Elevated autoantibodies in sera from otosclerotic patients are related to the disease duration

The etiology of otosclerosis: a combination of genes and environment

Otosclerosis is a common form of hearing loss characterized by abnormal bone remodeling in the otic capsule. It is a complex genetic disease, caused by a combination of genetic and environmental factors. During the past decade, several attempts have been made to identify factors for otosclerosis. This review provides an overview of the current understanding of the etiology of otosclerosis and describes the genetic and environmental factors that have been implicated in the disease. Environmental factors include fluoride and viral factors, particularly measles. Genetic association studies for otosclerosis have reported several associations of genetic variants that influence the risk of disease, mainly involving bone remodeling pathways, although their individual risk contributions are small. Rare monogenic forms of otosclerosis also exist, which are caused by a mutation in a single gene leading to a clear familial segregation of the disease. Linkage analysis of large otosclerosis families has led to the identification of seven loci, and recently evidence was found that T cell receptor beta is a gene responsible for familial otosclerosis, suggesting an underlying immunological pathway. However, this might also represent an autoimmune process, a hypothesis that is supported by other data as well. In conclusion, a variety of pathways have been identified to be involved in the development of otosclerosis, showing that distinct mechanisms involving both genetic and environmental risk factors can influence and contribute to a similar disease outcome.

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

Otosclerosis is a common form of hearing loss, characterized by disordered bone remodeling in the otic capsule. Within the otosclerotic foci, several immunocompetent cells and immune-modulating factors can be found. Different etiological theories involving the immune system have been suggested. However, a genetic component is clearly present. In large otosclerosis families, seven autosomal-dominant loci have been found, but none of the disease-causing genes has been identified. This study focused on the exploration of the second otosclerosis locus on chromosome 7q34-36 (OTSC2), holding the T-cell receptor beta locus (TRB locus). A significantly lower T-cell receptor-beta (TCR-beta) mRNA expression and percentage of blood circulating TCR-alphabeta(+) T cells was detected in OTSC2 patients compared with controls and patients with the complex form of the disease. Further analysis illustrated more significant disturbances in specific T-cell subsets, including an increased CD28(null) cell population, suggesting a disturbed T-cell development and ageing in OTSC2 patients. These disturbances could be associated with otosclerotic bone remodeling, given the known effects of immunocompetent cells on bone physiology. These data implicate the TRB locus as the causative gene in the OTSC2 region and represent an important finding in the elucidation of the disease pathology.

Genetics of otosclerosis

OBJECTIVES

Otosclerosis is a major cause of acquired hearing loss in adult life affecting exclusively the human temporal bone. Until recently, the etiopathogenesis of otosclerosis was still a matter of debate. Genetic research, however, has evolved enormously the last years and unveiled important clues regarding the cause of otosclerosis. The objective of this article is to review the genetics of otosclerosis with special attention for the links to the bone homeostasis of the otic capsule.

DATA SOURCES

A detailed literature study was performed focusing on the recent genetic findings in otosclerosis and the special bone turnover of the otic capsule. A PubMed search and own research data were used to bring the relevant information for this review together.

CONCLUSION

Unlike all other bones in the human skeleton, the otic capsule undergoes very little remodeling after development, possibly due to local inner ear factors. Otosclerosis is a process of pathologic increased bone turnover in the otic capsule, which in most cases leads to stapes fixation, resulting in a conductive hearing loss. Although environmental factors such as estrogens, fluoride, and viral infection have been implicated, it is clear that genetic factors play a significant role in the manifestation of otosclerosis. From a genetic viewpoint, otosclerosis is considered to be a complex disease with rare autosomal dominant forms caused by a single gene. Already, 7 monogenic loci have been published, but none of the genes involved have been identified. For the complex form of otosclerosis, caused by an interaction between genetic and environmental factors, the first susceptibility genes were identified by case-control association studies. All 3 replicated genes, TGFB1, BMP2, and BMP4, are a part of the transforming growth factor-beta1 pathway. Data from both genetic association studies and gene expression analysis of otosclerotic bone showed that the TGF-beta1 pathway is most likely an important factor in the pathogenesis of otosclerosis.

