Waardenburg Syndrome: The Contribution of Next-Generation Sequencing to the Identification of Novel Causative Variants

Waardenburg syndrome (WS) is characterized by hearing loss and pigmentary abnormalities of the eyes, hair, and skin. The condition is genetically heterogeneous, and is classified into four clinical types differentiated by the presence of dystopia canthorum in type 1 and its absence in type 2. Additionally, limb musculoskeletal abnormalities and Hirschsprung disease differentiate types 3 and 4, respectively. Genes PAX3, MITF, SOX10, KITLG, EDNRB, and EDN3 are already known to be associated with WS. In WS, a certain degree of molecularly undetected patients remains, especially in type 2. This study aims to pinpoint causative variants using different NGS approaches in a cohort of 26 Brazilian probands with possible/probable diagnosis of WS1 (8) or WS2 (18). DNA from the patients was first analyzed by exome sequencing. Seven of these families were submitted to trio analysis. For inconclusive cases, we applied a targeted NGS panel targeting WS/neurocristopathies genes. Causative variants were detected in 20 of the 26 probands analyzed, these being five in PAX3, eight in MITF, two in SOX10, four in EDNRB, and one in ACTG1 (type 2 Baraitser-Winter syndrome, BWS2). In conclusion, in our cohort of patients, the detection rate of the causative variant was 77%, confirming the superior detection power of NGS in genetically heterogeneous diseases.

Generation of four induced pluripotent stem cells lines from PBMC of the DFNA58 family members: Two hearing-impaired duplication carriers (USPi006-A e USPi007-A) and two normal-hearing noncarriers (USPi004-A and USPi005-A)

The DFNA58 locus contains a genomic duplication involving three protein-coding genes (CNRIP1, PLEK, and PPP3R1's exon 1) and other uncharacterized lncRNA genes (LOC101927723, LOC107985892 and LOC102724389). To clarify the role of these genes in hearing and precisely determine their role in hearing loss, four iPSC lines were generated from two carriers and two noncarriers of the duplication.

Hearing aid effectiveness on patients with chronic tinnitus and associated hearing loss

OBJECTIVE

Our study aimed to measure the effectiveness of using HA in reducing the disturbance caused by tinnitus.

METHODS

Study was designed as a within-subjects clinical trial. Nineteen patients with chronic tinnitus and untreated sensorineural hearing loss were under counseling, HA fitting and 6 months follow-up. Tinnitus assessment was performed with Tinnitus Handicap Inventory (THI), Visual Analog Scale (VAS), pitch and loudness matching, and Minimum Masking Level measurements (MML).

RESULTS

following 6 months of HA use, a reduction in reported tinnitus and hearing handicap scales scores was observed both statistically and clinically. The pitch and loudness matching, as well as MML at the baseline and final evaluation were compared. MML's thresholds reduced significantly after 6 months of HA use.

CONCLUSION

Our study has provided evidence that HA fitting is a valuable treatment strategy for chronic tinnitus relief and associated hearing loss subtype of patient.

LEVEL OF EVIDENCE: 3

Genetic etiology of non-syndromic hearing loss in Latin America

Latin America comprises all countries from South and Central America, in addition to Mexico. It is characterized by a complex mosaic of regions with heterogeneous genetic profiles regarding the geographical origin of the ancestors and proportions of admixture between the Native American, European and African components. In the first years following the findings of the role of the GJB2/GJB6 genes in the etiology of hearing loss, most scientific investigations about the genetics of hearing loss in Latin America focused on assessing the frequencies of pathogenic variants in these genes. More recently, modern techniques allowed researchers in Latin America to make exciting contributions to the finding of new candidate genes, novel mechanisms of inheritance in previously known genes, and characterize a wide diversity of variants, many of them unique to Latin America. This review aimed to provide a general landscape of the genetic studies about non-syndromic hearing loss in Latin America and their main scientific contributions. It allows the conclusion that, although there are similar contributions of some genes, such as GJB2/GJB6, when compared to European and North American countries, Latin American populations revealed some peculiarities that indicate the need for tailored strategies of screening and diagnosis to specific geographic regions.

