Involvement of T-cell receptor-beta alterations in the development of otosclerosis linked to OTSC2

Brazilian Society of Otology task force - Otosclerosis: evaluation and treatment

OBJECTIVES

To review and provide evidence-based recommendations for the diagnosis and treatment of otosclerosis.

METHODS

Task force members were educated on knowledge synthesis methods, including electronic database search, review and selection of relevant citations, and critical appraisal of selected studies. Articles written in English or Portuguese on otosclerosis were eligible for inclusion. The American College of Physicians' guideline grading system and the American Thyroid Association's guideline criteria were used for critical appraisal of evidence and recommendations for therapeutic interventions.

RESULTS

The topics were divided into 2 parts: 1) Diagnosis - audiologic and radiologic; 2) Treatment - hearing AIDS, pharmacological therapy, stapes surgery, and implantable devices - bone-anchored devices, active middle ear implants, and Cochlear Implants (CI).

CONCLUSIONS

The pathophysiology of otosclerosis has not yet been fully elucidated, but environmental factors and unidentified genes are likely to play a significant role in it. Women with otosclerosis are not at increased risk of worsening clinical condition due to the use of contraceptives or during pregnancy. Drug treatment has shown little benefit. If the patient does not want to undergo stapedotomy, the use of hearing aids is well indicated. Implantable systems should be indicated only in rare cases, and the CI should be indicated in cases of profound deafness.

A pathogenic deletion in Forkhead Box L1 (FOXL1) identifies the first otosclerosis (OTSC) gene

Otosclerosis is a bone disorder of the otic capsule and common form of late-onset hearing impairment. Considered a complex disease, little is known about its pathogenesis. Over the past 20 years, ten autosomal dominant loci (OTSC1-10) have been mapped but no genes identified. Herein, we map a new OTSC locus to a 9.96 Mb region within the FOX gene cluster on 16q24.1 and identify a 15 bp coding deletion in Forkhead Box L1 co-segregating with otosclerosis in a Caucasian family. Pre-operative phenotype ranges from moderate to severe hearing loss to profound sensorineural loss requiring a cochlear implant. Mutant FOXL1 is both transcribed and translated and correctly locates to the cell nucleus. However, the deletion of 5 residues in the C-terminus of mutant FOXL1 causes a complete loss of transcriptional activity due to loss of secondary (alpha helix) structure. FOXL1 (rs764026385) was identified in a second unrelated case on a shared background. We conclude that FOXL1 (rs764026385) is pathogenic and causes autosomal dominant otosclerosis and propose a key inhibitory role for wildtype Foxl1 in bone remodelling in the otic capsule. New insights into the molecular pathology of otosclerosis from this study provide molecular targets for non-invasive therapeutic interventions.

Genetics of otosclerosis: finally catching up with other complex traits?

Otosclerosis is a relatively common cause of hearing impairment, characterized by abnormal bone remodeling of the middle and inner ear. In about 50-60% of the patients, the disease is present in a familial form. In most of these families, otosclerosis seems to be caused by a small number of genetic factors (oligogenic) while only in a small number of families the disease seems to be truly monogenic. In the remaining patients a complex genetic form of otosclerosis is present. Several studies have aimed to identify the genetic factors underlying otosclerosis, which has led to the identification of eight published loci for monogenic otosclerosis, as well as several genes and one chromosomal region (11q13.1) with a clear association with otosclerosis. Implementation of next-generation sequencing (NGS) in otosclerosis research has led to the identification of pathogenic variants in MEPE, ACAN and SERPINF1, although the pathogenic role of the latter is under debate. In addition, a recent GWAS can be considered a breakthrough for otosclerosis as it identified several strong associations with otosclerosis and suggested new potential candidate genes. These recent findings are important for unraveling the genetic architecture of otosclerosis. More future studies will help to understand the complete pathogenesis of the disease.

Analysis of the Genetic Characteristics of a Chinese Family With Otosclerosis

BACKGROUND

Otosclerosis is a focal lesion of the inner ear. The role of genetic factors in the pathogenesis of otosclerosis has received increasing attention. We analyzed the clinical manifestations, inheritance pattern, and pathogenic genes in a family with otosclerosis.

METHODS

We collected clinical data and generated a family pedigree. High-throughput second-generation sequencing technology was used to identify candidate genes by performing whole-exome sequencing of 7 members of the family, and Sanger sequencing was performed to validate candidate gene mutations in the 7 family members.

RESULTS

Otosclerosis was characterized by autosomal dominant inheritance in this family. Whole-exome sequencing did not reveal mutation sites in known deafness-related genes. However, a c.2209A > G (p.T737A) mutation was detected in exon 6 of the SP1 gene, which is associated with the COL1A1 gene. This mutation was a pathogenic mutation, and Sanger sequencing confirmed that this mutation cosegregated with the clinical phenotype among the family members.

CONCLUSIONS

The pattern of otosclerosis in this family is consistent with autosomal dominant inheritance, and the SP1 gene, harboring the c.2209A > G (p.T737A) mutation in exon 6, may be the causative gene of otosclerosis in this family.

Genetic association analysis in a clinically and histologically confirmed otosclerosis population confirms association with the TGFB1 gene but suggests an association of the RELN gene with a clinically indistinguishable otosclerosis-like phenotype

BACKGROUND/HYPOTHESIS

Otosclerosis is a frequent cause of hearing impairment characterized by abnormal resorption and deposition of bone in the human otic capsule. It is a disease of complex etiopathogenesis that is caused by both environmental and genetic factors. The goal of this study is to replicate association for genes that were previously reported to be associated with otosclerosis. However, in this study, patients were used in which the presence of otosclerotic foci was confirmed by histologic investigation, in contrast to previous studies, that did not use histologic confirmation.

