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.

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.

Present addresses of 12,752 like-sexed twin pairs born in the period 1915-1960 were identified. A questionnaire, concerning the similarity of pair members, was sent to all individuals. Responses were obtained from 83.7% of the subjects. The zygosity of 207 pairs was established by examination of genetic markers. By using discriminant analysis on the responses from this subgroup, functions were obtained for prediction of zygosity from questionnaire data. It was estimated that 2.4% of the pairs would be misclassified if the questionnaire responses from both pair members were used, and 3.9% if only the response from one of the twins was used. Accordingly, zygosity could be predicted with satisfactory reliability also for twin pairs where only one of the twins had responded. The predicted percentage of monozygotic (MZ) pairs among pairs where one or both twins had responded, was 39.4 (4,402/11,175). The percentage of MZ pairs was significantly lower (34.5) in death-discordant pairs than in pairs in which both twins were alive (39.6). The zygosity questionnaire data are sufficient to adequately score twin pairs for zygosity in the great majority of cases.

We ascertained a large North American family, LMG309, with matrilineal transmission of non‐syndromic, progressive sensorineural hearing loss (SNHL). There was no history of aminoglycoside exposure, and penetrance was complete. We sequenced the entire mitochondrial genome and identified the previously reported 7510T>C transition in the tRNASer(UCN) gene. The 7510T>C was homoplasmic in all affected members. The LMG309 mitochondrial sequence belongs to an unnamed subgroup of mitochondrial haplogroup H. We demonstrate that the previously reported Spanish family S258 carries 7510T>C on a different mitochondrial sub‐haplogroup, H1. We did not detect 7510T>C among 79 Caucasian haplogroup H control samples, including 11 from sub‐haplogroup H1 and one from the same sub‐haplogroup as LMG309. Our results provide strong genetic evidence that 7510T>C is a pathogenic mutation that causes non‐syndromic SNHL.

BACKGROUND:Non-syndromic hearing loss is among the most genetically heterogeneous traits known in humans. To date, at least 50 loci for autosomal dominant non-syndromic sensorineural hearing loss (ADNSSHL) have been identified by linkage analysis.OBJECTIVE:To report the mapping of a novel autosomal dominant deafness locus on the long arm of chromosome 14 at 14q11.2-q12, DFNA53, in a large multigenerational Chinese family with post-lingual, high frequency hearing loss that progresses to involve all frequencies.RESULTS:A maximum multipoint LOD score of 5.4 was obtained for marker D14S1280. The analysis of recombinant haplotypes mapped DFNA53 to a 9.6 cM region interval between markers D14S581 and D14S1021. Four deafness loci (DFNA9, DFNA23, DFNB5, and DFNB35) have previously been mapped to the long arm of chromosome 14. The critical region for DFNA53 contains the gene for DFNA9 but does not overlap with the regions for DFNB5, DFNA23, or DFNB35. Screening of the COCH gene (DFNA9), BOCT, EFS, and HSPC156 within the DFNA53 interval did not identify the cause for deafness in this family.CONCLUSIONS:Identifying the DFNA53 locus is the first step in isolating the gene responsible for hearing loss in this large multigeneration Chinese family.

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 …

Objective: To test the accuracy of bilateral language mapping using a standard clinical magnetic resonance (MR) imaging device during word generation. Design. A study of normal volunteers. Setting. Volunteers from the Washington, DC, area. Participants. Nine normal, right-handed, native English speakers (four women, five men, mean age 31 years). Interventions. During four MR acquisition periods, subjects would alternately rest and silently generate words. Sagittal MR images covered the middle and inferior frontal gyri, insulae, and part of the temporal and parietal lobes bilaterally. Main outcome measures. (1) Anatomic maps of task-related signal changes obtained by comparing, in each voxel, the signal during word generation and rest periods, and (2) analysis of the time course of the signal. Results. Maximum responses were in the left hemisphere, mainly in the frontal lobe (Broca9s area, premotor cortex, and dorsolateral prefrontal cortex) but also in posterior regions such as Wernicke9s area. In agreement with previous studies, some degree of task-related changes was present in a subset of the corresponding regions in the right hemisphere. Conclusion. Despite certain limitations, it is possible, using widely available MR equipment, to obtain results consistent with previous studies. The technique may have important implications for assessment of cognitive functions in patients with neurologic disorders in a clinical environment. NEUROLOGY 1995;45: 1821-1827