Molecular and genetic characterization of a large Brazilian cohort presenting hearing loss

Hearing loss is one of the most common sensory defects, affecting 5.5% of the worldwide population and significantly impacting health and social life. It is mainly attributed to genetic causes, but their relative contribution reflects the geographical region's socio-economic development. Extreme genetic heterogeneity with hundreds of deafness genes involved poses challenges for molecular diagnosis. Here we report the investigation of 542 hearing-impaired subjects from all Brazilian regions to search for genetic causes. Biallelic GJB2/GJB6 causative variants were identified in 12.9% (the lowest frequency was found in the Northern region, 7.7%), 0.4% carried GJB2 dominant variants, and 0.6% had the m.1555A > G variant (one aminoglycoside-related). In addition, other genetic screenings, employed in selected probands according to clinical presentation and presumptive inheritance patterns, identified causative variants in 2.4%. Ear malformations and auditory neuropathy were diagnosed in 10.8% and 3.5% of probands, respectively. In 3.8% of prelingual/perilingual cases, Waardenburg syndrome was clinically diagnosed, and in 71.4%, these diagnoses were confirmed with pathogenic variants revealed; seven out of them were novel, including one CNV. All these genetic screening strategies revealed causative variants in 16.2% of the cases. Based on causative variants in the molecular diagnosis and genealogy analyses, a probable genetic etiology was found in ~ 50% of the cases. The present study highlights the relevance of GJB2/GJB6 as a cause of hearing loss in all Brazilian regions and the importance of screening unselected samples for estimating frequencies. Moreover, when a comprehensive screening is not available, molecular diagnosis can be enhanced by selecting probands for specific screenings.

A rare genomic duplication in 2p14 underlies autosomal dominant hearing loss DFNA58

Here we define a ~200 Kb genomic duplication in 2p14 as the genetic signature that segregates with postlingual progressive sensorineural autosomal dominant hearing loss (HL) in 20 affected individuals from the DFNA58 family, first reported in 2009. The duplication includes two entire genes, PLEK and CNRIP1, and the first exon of PPP3R1 (protein coding), in addition to four uncharacterized long non-coding (lnc) RNA genes and part of a novel protein-coding gene. Quantitative analysis of mRNA expression in blood samples revealed selective overexpression of CNRIP1 and of two lncRNA genes (LOC107985892 and LOC102724389) in all affected members tested, but not in unaffected ones. Qualitative analysis of mRNA expression identified also fusion transcripts involving parts of PPP3R1, CNRIP1 and an intergenic region between PLEK and CNRIP1, in the blood of all carriers of the duplication, but were heterogeneous in nature. By in situ hybridization and immunofluorescence, we showed that Cnrip1, Plek and Ppp3r1 genes are all expressed in the adult mouse cochlea including the spiral ganglion neurons, suggesting changes in expression levels of these genes in the hearing organ could underlie the DFNA58 form of deafness. Our study highlights the value of studying rare genomic events leading to HL, such as copy number variations. Further studies will be required to determine which of these genes, either coding proteins or non-coding RNAs, is or are responsible for DFNA58 HL.

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.

New Insights on the Effect of TNF Alpha Blockade by Gene Silencing in Noise-Induced Hearing Loss

Noise exposure represents the second most common cause of acquired sensorineural hearing loss and we observed that tumor necrosis factor α (TNFα) was involved in this context. The effect of Tnfα gene silencing on the expression profile related to the TNFα metabolic pathway in an experimental model of noise-induced hearing loss had not previously been studied. Methods: Single ears of Wistar rats were pretreated with Tnfα small interfering RNA (siRNA) by trans-tympanic administration 24 h before they were exposed to white noise (120 dBSPL for three hours). After 24 h of noise exposure, we analyzed the electrophysiological threshold and the amplitude of waves I, II, III, and IV in the auditory brain response click. In addition, qRT-PCR was performed to evaluate the TNFα metabolic pathway in the ears submitted or not to gene silencing. Results: Preservation of the electrophysiological threshold and the amplitude of waves was observed in the ears submitted to gene silencing compared to the ears not treated. Increased anti-apoptotic gene expression and decreased pro-apoptotic gene expression were found in the treated ears. Conclusion: Our results allow us to suggest that the blockade of TNFα by gene silencing was useful to prevent noise-induced hearing loss.

