77 sporadic cases of nonsyndromic HI in an Austrian Caucasian ethnic group. MAIN OUTCOME MEASURE(S):: Pure-tone audiometric data and screening by restriction fragment length polymorphism analysis after exclusion of GJB2 (Connexin 26) caused hearing loss. RESULTS:: In the investigated hearing-impaired population, the mutation A1555G in the mitochondrial 12S rRNA gene was not detected. CONCLUSION:: The A1555G mutation in the mitochondrial DNA 12S rRNA is not a major cause of HI in the Austrian Caucasian population.

A novel connexin 26 mutation associated with autosomal recessive sensorineural deafness.

Mutations in the connexin 26 (Cx26) gene (GJB2) are a common cause of hereditary hearing impairment which affects approximately 1 in 2000 newborn children. We report the identification of a novel Cx26 point mutation (439 G-->A) linked to familial, autosomal recessive, sensorineural hearing loss. This missense mutation (E147K) is located in the highly conserved, putative K(+) channel lining sequence of the third transmembrane domain (TM3) of Cx26. Hearing impairment associated with this mutation was congenital, moderate to profound and showed no signs of progressive deterioration.