Objective: The aim of the present study was to characterize audiological profiles in patients with GJB2 deafness Design: We screened DNA from 399 individuals with nonsyndromic deafness for mutations in the connexin 26 gene (GJB2) by sequence analysis. A total of 77 (19%) of these deaf individuals were biallelic GJB2 mutations (either homozygous or compound heterozygous mutations) (GJB2 deafness). Using the audiological classification criteria of genetic deafness proposed by the European Workshop on Genetic Hearing Loss, we analyzed audiograms of these patients to characterize audiological features of the GJB2 deafness. In addition, we reviewed audiological data of 411 deafness cases from the literature providing details of audiological data (including 157 with GJB2 deafness). Results: All categories of hearing loss severity were found, with significant differences in the findings from GJB2 cases: 1 (4.5%) of 22 individuals with mild hearing loss, 10 (13.3%) of 75 with moderate loss, 14 (14.9%) of 94 with severe loss, and 52 (25%) of 208 with profound deafness (Chi-square test, 3 df, p = 0.016). 81.6% of patients with GJB2 mutations had severe to profound loss, 18.4% with mild to moderate loss (Chi-square test, p = 0.014). The 235delC mutation was always associated with profound deafness. The main audiogram shapes found were residual/sloping (72.7%) and flat (23.4%). There were no differences in the severity and audiogram shapes of the hearing impairment between homozygous and compound heterozygous GJB2 deafness (Chi-square test, p > 0.05). Conclusions: Our study shows that the probability of finding biallelic GJB2 mutations increases with the severity of hearing loss. Audiograms associated with GJB2 deafness were usually nonspecific. Patients with unknown causes of severe or profound hearing loss should be routinely tested for GJB2 mutations, but due to the variability in hearing loss, individuals with lesser degrees of hearing loss should not be precluded from testing.

The connexins are the subunits of a family of proteins that form gap junctions, allowing ions and small molecules to move between adjacent cells. At least four connexins are expressed in the ear, and, although there are known mutations at >100 loci that can cause deafness, those involving DFNB1, in the interval 13q11-q12 containing the GJB2 and GJB6 genes coding for connexins 26 and 30, are the most frequent cause of recessive deafness in many populations. We have suggested that the combined effects of relaxed selection and linguistic homogamy can explain the high frequency of connexin deafness and may have doubled its incidence in this country during the past 200 years. In this report, we show by computer simulation that assortative mating, in fact, can accelerate dramatically the genetic response to relaxed selection. Along with the effects of gene drift and consanguinity, assortative mating also may have played a key role in the joint evolution and accelerated fixation of genes for speech after they first appeared in Homo sapiens 100,000-150,000 years ago.

Recessive mutations of SLC26A4 (PDS) are a common cause of Pendred syndrome and non-syndromic deafness in western populations. Although south and east Asia contain nearly one half of the global population, the origins and frequencies of SLC26A4 mutations in these regions are unknown. We PCR amplified and sequenced seven exons of SLC26A4 to detect selected mutations in 274 deaf probands from Korea, China, and Mongolia. A total of nine different mutations of SLC26A4 were detected among 15 (5.5%) of the 274 probands. Five mutations were novel and the other four had seldom, if ever, been identified outside east Asia. To identify mutations in south Asians, 212 Pakistani and 106 Indian families with three or more affected offspring of consanguineous matings were analysed for cosegregation of recessive deafness with short tandem repeat markers linked to SLC26A4. All 21 SLC26A4 exons were PCR amplified and sequenced in families segregating SLC26A4 linked deafness. Eleven mutant alleles of SLC26A4 were identified among 17 (5.4%) of the 318 families, and all 11 alleles were novel. SLC26A4 linked haplotypes on chromosomes with recurrent mutations were consistent with founder effects. Our observation of a diverse allelic series unique to each ethnic group indicates that mutational events at SLC26A4 are common and account for approximately 5% of recessive deafness in south Asians and other populations.

