Genomic copy number alterations in non-syndromic hearing loss.

Genetic heterogeneity has made the identification of genes related to hearing impairment a challenge. In the absence of a clear phenotypic aetiology, recurrence risk estimates are often based on family segregation and may be imprecise. We profiled by oligonucleotide array-CGH patients presenting non-syndromic hearing loss with presumptive autosomal recessive (n = 50) or autosomal dominant (n = 50) patterns of inheritance. Rare copy number variants (CNVs) were detected in 12 probands; four of the detected CNVs comprised genes previously associated with hearing loss (POU4F3, EYA4, USH2A, and BCAP31) and were considered causative, stressing the contribution of genomic imbalance to non-syndromic deafness. In six cases, segregation of the CNVs in pedigrees excluded them as causative. In one case, segregation could not be investigated, while in another case, a point mutation likely explains the phenotype. These findings show that the presumptive patterns of inheritance were incorrect in at least two cases, thereby impacting genetic counselling. In addition, we report the first duplication reciprocal to the rare ABCD1, BCAP31, and SLC6A8 contiguous deletion syndrome; as with most microduplication syndromes, the associated phenotype is much milder than the respective microdeletion and, in this case, was restricted to hearing impairment.

Cochlea cell-specific marker expression upon in vitro Hes1 knockdown.

NOTCH pathway proteins, including the transcriptional factor HES1, play crucial roles in the development of the inner ear by means of the lateral inhibition mechanism, in which supporting cells have their phenotype preserved while they are prevented from becoming hair cells. Genetic manipulation of this pathway has been demonstrated to increase hair cell number. The present study aimed to investigate gene expression effects in hair cells and supporting cells after Hes1-shRNA lentivirus transduction in organotypic cultures of the organ of Corti from postnatal-day-3 mice. Forty-eight hours after in vitro knockdown, Hes1 gene expression was reduced at both mRNA and protein levels. Myo7a (hair cell marker) and Sox2 (progenitor cell marker) mRNA levels also significantly increased. The modulation of gene expression in the organ of Corti upon Hes1 knockdown is consistent with cell phenotypes related to lateral inhibition mechanism interference in the inner ear. The lentivirus-based expression of Hes1-shRNA is a valuable strategy for genetic interference in the organ of Corti and for future evaluation of its efficacy in protocols aiming at the regeneration of hair cells in vivo.

Chromosome imbalances in syndromic hearing loss.

The cause of hearing impairment has not been elucidated in a large proportion of patients. We screened by 1-Mb array-based comparative genomic hybridization (aCGH) 29 individuals with syndromic hearing impairment whose clinical features were not typical of known disorders. Rare chromosomal copy number changes were detected in eight patients, four de novo imbalances and four inherited from a normal parent. The de novo alterations define candidate chromosome segments likely to harbor dosage-sensitive genes related to hearing impairment, namely 1q23.3-q25.2, 2q22q23, 6p25.3 and 11q13.2-q13.4. The rare imbalances also present in normal parents might be casually associated with hearing impairment, but its role as a predisposition gene remains a possibility. Our results show that syndromic deafness is frequently associated with chromosome microimbalances (14-27%), and the use of aCGH for defining disease etiology is recommended.

Whole-genome array-CGH screening in undiagnosed syndromic patients: old syndromes revisited and new alterations.

We report array-CGH screening of 95 syndromic patients with normal G-banded karyotypes and at least one of the following features: mental retardation, heart defects, deafness, obesity, craniofacial dysmorphisms or urogenital tract malformations. Chromosome imbalances not previously detected in normal controls were found in 30 patients (31%) and at least 16 of them (17%) seem to be causally related to the abnormal phenotypes. Eight of the causative imbalances had not been described previously and pointed to new chromosome regions and candidate genes for specific phenotypes, including a connective tissue disease locus on 2p16.3, another for obesity on 7q22.1-->q22.3, and a candidate gene for the 3q29 deletion syndrome manifestations. The other causative alterations had already been associated with well-defined phenotypes including Sotos syndrome, and the 1p36 and 22q11.21 microdeletion syndromes. However, the clinical features of these latter patients were either not typical or specific enough to allow diagnosis before detection of chromosome imbalances. For instance, three patients with overlapping deletions in 22q11.21 were ascertained through entirely different clinical features, i.e., heart defect, utero-vaginal aplasia, and mental retardation associated with psychotic disease. Our results demonstrate that ascertainment through whole-genome screening of syndromic patients by array-CGH leads not only to the description of new syndromes, but also to the recognition of a broader spectrum of features for already described syndromes. Furthermore, on the technical side, we have significantly reduced the amount of reagents used and costs involved in the array-CGH protocol, without evident reduction in efficiency, bringing the method more within reach of centers with limited budgets.