An overview of the etiology of otosclerosis

Otosclerosis is the primary disease affecting the homeostasis of otic capsule and is among the most common causes of acquired hearing loss. Otosclerosis is considered as a multifactor disease, caused by both genetic and environmental factors. The aim of the present review is to summarize and analyze the bibliographic data, associated with the etiology of the disease. In some cases, the otosclerosis has an autosomal dominant mode of inheritance with incomplete penetrance. Genetic studies reveal the occurrence of at least nine chromosomal loci as candidate genes of the disease. The localized measles virus infection of the otic capsule has been postulated as a possible etiological theory. The role of hormonal factors, immune and bone-remodeling system in the etiopathogenesis of otosclerosis and the association of the disease with the disorders of the connective tissue are the issues of the present study. Despite the extensive research, many etiological factors and theories have been suggested and the process of development of the otosclerosis remains unclear.

Current research in otosclerosis

PURPOSE OF REVIEW

The aim of this article is to summarize and put into historical perspective current advances in research in otosclerosis, a disorder of the human temporal bone with a hereditary predisposition that is among the most common causes of acquired hearing loss.

RECENT FINDINGS

Genetic studies have revealed that otosclerosis is heterogeneous, with evidence for defects in at least seven genes associated with six distinct chromosomal loci. Measurements of high levels of osteoprotegerin expression in the normal otic capsule and soft tissues of the cochlea provide the first molecular insight as to why the normal otic capsule remodels minimally, if at all. Osteoprotegerin knockout mice provide the best available animal model to date to study abnormal otic capsule remodeling that closely resembles otosclerosis. There is mounting evidence that the measles virus plays an important role in pathogenesis of otosclerosis although the mechanisms by which the virus results in otosclerosis remain unknown. Quantitative measures of angiogenesis can reliably distinguish between clinical and histological otosclerosis. Advances in the emerging field of osteoimmunology will likely impact and benefit from the research in otosclerosis.

SUMMARY

Insights into molecular mechanisms that inhibit extensive remodeling in the normal otic capsule, and understanding of how these mechanisms are dysregulated in otosclerosis will allow future design of rational treatment strategies for otosclerosis.

Audiovestibular disorders in patients with ankylosing spondylitis

OBJECTIVE

Audiovestibular disorders have been described in several autoimmune diseases but have not been studied in patients with ankylosing spondylitis (AS). The aim of this study was to evaluate the audiovestibular function in patients with AS.

METHODS

We prospectively evaluated 22 consecutive patients with AS. Clinical, radiologic, and immunogenetic features were analyzed. All patients underwent a complete ear, nose, and throat physical examination and audiologic evaluation that included pure-tone audiometry thresholds at octave frequencies of 250 to 8000 Hz, impedance audiometry (tympanogram, static compliance, acoustic reflexes, and reflex decay), and speech audiometry. Thirty-one healthy volunteers and 26 patients with rheumatoid arthritis (RA) were included as controls.

RESULTS

Patients with AS had a median age of 45.5 years (interquartile range [IQR] 38-54) and a median disease duration of 20 years (IQR 12.5-26.2). Otosclerosis was observed in 2 patients with AS (9.1%), 3 patients with RA (11.5%), but not in any healthy controls (P = not significant). Sensorineural hearing loss (SNHL) was observed in 13 patients with AS (59%), 17 patients with RA (65.4%), and 13 healthy controls (41.9%) without statistically significant differences. Because age can influence audiometric results, patients and controls were divided into 4 age groups. A higher frequency of SNHL was observed in patients with AS from 45 to 59 years compared with healthy controls and patients with RA (87% versus 20%, P = 0.03, versus 70%, P = not significant, respectively).

CONCLUSION

Middle-aged patients with AS had a significantly higher frequency of SNHL compared with controls. SNHL should be considered as a possible complication of AS as well as of RA and other autoimmune diseases. Possible toxic effect of nonsteroidal antiinflammatory drugs should also be considered in such patients.