METHODS

Case-control association study using 153 cases and 300 controls. Thirteen single nucleotide polymorphisms (SNPs) in 6 genes (COL1A1, TGFB1, BMP2, BMP4, AGT, and RELN) were genotyped.

RESULTS

An association between TGFB1 (rs1800472) and otosclerosis was detected, confirming several previous reports. It is surprising that no association was found between RELN and otosclerosis because the current analysis had very reasonable power and the RELN association has been published before in different articles using several independent populations.

CONCLUSION

Our findings strengthen the association of TGFB1 (rs1800472) with otosclerosis. The fact that other genes did not replicate could be due to different reasons like lack of power (BMP2 and BMP4) and possible false-positive initial association (COL1A1 and AGT). A plausible explanation for the lack of association for RELN is that RELN could be associated with a specific otosclerosis-like phenotype that is different from the histologically confirmed phenotype of the patients in this study, and that is clinically not distinguishable.

Rare variants in BMP2 and BMP4 found in otosclerosis patients reduce Smad signaling

HYPOTHESIS

Genetic variation in BMP2 and BMP4 found in otosclerosis patients result in altered Smad signaling.

BACKGROUND

Otosclerosis is a common form of adult-onset conductive hearing loss resulting from abnormal bone remodeling of the bony labyrinth that surrounds the inner ear. Both genetic and environmental factors are implicated in the disease, yet very little is known about its pathogenesis. The evidence for a genetic component has been established through family-based linkage and population-based association studies. Previously, members of the TGF-β superfamily of genes have been associated with otosclerosis.

METHODS

Sequencing of BMP2 and BMP4 coding regions was performed to identify common and rare variation in German otosclerosis patients compared with controls. Functional analyses of rare variation in the patient cohort were conducted by exposing an osteosarcoma cell line to conditioned media containing either wild type or variant forms of BMP2 or BMP4 and analyzing Smad1/5/8 phosphorylation.

RESULTS

Although no significant association with common variation in these 2 genes was detected, there were 8 singleton variants identified in the German population. Of the 4 coding variants found solely in otosclerosis patients, two--BMP4(N150K) and BMP2(K357-R396del)--were found to decrease Smad1/5/8 signaling.

CONCLUSION

Rare variants in BMP2 and BMP4 are not a major genetic component in the otosclerosis population. However, those with functional affect showed decreased Smad signaling. Further analysis of Smad signaling molecules should be performed to determine if these pathways in combination are a major contributor to otosclerosis, which could lead to additional treatment options for otosclerosis patients.

An introduction of genetics in otosclerosis: a systematic review

OBJECTIVE

To present an easy to read systematic review concerning the genetic etiology of otosclerosis to help health care providers in counseling otosclerosis patients more accurately.

DATA SOURCES

PubMed, Embase, CINAHL, and the Cochrane Library.

REVIEW METHODS

Studies on the genetic etiology of otosclerosis were selected. Association studies and family-based studies were included for further review. After quality assessment (risk of bias), data were extracted from the included studies. When available, odds ratios were presented. In case of corresponding genetic anomalies between the studies, it was the aim to combine results.

RESULTS

The number of available studies with low risk of bias is limited to 2 association studies and 1 family-based study. These high-quality studies show that otosclerosis in Japanese patients is not linked to the NOG gene and that a polymorphism in the Sp1 binding site located on the COL1A1 gene is associated with otosclerosis as well as OTSC1. Association and family-based studies with moderate risk of bias show a statistically significant association with the ACE gene, AGT gene, OTSC2, RELN gene, TGFB1 gene, 11q13.1, OTSC2, OTSC5, OTSC8, and OTSC10. These results may be spurious associations due to their bias and low statistical power.

CONCLUSION

The present systematic review shows that there is scattered evidence of limited quality and a lack of replication studies. It is not possible to point out 1 or more responsible genes, which play a key role within the genetic pathophysiologic mechanism of otosclerosis.

Complex-disease networks of trait-associated single-nucleotide polymorphisms (SNPs) unveiled by information theory

Objective

Thousands of complex-disease single-nucleotide polymorphisms (SNPs) have been discovered in genome-wide association studies (GWAS). However, these intragenic SNPs have not been collectively mined to unveil the genetic architecture between complex clinical traits. The authors hypothesize that biological annotations of host genes of trait-associated SNPs may reveal the biomolecular modularity across complex-disease traits and offer insights for drug repositioning.

Methods

Trait-to-polymorphism (SNPs) associations confirmed in GWAS were used. A novel method to quantify trait–trait similarity anchored in Gene Ontology annotations of human proteins and information theory was developed. The results were then validated with the shortest paths of physical protein interactions between biologically similar traits.

Results

A network was constructed consisting of 280 significant intertrait similarities among 177 disease traits, which covered 1438 well-validated disease-associated SNPs. Thirty-nine percent of intertrait connections were confirmed by curators, and the following additional studies demonstrated the validity of a proportion of the remainder. On a phenotypic trait level, higher Gene Ontology similarity between proteins correlated with smaller ‘shortest distance’ in protein interaction networks of complexly inherited diseases (Spearman p<2.2×10⁻¹⁶). Further, ‘cancer traits’ were similar to one another, as were ‘metabolic syndrome traits’ (Fisher's exact test p=0.001 and 3.5×10⁻⁷, respectively).

Conclusion

An imputed disease network by information-anchored functional similarity from GWAS trait-associated SNPs is reported. It is also demonstrated that small shortest paths of protein interactions correlate with complex-disease function. Taken together, these findings provide the framework for investigating drug targets with unbiased functional biomolecular networks rather than worn-out single-gene and subjective canonical pathway approaches.