Further evidence for loss-of-function mutations in the CEACAM16 gene causing nonsyndromic autosomal recessive hearing loss in humans

Mutations in the CEACAM6 gene were first described as causing autosomal dominant nonsyndromic hearing loss, but two splice-altering variants have been recently described as causing autosomal recessive nonsyndromic hearing loss. We describe the novel and extremely rare loss-of-function variant c.436 C > T/p.(Arg146Ter) in the CEACAM16 gene segregating with post-lingual progressive autosomal recessive hearing loss. This variant is predicted to significantly reduce the size of the wild type protein. Our results give additional support that loss-of-function variants in CEACAM16 cause autosomal recessive hearing loss in humans.

Syndromic hearing loss molecular diagnosis: Application of massive parallel sequencing

Syndromic hearing loss accounts for approximately 30% of all cases of hearing loss due to genetic causes. Mutation screening in known genes is important because it potentially sheds light on the genetic etiology of hearing loss and helps in genetic counseling of families. In this study, we describe a customized Ion AmpliSeq Panel, specifically designed for the investigation of syndromic hearing loss. The Ion AmpliSeq Panel was customized to cover the coding sequences of 52 genes. Twenty-four patients were recruited: 17 patients with a clinical diagnosis of a known syndrome, and seven whose clinical signs did not allow identification of a syndrome. Of 24 patients sequenced, potentially causative mutations were found in nine, all of which belonged to the group with a previous clinical diagnostic and none in the group not clinically diagnosed. We were able to provide conclusive molecular diagnosis to six patients, constituting a diagnostic rate of 25% (6/24). In the group of patients with a suspected clinical diagnosis, the diagnostic rate was 35% (6/17). Of the nine different mutations identified, three are novel, and were found in patients with Waardenburg, Treacher Collins and CHARGE syndromes. Since all patients with a conclusive molecular diagnosis through this panel had a previous suspected clinical diagnosis, our results suggest that this panel was more effective in diagnosing this group of patients. Therefore, the panel demonstrated effectiveness in molecular diagnosis when compared to others in the literature, especially for patients with a defined clinical diagnosis.

Mutation analysis of SLC26A4 (Pendrin) gene in a Brazilian sample of hearing-impaired subjects

Background

Mutations in the SLC26A4 gene are associated with Pendred syndrome and autosomal recessive non-syndromic deafness (DFNB4). Both disorders have similar audiologic characteristics: bilateral hearing loss, often severe or profound, which may be associated with abnormalities of the inner ear, such as dilatation of the vestibular aqueduct or Mondini dysplasia. But, in Pendred syndrome (OMIM #274600), with autosomal recessive inheritance, besides congenital sensorineural deafness, goiter or thyroid dysfunctions are frequently present. The aim of this study was to determine whether mutations in SLC26A4 are a frequent cause of hereditary deafness in Brazilian patients.

Methods

Microsatellite haplotypes linked to SLC26A4 were investigated in 68 families presenting autosomal recessive non-syndromic deafness. In the probands of the 16 families presenting segregation consistent with linkage to SLC26A4, Sanger sequencing of the 20 coding exons was performed. In an additional sample of 15 individuals with suspected Pendred syndrome, because of the presence of hypothyroidism or cochleovestibular malformations, the SLC26A4 gene coding region was also sequenced.