Editor—Congenital deafness occurs in approximately 1 in 1000 live births and 50% of these cases are hereditary. Non-syndromic deafness is classified according to its mode of inheritance as DFN, DFNA, and DFNB (X linked, autosomal dominant, and autosomal recessive, respectively). Non-syndromic recessive deafness accounts for ∼80% of congenital hereditary deafness cases.1 At least 30 DFNB loci have been mapped in the past few years by genetic linkage studies, but the causative gene has been identified for only eight of these loci2-4 (Hereditary Hearing Loss Homepage, http://www.uia.ac.be/dnalab/hhh). Two of the previously reported loci for non-syndromic recessive deafness are DFNB8 and DFNB10, both located on chromosome 21q22.3 (MIM 601072 and 605316). The DFNB8 locus was originally identified in a large consanguineous Pakistani family, segregating childhood onset deafness,5 while DFNB10 was identified in a large consanguineous Palestinian family, in which deafness was congenital.6 Recently, the TMPRSS3 gene was shown to be mutated in affected subjects of both families.7 TMPRSS3 belongs to a family of transmembrane serine proteases, also including TMPRSS1,8 TMPRSS2,9 and TMPRSS4.10 The TMPRSS3 gene extends over 24 kb and comprises 13 exons. It has four alternative transcripts ( TMPRSS3 a , b , c , and d ), encoding putative peptides of 454, 327, 327, and 344 amino acids, respectively.7 TMPRSS3a , which contains all 13 exons, is the most abundant transcript and its expression could be detected in various tissues, including fetal cochlea.7 In addition to the serine protease and the transmembrane domains, TMPRSS3 also encodes low density lipoprotein receptor class A (LDLRA) and scavenger receptor cysteine rich (SRCR) domains, which are potentially involved in binding with extracellular molecules and/or the cell surface.7 To identify DFNB8/B10 linked families, we analysed a total of 159 consanguineous Pakistani families that …

Genes causing nonsyndromic autosomal recessive deafness (DFNB12) and deafness associated with retinitis pigmentosa and vestibular dysfunction (USH1D) were previously mapped to overlapping regions of chromosome 10q21-q22. Seven highly consanguineous families segregating nonsyndromic autosomal recessive deafness were analyzed to refine the DFNB12 locus. In a single family, a critical region was defined between D10S1694 and D10S1737, approximately 0.55 cM apart. Eighteen candidate genes in the region were sequenced. Mutations in a novel cadherin-like gene, CDH23, were found both in families with DFNB12 and in families with USH1D. Six missense mutations were found in five families with DFNB12, and two nonsense and two frameshift mutations were found in four families with USH1D. A northern blot analysis of CDH23 showed a 9.5-kb transcript expressed primarily in the retina. CDH23 is also expressed in the cochlea, as is demonstrated by polymerase chain reaction amplification from cochlear cDNA.

Recessive mutations at Cx 26 are known to be the cause of nearly half of all genetic deafness in many populations. Since assortative mating is known to increase the variance of continuous traits and the frequency of qualitative genetic phenotypes (such as recessive deafness), it seems possible that the high frequency of Cx 26 deafness may be related to the mating structure of the deaf population. During the past 200 years, improvements in educational, social and economic circumstances have lead to an increase in the fertility of the deaf along with the appearance of assortative mating in many western populations including the United States. The new deaf by deaf mating pool has increased the frequency of common forms of recessive deafness such as Cx 26 because the non-complementary matings which produce many of the deaf offspring from these marriages are proportional to the fourth power of the gene frequency. Existing data on the frequency of non-complementary marriages among the deaf in the 19 th century suggest that the incidence of Cx 26 deafness has increased in the past 100 years along with the proportion of deaf children bom to deaf parents. Current observations also suggest that the high frequency of Cx 26 deafness may be confined to populations with a long tradition of intermarriage among the deaf. In Japan, for example, Fuse et al (Neuro report 10:1853, 1999) found Cx 26 deafness in only four of 20 multiplex sibships (20%). The comparable rate for multiplex probands in the U.S. is 49% (Green et al, JAMA 281:2211, 1999). Although we are not aware of data on the frequency of deaf by deaf matings in Japan, they were virtually unheard of in India in the past, and accounted for only about 1% of the marriages of the deaf in a reported survey from China (Liu et al, Chinese Med Genet 5:193, 1988). All of these findings are consistent with the hypothesis that variation in the mating structure may have contributed to differences in the current distribution of this trait throughout the world.