The aetiology of otosclerosis: a review of the literature

During the last century, hundreds of studies have been performed to identify factors that are involved in the aetiology of otosclerosis. These studies include a variety of aetiological factors and, although many theories have been postulated, the process of the development of the disease remains unclear. A historical overview and analysis of the literature dealing with the aetiology of otosclerosis is presented. The role of collagen disorders, genetic linkage studies, associations with the HLA system and measles virus infection as causal factors is discussed. From an epidemiological point of view, the disease has an autosomal dominant mode of inheritance. Therefore, since the introduction of new genetic research techniques over the last decades, more studies have been performed to find evidence of a genetic factor that initiates the development of otosclerosis. In this review, we tried to categorize the most prominent studies in sections according to their subjects within the diversity of aetiological factors that have been studied.

[Possible benefits of calcitonin in the treatment of otosclerosis]

This study shows the results obtained after treatment with intranasal calcitonin in 23 patients (36 ears) suffering from otosclerosis. 19.4% showed a hearing improvement upper of 10 dB. The gain was 32 dB in air conduction thresholds and 23 dB. In bone conduction. Tinnitus disappeared in 25% of cases suffering from tinnitus. Calcitonin tolerance was good, 8.7% of patients reported migraine. Authors recommended additional studies in order to evaluate the efficacy of this drug in the treatment of otosclerosis.

Etiopathogenesis of otosclerosis

Otosclerosis is a frequent cause of nonsyndromic hearing loss which affects exclusively the human temporal bone. Various etiopathogenetic hypotheses have been proposed. The major hypotheses considered are genetic factors, immunologic factors and viral infection. Since the familial incidence of otosclerosis is known a recent genetic analysis has given evidence of three otosclerosis genes (OTSC1-3). Mutations in the collagen gene COL1A1 have been found in one large family with several cases of otosclerosis. Concerning an immunologic etiopathogenetic process, the presence of serum antibodies against collagen II and IX in patients with otosclerosis confirms the hypothesis of a collagen autoimmune mechanism. Finally as a possible cause of this chronic inflammatory disease morphologic and biochemical investigations have revealed a measles virus association. In conclusion, various etiopathogenetic factors may contribute to the genesis of otosclerosis.

Antimeasles immunoglobulin G in sera of patients with otosclerosis is lower than that in healthy people

BACKGROUND

There is some evidence for an inflammatory process as a driving force in otosclerosis. Two popular hypotheses for the induction of this chronic inflammation have been proposed: an autoimmune phenomenon induced by an otic capsule specific antigen and measles virus infection.

METHODS

Antibodies against measles virus hemagglutinin, polymerase, nucleocapsid, and matrix proteins were evaluated in sera from otosclerotic patients and in sera from healthy age-and sex-matched controls by use of the Western blot analyses.

RESULTS

Significant differences were not detected between healthy men and women or between otosclerotic men and women. There were significantly stronger reactions against all viral proteins in the group of healthy women as compared with otosclerotic women despite a high standard deviation. The group of healthy male blood donors demonstrated significantly stronger reactions against polymerase and nucleocapsid proteins. Healthy blood donors again demonstrated stronger reaction compared with respective otosclerotic patients in a separate reaction for viral matrix protein.

CONCLUSION

Our observation is consistent with viral participation in otosclerotic pathogenesis, but it is difficult to say if the diminished antimeasles humoral response is a consequence or the cause for a local measles infection. In light of the present data, we can discuss autoantibodies in otosclerosis as a sign of autoimmunity triggered by measles virus.

Pathophysiology of otosclerosis

OBJECTIVE

To review current knowledge of the pathophysiology of otosclerosis and to review hypotheses for the amelioration of this disease.

DATA SOURCES

Review of the literature and experimental observations by the authors.

CONCLUSIONS

Otosclerosis is a localized disease of bone remodeling within the otic capsule of the human temporal bone. Unlike other similar bone diseases, it does not occur outside of the temporal bone. These lesions seem to begin by resorption of stable otic capsule bone in adults, followed by a reparative phase with bone deposition. There are clearly genetic factors that lead to this disease, but measles virus infection and autoimmunity also may play contributing roles. Surgical correction of the conductive hearing loss is highly effective, but nonsurgical intervention has not yet been shown to prevent or slow the disease. Of the factors that may inhibit this process, fluorides, cytokine inhibitors, and bisphosphonates, third-generation bisphosphonates appear to hold the most promise.