Prevalence of the A1555G (12S rRNA) and tRNASer(UCN) mitochondrial mutations in hearing-impaired Brazilian patients.

Mitochondrial mutations are responsible for at least 1% of the cases of hereditary deafness, but the contribution of each mutation has not yet been defined in African-derived or native American genetic backgrounds. A total of 203 unselected hearing-impaired patients were screened for the presence of the mitochondrial mutation A1555G in the 12S rRNA gene and mutations in the tRNASer(UCN) gene in order to assess their frequency in the ethnically admixed Brazilian population. We found four individuals with A1555G mutation (2%), which is a frequency similar to those reported for European-derived populations in unselected samples. On the other hand, complete sequencing of the tRNASer(UCN) did not reveal reported pathogenic substitutions, namely A7445G, 7472insC, T7510C, or T7511C. Instead, other rare substitutions were found such as T1291C, A7569G, and G7444A. To evaluate the significance of these findings, 110 "European-Brazilians" and 190 "African-Brazilians" unrelated hearing controls were screened. The T1291C, A7569G and G7444A substitutions were each found in about 1% (2/190) of individuals of African ancestry, suggesting that they are probably polymorphic. Our results indicate that screening for the A1555G mutation is recommended among all Brazilian deaf patients, while testing for mutations in the tRNASer(UCN) gene should be considered only when other frequent deafness-causing mutations have been excluded or in the presence of a maternal transmission pattern.

Transplantation and survival of mouse inner ear progenitor/stem cells in the organ of Corti after cochleostomy of hearing-impaired guinea pigs: preliminary results.

In mammals, damage to sensory receptor cells (hair cells) of the inner ear results in permanent sensorineural hearing loss. Here, we investigated whether postnatal mouse inner ear progenitor/stem cells (mIESCs) are viable after transplantation into the basal turns of neomycin-injured guinea pig cochleas. We also examined the effects of mIESC transplantation on auditory functions. Eight adult female Cavia porcellus guinea pigs (250-350 g) were deafened by intratympanic neomycin delivery. After 7 days, the animals were randomly divided in two groups. The study group (n=4) received transplantation of LacZ-positive mIESCs in culture medium into the scala tympani. The control group (n=4) received culture medium only. At 2 weeks after transplantation, functional analyses were performed by auditory brainstem response measurement, and the animals were sacrificed. The presence of mIESCs was evaluated by immunohistochemistry of sections of the cochlea from the study group. Non-parametric tests were used for statistical analysis of the data. Intratympanic neomycin delivery damaged hair cells and increased auditory thresholds prior to cell transplantation. There were no significant differences between auditory brainstem thresholds before and after transplantation in individual guinea pigs. Some mIESCs were observed in all scalae of the basal turns of the injured cochleas, and a proportion of these cells expressed the hair cell marker myosin VIIa. Some transplanted mIESCs engrafted in the cochlear basilar membrane. Our study demonstrates that transplanted cells survived and engrafted in the organ of Corti after cochleostomy.

Cochlea cell-specific marker expression upon in vitro Hes1 knockdown

NOTCH pathway proteins, including the transcriptional factor HES1, play crucial roles in the development of the inner ear by means of the lateral inhibition mechanism, in which supporting cells have their phenotype preserved while they are prevented from becoming hair cells. Genetic manipulation of this pathway has been demonstrated to increase hair cell number. The present study aimed to investigate gene expression effects in hair cells and supporting cells after Hes1-shRNA lentivirus transduction in organotypic cultures of the organ of Corti from postnatal-day-3 mice. Forty-eight hours after in vitro knockdown, Hes1 gene expression was reduced at both mRNA and protein levels. Myo7a (hair cell marker) and Sox2 (progenitor cell marker) mRNA levels also significantly increased. The modulation of gene expression in the organ of Corti upon Hes1 knockdown is consistent with cell phenotypes related to lateral inhibition mechanism interference in the inner ear. The lentivirus-based expression of Hes1-shRNA is a valuable strategy for genetic interference in the organ of Corti and for future evaluation of its efficacy in protocols aiming at the regeneration of hair cells in vivo.