Profound hearing loss has an incidence of 1:1000 children, and is genetically determined in at least half of the cases. The GJB2 gene encoding the gap junction protein 2, also called Connexin 26, is one of a growing number of genes found to have mutations which can result in hearing loss. One particular GJB2 mutation, 35delG accounts for 50-80% of recessive deafness in the Caucasian population of European descent. A second mutation, 167delT has a high prevalence in the Ashkenazi Jewish population with a carrier frequency of about 4%. At least 40 other GJB2 alleles associated with hearing loss have been reported. There is significant phenotypic variability both in the severity and progression of hearing impairment. This, coupled with the relative ease of testing for mutations at this locus, has raised important ethical and social issues when counseling deaf probands and their families. To address these issues and to obtain more accurate estimates of the frequency of different mutations at the GJB2 locus in the US population, we ascertained deaf probands from both multiplex and simplex families through a national survey conducted by the Research Institute at Gallaudet University, as well as from the student body at Gallaudet University. Molecular analysis was performed by direct fluorescent sequencing of the coding region of the GJB2 locus. So far, we have observed five previously described and two new mutations. An Arg32Cys substitution at a highly conserved residue in the first transmembrane domain was observed in a compound heterozygote with congenital deafness. We also found a novel nonsense mutation at codon 136 in a compound heterozygote. Connexin deafness accounted for 24% of the 92 US probands, and 79% of the mutant alleles were 35delG. Analysis of audiometric data on more than half of these probands is presented with comparison to previous studies. Identification of the mutational spectrum at this locus will allow a careful genotype-phenotype correlation and provide more accurate estimates of the frequencies of various GJB2 alleles. This will enable provision of accurate diagnosis, prognosis and counseling for appropriate language and speech development as well as for future recurrence risk.

A large Filipino-American family with progressive matrilineal hearing loss, premature graying, depigmented patches, and digital anomalies was ascertained through a survey of a spina bifida clinic for neural crest disorders. Deafness followed a matrilineal pattern of inheritance and was associated with the A1555G mutation in the 12S rRNA gene (MTRNR1) in affected individuals as well as unaffected maternal relatives. Several other malformations were found in carriers of the mutation. The proband had a myelocystocele, Arnold-Chiari type I malformation, cloacal exstrophy, and severe early-onset hearing loss. Several family members had premature graying, white forelock, congenital leukoderma with or without telecanthus, somewhat suggestive of a Waardenburg syndrome variant. In addition to the patient with myelocystocele, two individuals had scoliosis and one had segmentation defects of spinal vertebrae. The syndromic characteristics reported here are novel for the mitochondrial A1555G substitution, and may result from dysfunction of mitochondrial genes during early development. However, the mitochondrial A1555G mutation is only rarely associated with neural tube defects as it was not found in a screen of 218 additional individuals with spina bifida, four of whom had congenital hearing loss.

Biotinidase deficiency is characterized by neurological and cutaneous abnormalities that can be prevented or ameliorated by oral biotin therapy. A child with biotinidase deficiency went undiagnosed for a long period and has irreversible neurological deficits despite biotin treatment. This child is homozygous for the most common mutation (G98:d7i3) found in symptomatic children with the disorder. The parents insisted on having prenatal diagnosis in a subsequent pregnancy to alleviate their anxiety about having another affected child. Mutation analysis of DNA obtained directly from amniotic fluid and from cultured amniocytes revealed that the fetus was heterozygous for the mutation. Maternal cell contamination of the amniocytes was excluded by genotype analysis. Biotinidase activity in extracts of cultured amniocytes revealed 40 per cent of mean normal activity. At birth, the infant was confirmed to be heterozygous by serum enzyme analysis. This is the first report of the use of molecular analysis for the prenatal diagnosis for biotinidase deficiency.

Preimplantation genetic testing (PGT) on embryos from couples at risk for Huntington disease can achieve disease prevention in offspring without disclosure of parental genotype. This strategy may also be applicable to other extremely deleterious dominant traits.