Genetics Factors and Natural History

Racial distribution and prevalence

Otosclerosis has only been demonstrated in Homo sapiens and is predominantly a disease of Caucasoid man, being a very common cause of deafness throughout Europe, the Balkans, the Middle East and the subcontinent of India, together with the Caucasian people of North and South America, Australia, New Zealand, South Africa and elsewhere. It also occurs, though less frequently in the negrito people of Malaya, New Guinea and the Philippines and in the Japanese, a mixed race of mongol, ainu and negrito blood.

It is relatively rarely found in mongoloid and negroid man. Racial distribution of Otosclerosis may be related to inherited deficiency of alpha-I-antitrypsin (AA), a deficiency which is rarely found in mongoloid man.

Age of Onset

Whether conductive, sensori-neural or combined the deafness of Otosclerosis is essentially a disease of adults. The hearing loss is first noted in 91 percent of cases between the ages of 15 and 45 years, with the peak in the third decade. In 2 percent the onset is under 10 years, in 3 percent between 10 and 15 years and in 4 percent over 45 years. The age of onset is the same for males and females.

Sex Distribution

It is more frequently in females than in males and a sex ratio of about 2 to 1.

Pregnancy and Otosclerosis

Hearing loss is first noticed during one pregnancy. During pregnancy the raised oestrogens, which cause fragility of the lysosomal membranes with release of enzymes, might initiate or activate the otosclerotic foci. The deafness of Otosclerosis can also increase in patients with thyrotoxicosis.

Mode of inheritance

For simple genetic counseling it can be stated that if two otosclerotic parents have issue about half their children will develop the clinical condition; and if an otosclerotic marries a non-otosclerotic about a quarter of their offspring will become deaf.

The degree of manifestation varies from family to family and even this appears to be genetically determined. Some families are encountered with 100 per cent manifestation, while other families show degrees of manifestation of as little as 10 per cent.



Other genetic factors

There is no evidence of either association or genetic linkage between Otosclerosis and the common blood groups, the hair or iris colour or the common genetic markers.

Because Otosclerosis is a very common condition it is found at times in patients with either common hereditary disorders such as diabetes mellitus and colour blindness and sometimes with rarer alleles such as retinitis pigmentosa or albinism. These associations are quite coincidental.



Otosclerosis
  • What is Otosclerosis?
  • How do we hear?
  • What causes Otosclerosis?
  • Symptoms of Otosclerosis?
  • How is Otosclerosis diagnosed?
  • Genetics Factors & Natural History
  • How is Otosclerosis treated?