Results

In two of the 16 families with indication of linkage to SLC26A4, the probands were found to be compound heterozygotes for probably pathogenic different mutations: three novel (c.1003 T > G (p. F335 V), c.1553G > A (p.W518X), c.2235 + 2 T > C (IVS19 + 2 T > C), and one already described, c.84C > A (p.S28R). Two of the 15 individuals with suspected Pendred syndrome because of hypothyreoidism or cochleovestibular malformations were monoallelic for likely pathogenic mutations: a splice mutation (IVS7 + 2 T > C) and the previously described c.1246A > C (p.T416P). Pathogenic copy number variations were excluded in the monoallelic cases and in those with normal results after Sanger sequencing. Additional mutations in the SLC26A4 gene or other definite molecular cause for deafness were not identified in the monoallelic patients, after exome sequencing.

Conclusions

Biallelic pathogenic mutations in SLC26A4 explained ~ 3% of cases selected because of autosomal recessive deafness. Monoallelic mutations were present in ~ 13% of isolated cases of deafness with cochleovestibular malformations or suspected Pendred syndrome. These data reinforce the importance of mutation screening of SLC26A4 in Brazilian subjects and highlight the elevated frequency of monoallelic patients.

Polyethylene glycol fusion associated with antioxidants: A new promise in the treatment of traumatic facial paralysis

BACKGROUND

Recent studies in invertebrates have taught us that early cell membrane regeneration is determinant for axonal recovery and survival after trauma. Many authors obtained extraordinary results in neural regeneration using polyethylene glycol fusion protocols, which also involved microsutures and antioxidants.

METHODS

Sixty rats were evaluated with functional and histological protocol after facial nerve neurotmesis. Groups A and B had their stumps coapted with microsuture after 24 hours of neurotmesis and groups C and D after 72 hours. In addition to the microstructure, groups B and D used the polyethylene glycol-fusion protocol for the modulation of the Ca⁺² .

RESULTS

At the sixth week, the latency of group D and duration of group B was lower than groups A and C (P = .011). The axonal diameter of the groups that used polyethylene glycol-fusion was higher than those who did not use polyethylene glycol-fusion (P ≤ .001).

CONCLUSION

Although not providing a functional improvement, polyethylene glycol-fusion slowed down demyelination.

Evidence of progenitor cells in the adult human cochlea: sphere formation and identification of ABCG2

OBJECTIVES

The aim of this study was to search for evidence of stem or progenitor cells in the adult human cochlea by testing for sphere formation capacity and the presence of the stem cell marker ABCG2.

METHODS

Cochleas removed from patients undergoing vestibular schwannoma resection (n=2) and from brain-dead organ donors (n=4) were dissociated for either flow cytometry analysis for the stem cell marker ABCG2 or a sphere formation assay that is widely used to test the sphere-forming capacity of cells from mouse inner ear tissue.

RESULTS

Spheres were identified after 2-5 days in vitro, and the stem cell marker ABCG2 was detected using flow cytometric analysis after cochlear dissociation.

CONCLUSIONS

Evidence suggests that there may be progenitor cells in the adult human cochlea, although further studies are required.

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.

c.G2114A MYH9 mutation (DFNA17) causes non-syndromic autosomal dominant hearing loss in a Brazilian family

We studied a family presenting 10 individuals affected by autosomal dominant deafness in all frequencies and three individuals affected by high frequency hearing loss. Genomic scanning using the 50k Affymetrix microarray technology yielded a Lod Score of 2.1 in chromosome 14 and a Lod Score of 1.9 in chromosome 22. Mapping refinement using microsatellites placed the chromosome 14 candidate region between markers D14S288 and D14S276 (8.85 cM) and the chromosome 22 near marker D22S283. Exome sequencing identified two candidate variants to explain hearing loss in chromosome 14 [PTGDR – c.G894A:p.R298R and PTGER2 – c.T247G:p.C83G], and one in chromosome 22 [MYH9, c.G2114A:p.R705H]. Pedigree segregation analysis allowed exclusion of the PTGDR and PTGER2 variants as the cause of deafness. However, the MYH9 variant segregated with the phenotype in all affected members, except the three individuals with different phenotype. This gene has been previously described as mutated in autosomal dominant hereditary hearing loss and corresponds to DFNA17. The mutation identified in our study is the same described in the prior report. Thus, although linkage studies suggested a candidate gene in chromosome 14, we concluded that the mutation in chromosome 22 better explains the hearing loss phenotype in the Brazilian family.