Relationship of expansion of CGG repeats and X-inactivation with expression of fra(X)(q27.3) in heterozygotes.

Expression of the fragile site Xq27.3 was investigated in 82 heterozygotes (58 normal and 24 mentally impaired) diagnosed by DNA analysis. EcoRI and EagI DNA digests were probed with StB12.3. This allowed the detection of the expansion of the CGG repeat of the FMR1 gene and the methylation pattern of the adjacent CpG island. Heterozygotes with delta < or = 400 bp (52/82) were all mentally normal and manifested fra(X) in less than 3% of the cells or did not express it. Unmethylated mutant alleles were always observed. About two thirds of females with delta > 500 bp (21/30) showed fra(X) frequencies above 3% (3 normal and 18 mentally impaired). Lower frequencies of fra(X) or negative results were observed in the remaining 9 females (3 normal and 6 affected). The large mutant alleles were always methylated. Therefore, while delta < or = 400 bp is always associated with negative or low expression of fra(X), larger expansions are not present exclusively in heterozygotes with high frequencies of fra(X). In 25 of 30 heterozygotes with delta > 500 bp, active and inactive normal alleles were observed. Three fra(X)-negative or low manifesting heterozygotes showed completely skewed X-inactivation, with the normal allele either active or inactive. Two females with high frequencies of fra(X) always had the normal allele inactivated. Densitometry studies showed no difference in the inactivation of the normal allele between heterozygotes who manifested fra(X) or not. Thus fra(X) expression does not seem to be influenced by X-inactivation.

The number of CGG repeats of the FMR1 locus in premutated and fully mutated heterozygotes and their offspring: implications for the origin of mosaicism.

The size of the CGG repeat of the FMR1 gene was investigated with probe StB12.3 in 154 transmissions to the offspring of heterozygotes for the premutation and the full mutation. Among the 135 offspring of premutated heterozygotes there were three decreases in size of the repeats: in two of these cases a full mutation was present along with the decreased premutation, and in a third mosaic (46,fra(X)(q27.3),Y), a normal allele was observed. In the 19 offspring of fully mutated females with no detected mosaicism, there were three mosaics and three individuals who had full mutations that included a number of repeats smaller than those present in their mothers. Among the 32 offspring who received a premutation from their premutated mothers, 27 alleles were increased in size and 5 remained unaltered. Among 11 mosaic offspring of premutated mothers, the premutation increased in 4, decreased in 3, and was unchanged in 4. In contrast to the trend of an increasing premutation size in the non-mosaic offspring, the premutation present in mosaics can be smaller, larger, or of unaltered size with approximately equal frequencies. These data suggest that the premutations present in mosaics result from mitotic instability of the inherited full mutations. This is further supported by the finding of a mosaic male with a normal sized allele.

Fragile X frequency in a mentally retarded population in Brazil.

Seventy-five male and 50 female students from 2 special schools for mildly, moderately retarded, or borderline individuals were screened clinically and cytogenetically in order to estimate the contribution of fragile X [fra(X)] syndrome to the cause of mental retardation in Brazil. We found 6 males (8%) from 4 families and 2 unrelated females (4%) with fra(X) chromosomes. One male and one female were isolated cases. The estimated frequency of Martin-Bell [fra(X)] syndrome among mentally impaired individuals in Brazil was similar to that previously reported in other countries.

DXS548/FRAXAC1 haplotypes in fragile X chromosomes in the Brazilian population.

In order to investigate the origin of the fragile X mutation in the Brazilian population, we assessed the size of the microsatellite markers DXS548, FRAXAC1 and FRAXAC2 in 72 X chromosomes from unrelated affected males and 64 control chromosomes. We found a significantly different distribution of alleles between fragile X and controls for loci DXS548 and FRAXAC1, but no apparent linkage disequilibrium was detected for the sequence FRAXAC2. The most frequent DXS548/FRAXAC1 haplotypes in affected males were haplotypes 204/158 bp (2-1) and 196/152 bp (6-4). These findings are in accordance with the proposed two main mutational pathways for the generation of FMR-1 alleles that predispose to instability and hyperexpansion.

Fully mutated and gray-zone FRAXA alleles in Brazilian mentally retarded boys.

