Otosclerosis: Role of infection and genetics

Otosclerosis is the commonest cause of non-suppurative conductive hearing loss in adults. It is a disease of the otic capsule characterized by vascular spongy bone formation causing fixation of the stapes and progressive conductive deafness. It is characterized by progressive hearing loss which is conductive in type, painless and often bilateral. An otosclerotic patient can hear better in noisy surrounding, the phenomenon being called paracusis willisii. Tinnitus and vertigo may also be associated with otosclerosis.

Schwartze sign in otosclerosis

The etiology of otosclerosis is not clear. Several factors like heredity, sex, race, metabolic disorders and endocrinal causes have been suggested.

Measles virus infection is considered to be associated with the development of otosclerosis. Presence of chronic inflammation have been shown in the otosclerotic foci and measles virus N, P and F protein have been shown to be present in the cells of the otosclerotic foci. Measles virus RNA has also been demonstrated in fresh frozen otosclerotic tissue. It has been hypothesized that the infection of the middle ear mucosa occurs via the Eustachian tube. The measles virus subsequently infects the bony labyrinth via the lymphatic or pericapillary space causing otosclerosis.

Genetic factors have also been found to be associated with otosclerosis. Majority of the present epidemiological studies found the disease to be associated with autosomal dominant inheritance. In one study, observing the inheritance of otosclerosis in a multigenerational family, an association was found with the FES-D15S657 region of the long arm of the 15^th chromosome. The gene mapped to this region is aggrecan the major non-collagenous component of the extracellular matrix of cartilage. In another genome wide analysis, variants in the RELN gene was associated with otosclerosis. The gene identified is in Chr 7q22.1.

These information suggest that apart from a viral etiology, genetic factors are important for the development of otosclerosis. The genetic factors and infection may be acting together to produce the final disease.

More information - 

• http://hmg.oxfordjournals.org/content/7/2/285.abstract
• http://content.karger.com/ProdukteDB/produkte.asp?Doi=98676
• http://www.cell.com/AJHG/abstract/S0002-9297(09)00046-9