7q36 deletion and 9p22 duplication: effects of a double imbalance

The etiology of mental retardation/developmental delay (MRDD) remains a challenge to geneticists and clinicians and can be correlated to environmental and genetic factors. Chromosomal aberrations are common causes of moderate to severe mental retardation and may represent 10% of these occurrences. Here we report the case of a boy with development delay, hypoplasia of corpus callosum, microcephaly, muscular hypotonia, and facial dysmorphisms. A deletion of 7q36.1 → 36.3 and duplication of 9p22.3 → 23 was detected as a result of an unbalanced translocation of paternal origin. Breakpoint delimitation was achieved with array comparative genomic hybridization assay. Additional multiplex ligation dependent probe amplification (MLPA) analyzes confirmed one copy loss of 7q36.3 region and one copy gain of 9p24.3 region. Patient resultant phenotype is consistent with the already described findings for both 7q deletion and 9p duplication syndromes.

Aberrant transcript produced by a splice donor site deletion in the TECTA gene is associated with autosomal dominant deafness in a Brazilian family

We ascertained a Brazilian family with nine individuals affected by autosomal dominant nonsyndromic sensorineural hearing loss. The bilateral hearing loss affected mainly mid-high frequencies, was apparently stable with an early onset. Microsatellites close to the DFNA8/DFNA12 locus, which harbors the TECTA gene, showed significant multipoint lod scores (3.2) close to marker D11S4107. Sequencing of the exons and exon-intron boundaries of the TECTA gene in one affected subject revealed the deletion c.5383+5delGTGA in the 5' end of intron 16, that includes the last two bases of the donor splice site consensus sequence. This mutation segregates with deafness within the family. To date, 33 different TECTA mutations associated with autossomal dominant hearing loss have been described. Among them is the mutation reported herein, first described by Hildebrand et al. (2011) in a UK family. The audioprofiles from the UK and Brazilian families were similar. In order to investigate the transcripts produced by the mutated allele, we performed cDNA analysis of a lymphoblastoid cell line from an affected heterozygote with the c.5383+5delGTGA and a noncarrier from the same family. The analysis allowed us to identify an aberrant transcript with skipping of exon 16, without affecting the reading frame. One of the dominant TECTA mutations already described, a synonymous substitution in exon 16 (c.5331G<A), was also shown to affect splicing, resulting in an aberrant transcript lacking exon 16. Despite the difference in the DNA level, both the synonymous substitution in exon 16 (c.5331G<A) and the mutation described herein affect splicing of exon 16, leading to its skipping. At the protein level they would have the same effect, an in-frame deletion of 37 amino-acids (p.S1758Y/G1759_N1795del) probably leading to an impaired function of the ZP domain. Thus, like the TECTA missense mutations associated with dominant hearing loss, the c.5383+5delGTGA mutation does not have an inactivating effect on the protein.

Duplications of BHLHA9 are associated with ectrodactyly and tibia hemimelia inherited in non-Mendelian fashion

BACKGROUND

Split-hand/foot malformation (SHFM)-also known as ectrodactyly-is a congenital disorder characterised by severe malformations of the distal limbs affecting the central rays of hands and/or feet. A distinct entity termed SHFLD presents with SHFM and long bone deficiency. Mouse models suggest that a defect of the central apical ectodermal ridge leads to the phenotype. Although six different loci/mutations (SHFM1-6) have been associated with SHFM, the underlying cause in a large number of cases is still unresolved.

METHODS

High resolution array comparative genomic hybridisation (CGH) was performed in patients with SHFLD to detect copy number changes. Candidate genes were further evaluated for expression and function during limb development by whole mount in situ hybridisation and morpholino knock-down experiments.