We used a non-isotopic polymerase chain reaction (PCR) technique for fragile X syndrome diagnosis to screen 256 mentally retarded boys who were selected randomly from special schools. Patients identified as pre- or full-mutation carriers were further investigated by Southern blot analysis with the StB12.3 probe. The PCR-based test identified five boys with the expanded allele and 17 other patients as carriers of either premutated or gray-zone alleles. The full mutation was confirmed in four cases after Southern blotting and a fifth patient carried a normal allele. Of the 17 patients identified with a premutation allele by PCR, one individual was diagnosed as mosaic by Southern blotting, 12 individuals displayed fragments of 2.90 kb or 2.85 kb, and the remaining four individuals showed apparently normal-sized fragments. However, sizing of these 16 alleles by further PCR analysis showed them to be in the gray-zone range (40-60 repeats). Therefore, the frequency of the full mutation in this cohort of mentally retarded boys was close to 2% (5/256). The prevalence of gray-zone alleles among those mentally impaired boys who did not carry the full mutation was 6.4% (16/251) and, although more than twice the prevalence of these alleles among a cohort of unaffected Brazilian males 2.8% (71251), the difference did not reach statistical significance.

Fragile X premutation is a significant risk factor for premature ovarian failure: the International Collaborative POF in Fragile X study--preliminary data.

The preliminary results of an international collaborative study examining premature menopause in fragile X carriers are presented. A total of 760 women from fragile X families was surveyed about their fragile X carrier status and their menstrual and reproductive histories. Among the subjects, 395 carried a premutation, 128 carried a full mutation, and 237 were noncarriers. Sixty-three (16%) of the premutation carriers had experienced menopause prior to the age of 40 compared with none of the full mutation carriers and one (0.4%) of the controls. Based on these preliminary data, there is a significant association between fragile X premutation carrier status and premature menopause.

Multilocus family-based association analysis of seven candidate polymorphisms with essential hypertension in an african-derived semi-isolated brazilian population.

Background. It has been widely suggested that analyses considering multilocus effects would be crucial to characterize the relationship between gene variability and essential hypertension (EH). Objective. To test for the presence of multilocus effects between/among seven polymorphisms (six genes) on blood pressure-related traits in African-derived semi-isolated Brazilian populations (quilombos). Methods. Analyses were carried out using a family-based design in a sample of 652 participants (97 families). Seven variants were investigated: ACE (rs1799752), AGT (rs669), ADD2 (rs3755351), NOS3 (rs1799983), GNB3 (rs5441 and rs5443), and GRK4 (rs1801058). Sensitivity analyses were further performed under a case-control design with unrelated participants only. Results. None of the investigated variants were associated individually with both systolic and diastolic BP levels (SBP and DBP, respectively) or EH (as a binary outcome). Multifactor dimensionality reduction-based techniques revealed a marginal association of the combined effect of both GNB3 variants on DBP levels in a family-based design (P = 0.040), whereas a putative NOS3-GRK4 interaction also in relation to DBP levels was observed in the case-control design only (P = 0.004). Conclusion. Our results provide limited support for the hypothesis of multilocus effects between/among the studied variants on blood pressure in quilombos. Further larger studies are needed to validate our findings.

Transplantation and survival of mouse inner ear progenitor/stem cells in the organ of Corti after cochleostomy of hearing-impaired guinea pigs: preliminary results

In mammals, damage to sensory receptor cells (hair cells) of the inner ear results in permanent sensorineural hearing loss. Here, we investigated whether postnatal mouse inner ear progenitor/stem cells (mIESCs) are viable after transplantation into the basal turns of neomycin-injured guinea pig cochleas. We also examined the effects of mIESC transplantation on auditory functions. Eight adult female Cavia porcellus guinea pigs (250-350g) were deafened by intratympanic neomycin delivery. After 7 days, the animals were randomly divided in two groups. The study group (n=4) received transplantation of LacZ-positive mIESCs in culture medium into the scala tympani. The control group (n=4) received culture medium only. At 2 weeks after transplantation, functional analyses were performed by auditory brainstem response measurement, and the animals were sacrificed. The presence of mIESCs was evaluated by immunohistochemistry of sections of the cochlea from the study group. Non-parametric tests were used for statistical analysis of the data. Intratympanic neomycin delivery damaged hair cells and increased auditory thresholds prior to cell transplantation. There were no significant differences between auditory brainstem thresholds before and after transplantation in individual guinea pigs. Some mIESCs were observed in all scalae of the basal turns of the injured cochleas, and a proportion of these cells expressed the hair cell marker myosin VIIa. Some transplanted mIESCs engrafted in the cochlear basilar membrane. Our study demonstrates that transplanted cells survived and engrafted in the organ of Corti after cochleostomy.

