Exclusion of TNFRSF11B as Candidate Gene for Otosclerosis in Campania Population

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.

Osteoprotegerin gene polymorphisms and otosclerosis: an additional genetic association study, multilocus interaction and meta-analysis

BACKGROUND

Otosclerosis (OTSC) is among the most common causes of a late-onset hearing loss in adults and is characterized by an abnormal bone growth in the otic capsule. Alteration in the osteoprotegerin (OPG) expression has been suggested in the implication of OTSC pathogenesis.

METHODS

A case-control association study of rs2228568, rs7844539, rs3102734 and rs2073618 single nucleotide polymorphisms (SNPs) in the OPG gene was performed in a Tunisian-North African population composed of 183 unrelated OTSC patients and 177 healthy subjects. In addition, a multilocus association and a meta-analysis of existing studies were conducted.

RESULTS

Rs3102734 (p = 0.013) and rs2073618 (p = 0.007) were significantly associated with OTSC, which were predominantly detected in females after multiple corrections. Among the OPG studied SNPs, the haplotypes A-A-C-G (p = 0.0001) and A-A-C-C (p = 0.0004) were significantly associated with OTSC in females. Multilocus association revealed that the SNPs: rs2073618 in OPG, rs1800472 in TGFβ1, rs39335, rs39350 and rs39374 in RELN, and rs494252 in chromosome 11 showed significant OTSC-associated alleles in Tunisian individuals. In addition, meta-analysis of the rs2073618 SNP in Tunisian, Indian and Italian populations revealed evidence of an association with OTSC (OR of 0.826, 95% CI [0.691-0.987], p = 0.035).

CONCLUSIONS

Our findings suggest that rs3102734 and rs2073618 variants are associated with OTSC in North African ethnic Tunisian population. Meta-analysis of the rs2073618 in three different ethnic population groups indicated an association with OTSC.

Genetic association and altered gene expression of osteoprotegerin in otosclerosis patients

Otosclerosis (OTSC) is a late-onset hearing disorder characterized by increased bone turnover in the otic capsule. Disturbed osteoprotegerin expression has been found in the otosclerotic foci which may have an important role in the pathogenesis of OTSC. To identify the genetic risk factors, we sequenced the coding region and exon-intron boundaries of the OPG gene in 254 OTSC patients and 262 controls. Sequence analysis identified five known polymorphisms c.9C>G, c.30+15C>T, c.400+4C>T, c.768A>G, and c.817+8A>C. Testing of these SNPs revealed sex specific association with c.9C>G in males and c.30+15C>T in females after multiple correction. Furthermore, meta-analysis provided evidence of association of the c.9C>G polymorphism with OTSC. In secondary analysis, we investigated the mRNA expression of OPG and associated genes RANK and RANKL in otosclerotic tissues compared to controls. Expression analysis revealed significantly missing/reduced OPG expression only in otosclerotic tissues. However, the signal sequence polymorphism c.9C>G has shown no effect on OPG mRNA expression. In conclusion, our results suggest that the risk of OTSC is influenced by variations in the OPG gene along with other factors which might regulate its altered expression in otosclerotic tissues. Further research is warranted to elucidate the mechanisms underlying these observations.