RESULTS

Array CGH showed microduplications on chromosome 17p13.3, a locus previously associated with SHFLD. Detailed analysis of 17 families revealed that this copy number variation serves as a susceptibility factor for a highly variable phenotype with reduced penetrance, particularly in females. Compared to other known causes for SHFLD 17p duplications appear to be the most frequent cause of SHFLD. A ~11.8 kb minimal critical region was identified encompassing a single gene, BHLHA9, a putative basic loop helix transcription factor. Whole mount in situ hybridisation showed expression restricted to the limb bud mesenchyme underlying the apical ectodermal ridge in mouse and zebrafish embryos. Knock down of bhlha9 in zebrafish resulted in shortening of the pectoral fins.

CONCLUSIONS

Genomic duplications encompassing BHLHA9 are associated with SHFLD and non-Mendelian inheritance characterised by a high degree of non-penetrance with sex bias. Knock-down of bhlha9 in zebrafish causes severe reduction defects of the pectoral fin, indicating a role for this gene in limb development.

Viable, Proliferating Progenitor Cells

Objective: Compare conditions and outcomes of otosphere suspension cultures from dissociated organ of Corti of either mouse or guinea pig at postnatal day 3 (P3), and to evaluate the guinea pig as a potential cochlea donor for preclinical cell therapy.

Method: Organs of Corti were isolated from P3 guinea pig or mouse cochlea, dissociated, and cultivated under nonadherent conditions as cell clusters (otospheres), in DMEM:F12 medium, supplemented with epidermal growth factor (EGF), plus either basic fibroblast growth factor (bFGF) or transforming growth factor alpha (TGFα), and submitted to immunofluorescence assays.

Results: Otospheres from mouse and guinea pig organ of Corti cultivated in vitro retained properties of inner ear progenitor cells, such as self-renewal, proliferation, and differentiation into hair cells or supporting cells. The best culture outcome was observed when mouse-derived cells were cultivated in the presence of TGFα instead of bFGF. Otosphere cell sorting will be additionally tested by flow cytometry of dissociated mouse cells. These ongoing experiments will be useful for the phenotype characterization of the progenitor cells presenting the best proliferating index.

Conclusion: The expression of sox2 and nestin in guinea pig and mouse otosphere is supporting evidence for the presence of inner ear progenitor cells in P3 guinea pig. However, the proliferation and differentiation potential of mouse-derived cells place this organism as a better model for studying early postnatal progenitor cell dynamics.

Candidate gene linkage analysis indicates genetic heterogeneity in Marfan syndrome

Marfan syndrome (MFS) is an autosomal dominant disease of the connective tissue that affects the ocular, skeletal and cardiovascular systems, with a wide clinical variability. Although mutations in the FBN1 gene have been recognized as the cause of the disease, more recently other loci have been associated with MFS, indicating the genetic heterogeneity of this disease. We addressed the issue of genetic heterogeneity in MFS by performing linkage analysis of the FBN1 and TGFBR2 genes in 34 families (345 subjects) who met the clinical diagnostic criteria for the disease according to Ghent. Using a total of six microsatellite markers, we found that linkage with the FBN1 gene was observed or not excluded in 70.6% (24/34) of the families, and in 1 family the MFS phenotype segregated with the TGFBR2 gene. Moreover, in 4 families linkage with the FBN1 and TGFBR2 genes was excluded, and no mutations were identified in the coding region of TGFBR1, indicating the existence of other genes involved in MFS. Our results suggest that the genetic heterogeneity of MFS may be greater that previously reported.

Retention of progenitor cell phenotype in otospheres from guinea pig and mouse cochlea

BACKGROUND

Culturing otospheres from dissociated organ of Corti is an appropriate starting point aiming at the development of cell therapy for hair cell loss. Although guinea pigs have been widely used as an excellent experimental model for studying the biology of the inner ear, the mouse cochlea has been more suitable for yielding otospheres in vitro. The aim of this study was to compare conditions and outcomes of otosphere suspension cultures from dissociated organ of Corti of either mouse or guinea pig at postnatal day three (P3), and to evaluate the guinea pig as a potential cochlea donor for preclinical cell therapy.