A novel missense mutation p.L76P in the GJB2 gene causing nonsyndromic recessive deafness in a Brazilian family.

Mutations in the GJB2 gene, encoding connexin 26 (Cx26), are a major cause of nonsyndromic recessive hearing loss in many countries. We report here on a novel point mutation in GJB2, p.L76P (c.227C>T), in compound heterozygosity with a c.35delG mutation, in two Brazilian sibs, one presenting mild and the other profound nonsyndromic neurosensorial hearing impairment. Their father, who carried a wild-type allele and a p.L76P mutation, had normal hearing. The mutation leads to the substitution of leucine (L) by proline (P) at residue 76, an evolutionarily conserved position in Cx26 as well as in other connexins. This mutation is predicted to affect the first extracellular domain (EC1) or the second transmembrane domain (TM2). EC1 is important for connexon-connexon interaction and for the control of channel voltage gating. The segregation of the c.227C>T (p.L76P) mutation together with c.35delG in this family indicates a recessive mode of inheritance. The association between the p.L76P mutation and hearing impairment is further supported by its absence in a normal hearing control group of 100 individuals, 50 European-Brazilians and 50 African-Brazilians.

Association of polymorphisms at the ADIPOR1 regulatory region with type 2 diabetes and body mass index in a Brazilian population with European or African ancestry.

Association studies between ADIPOR1 genetic variants and predisposition to type 2 diabetes (DM2) have provided contradictory results. We determined if two single nucleotide polymorphisms (SNP c.-8503G>A and SNP c.10225C>G) in regulatory regions of ADIPOR1 in 567 Brazilian individuals of European (EA; N = 443) or African (AfA; N = 124) ancestry from rural (quilombo remnants; N = 439) and urban (N = 567) areas. We detected a significant effect of ethnicity on the distribution of the allelic frequencies of both SNPs in these populations (EA: -8503A = 0.27; AfA: -8503A = 0.16; P = 0.001 and EA: 10225G = 0.35; AfA: 10225G = 0.51; P < 0.001). Neither of the polymorphisms were associated with DM2 in the case-control study in EA (SNP c.-8503G>A: DM2 group -8503A = 0.26; control group -8503A = 0.30; P = 0.14/SNP 10225C>G: DM2 group 10225G = 0.37; control group 10225G = 0.32; P = 0.40) and AfA populations (SNP c.-8503G>A: DM2 group -8503A = 0.16; control group -8503A = 0.15; P = 0.34/SNP 10225C>G: DM2 group 10225G = 0.51; control group 10225G = 0.52; P = 0.50). Similarly, none of the polymorphisms were associated with metabolic/anthropometric risk factors for DM2 in any of the three populations, except for HDL cholesterol, which was significantly higher in AfA heterozygotes (GC = 53.75 +/- 17.26 mg/dL) than in homozygotes. We conclude that ADIPOR1 polymorphisms are unlikely to be major risk factors for DM2 or for metabolic/anthropometric measurements that represent risk factors for DM2 in populations of European and African ancestries.

Correspondence regarding Ballana et al., "Mitochondrial 12S rRNA gene mutations affect RNA secondary structure and lead to variable penetrance in hearing impairment".

Ballana et al. [E. Ballana, E. Morales, R. Rabionet, B. Montserrat, M. Ventayol, O. Bravo, P. Gasparini, X. Estivill, Mitochondrial 12S rRNA gene mutations affect RNA secondary structure and lead to variable penetrance in hearing impairment, Biochem. Biophys. Res. Commun. 341 (2006) 950-957] detected a T1291C mutation segregating in a Cuban pedigree with hearing impairment. They interpreted it as probably pathogenic, based on family history, RNA conformation prediction and its absence in a control group of 95 Spanish subjects. We screened a sample of 203 deaf subjects and 300 hearing controls (110 "European-Brazilians" and 190 "African-Brazilians") for the mitochondrial mutations A1555G and T1291C. Five deaf subjects had the T1291C substitution, three isolated cases and two familial cases. In the latter, deafness was paternally inherited or segregated with the A1555G mutation. This doesn't support the hypothesis of T1291C mutation being pathogenic. Two "African-Brazilian" controls also had the T1291C substitution. Six of the seven T1291C-carriers (five deaf and two controls) had mitochondrial DNA of African origin, belonging to macrohaplogroup L1/L2. Therefore, these data point to T1291C substitution as most probably an African non-pathogenic polymorphism.