Clinical otosclerosis, the single most common cause of hearing impairment, is characterized by isolated endochondral bone sclerosis of the labyrinthine capsule. Otosclerotic foci invade the stapediovestibular joint (oval window) and interfere with free motion of the stapes. Mean age of onset is in the third decade and 90% of affected persons are under 50 years of age at the time of diagnosis. Approximately 10% of affected persons develop profound sensorineural hearing loss across all frequencies (summary by Tomek et al., 1998). Genetic Heterogeneity of Otosclerosis The locus associated with otosclerosis-1 (OTSC1) has been mapped to chromosome 15q26.1. Other loci associated with otosclerosis include OTSC2 (605727) on chromosome 7q; OTSC3 (608244) on chromosome 6p; OTSC4 (611571) on chromosome 16q; OTSC5 (608787) on chromosome 3q22-q24; OTSC7 (611572) on chromosome 6q13; OTSC8 (612096) on chromosome 9p13.1-q21.11; and OTSC10 (615589) on chromosome 1q41-q44. OTSC11 (620576) is caused by mutation in the FOXL1 gene (603252) on chromosome 16q24. OTSC12 (620792) is caused by mutation in the SMARCA4 gene (603254) on chromosome 19p13. The symbols OTSC6 and OTSC9 were reserved by the HUGO Gene Nomenclature Committee on January 30, 2003 and February 10, 2009, respectively, for as yet unpublished loci for otosclerosis.

A type of hearing loss resulting from a combination of conductive hearing impairment and sensorineural hearing impairment.