METHODS

Organs of Corti were surgically isolated from P3 guinea pig or mouse cochlea, dissociated and cultivated under non-adherent conditions. Cultures were maintained in serum-free DMEM:F12 medium, supplemented with epidermal growth factor (EGF) plus either basic fibroblast growth factor (bFGF) or transforming growth factor alpha (TGFα). Immunofluorescence assays were conducted for phenotype characterization.

RESULTS

The TGFα group presented a number of spheres significantly higher than the bFGF group. Although mouse cultures yielded more cells per sphere than guinea pig cultures, sox2 and nestin distributed similarly in otosphere cells from both organisms. We present evidence that otospheres retain properties of inner ear progenitor cells such as self-renewal, proliferation, and differentiation into hair cells or supporting cells.

CONCLUSIONS

Dissociated guinea pig cochlea produced otospheres in vitro, expressing sox2 and nestin similarly to mouse otospheres. Our data is supporting evidence for the presence of inner ear progenitor cells in the postnatal guinea pig. However, there is limited viability for these cells in neonatal guinea pig cochlea when compared to the differentiation potential observed for the mouse organ of Corti at the same developmental stage.

Spastic paraplegia, optic atrophy, and neuropathy: new observations, locus refinement, and exclusion of candidate genes

SPOAN is an autosomal recessive neurodegenerative disorder which was recently characterized by our group in a large inbred Brazilian family with 25 affected individuals. This condition is clinically defined by: 1. congenital optic atrophy; 2. progressive spastic paraplegia with onset in infancy; and 3. progressive motor and sensory axonal neuropathy. Overall, we are now aware of 68 SPOAN patients (45 females and 23 males, with age ranging from 5 to 72 years), 44 of which are presented here for the first time. They were all born in the same geographic micro region. Those 68 patients belong to 43 sibships, 40 of which exhibit parental consanguinity. Sixty-one patients were fully clinically evaluated and 64 were included in the genetic investigation. All molecularly studied patients are homozygotes for D11S1889 at 11q13. This enabled us to reduce the critical region for the SPOAN gene from 4.8 to 2.3 Mb, with a maximum two point lod score of 33.2 (with marker D11S987) and of 27.0 (with marker D11S1889). Three genes located in this newly defined critical region were sequenced, but no pathogenic mutation was detected. The gene responsible for SPOAN remains elusive.

A previously undescribed syndrome combining fibular agenesis/hypoplasia, oligodactylous clubfeet, anonychia/ungual hypoplasia, and other defects

We describe an apparently new genetic syndrome in six members of a family living in a remote area in Northeastern Brazil. This syndrome comprises: short stature due to a marked decrease in the length of the lower limbs (predominantly mesomelic with fibular agenesis/marked hypoplasia), grossly malformed/deformed clubfeet with severe oligodactyly, upper limbs with acromial dimples and variable motion limitation of the forearms and/or hands, severe nail hypoplasia/anonychia sometimes associated with mild brachydactyly and occasionally with pre-axial polydactyly. This syndrome is apparently distinct from the syndrome of brachydactyly-ectrodactyly with fibular aplasia or hypoplasia (OMIM 113310), the syndrome of fibular aplasia or hypoplasia, femoral bowing and poly-, syn-, and oligodactyly (OMIM 228930), and from other previously described conditions exhibiting fibular agenesis/hypoplasia.

Study of a Brazilian Family Presenting Non-syndromic hearing loss with mitochondrial inheritance

We hereby report on the audiological and genetic findings in individuals from a Brazilian family, with the following mitochondrial mutation A1555G in the 12SrRNA gene (MT-RNR-1). Nine individuals underwent speech, audiologic (tonal audiometry and logoaudiometry) and genetic evaluations. Eight individuals among the A1555G carriers were affected by hearing impairment and one person had normal hearing thresholds till the end of the present study. The audiologic evaluation results indicated normal hearing thresholds all the way to bilateral profound hearing loss with post-lingual onset and variable configuration. Two affected siblings presented progressive hearing loss. It was impossible to precise the time of hearing loss onset; however, the impairment was present in both children and adults. The genetic study revealed the A1555G mitochondrial mutation

Unexpected genetic heterogeneity in a large consanguineous Brazilian pedigree presenting deafness

Nonsyndromic autosomal recessive deafness accounts for 80% of hereditary deafness. To date, 52 loci responsible for autosomal recessive deafness have been mapped and 24 genes identified. Here, we report a large inbred Brazilian pedigree with 26 subjects affected by prelingual deafness. Given the extensive consanguinity found in this pedigree, the most probable pattern of inheritance is autosomal recessive. However, our linkage and mutational analysis revealed, instead of an expected homozygous mutation in a single gene, two different mutant alleles and a possible third undetected mutant allele in the MYO15A gene (DFNB3 locus), as well as evidence for other causes for deafness in the same pedigree. Among the 26 affected subjects, 15 were homozygous for the novel c.10573delA mutation in the MYO15A gene, 5 were compound heterozygous for the mutation c.10573delA and the novel deletion c.9957_9960delTGAC and one inherited only a single c.10573delA mutant allele, while the other one could not be identified. Given the extensive consanguinity of the pedigree, there might be at least one more deafness locus segregating to explain the condition in some of the subjects whose deafness is not clearly associated with MYO15A mutations, although overlooked environmental causes could not be ruled out. Our findings illustrate a high level of etiological heterogeneity for deafness in the family and highlight some of the pitfalls of genetic analysis of large genes in extended pedigrees, when homozygosity for a single mutant allele is expected.

Is autosomal recessive deafness associated with oculocutaneous albinism a "coincidence syndrome"?

Hearing impairment is frequently found associated with pigmentary disorders in many syndromes. However, total oculocutaneous albinism (OCA) associated with deafness has been described only once, by Ziprkowski and Adam (Arch Dermatol 89:151-155, 1964) in an inbred family. A syndrome associating deafness and OCA was suggested by the authors, but two separate recessive genes segregating in this inbred group were also proposed later by Fraser (OMIM # 220900). Combined deafness and total OCA were also observed by us in a family originally reported to be nonconsanguineous but in which haplotyping showed evidence of a common ancestry: the proband was affected by both diseases, one of his sisters had only OCA and another sister had only deafness. Both the proband and his deaf sister were found to be homozygotes for the 35delG mutation (GJB2 gene), the most frequent cause of hereditary deafness. Linkage analysis with markers close to the four known OCA loci excluded linkage to OCA1, OCA2, and OCA3, and homozygosity in markers near OCA4 locus was observed. Sequencing of the corresponding gene (MATP) revealed a c.1121delT mutation, which leads to a stop codon at position 397 (L374fsX397). Clearly, the combined occurrence of deafness and albinism in this pedigree was due to mutations in two different genes, showing autosomal recessive inheritance. We speculate that the putative syndrome reported by Ziprkowski and Adam might have resulted from the co-occurrence of autosomal recessive deafness and albinism in the same pedigree, as suggested by Fraser.

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.

Prevalence of the A1555G (12S rRNA) and tRNA Ser(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.

Spastic paraplegia, optic atrophy, and neuropathy is linked to chromosome 11q13

We report an autosomal recessive neurodegenerative disorder in 25 white members from a large inbred Brazilian family, 22 of whom were evaluated clinically. This condition is characterized by (1) subnormal vision secondary to apparently nonprogressive congenital optic atrophy; (2) onset of progressive spastic paraplegia in infancy; (3) onset of progressive motor and sensory axonal neuropathy in late childhood/early adolescence; (4) dysarthria starting in the third decade of life; (5) exacerbated acoustic startle response; and (6) progressive joint contractures and spine deformities. Motor handicap was severe, and all patients were wheelchair bound after 15 years old. We performed a genome-wide screen including 25 affected individuals and 49 of their unaffected relatives. Linkage was detected at 11q13 region with a maximum logarithm of odds score of +14.43, obtained with marker D11S1883. The candidate region, which lies between D11S1908 and D11S1889, encompasses approximately 4.8Mb and has more than 100 genes and expressed sequences. We propose the acronym SPOAN (spastic paraplegia, optic atrophy, and neuropathy) for this complex syndrome.