[Hereditary unilateral deaf-mutism as a variable manifestation of bilateral deaf-mutism or hearing loss]

A total of 2,519 patients with bilateral severe congenital deafness (deaf-mutism) from Central Switzerland were recorded during the period between 1834 to 1979. More recently, 31 persons with unilateral severe deafness were examined. By constructing genealogical charts going back to the 17th century, at least ten of these unilaterally deaf persons were shown to be related to patients with bilateral deafness (pedigrees I-IV). Some of them exhibited a more or less marked Klein- Waardenburg syndrome. The unilateral deafness of those patients was inherited and not acquired. Congenital unilateral deafness may be understood to be the result of the broad variability of the expressivity of acoustic defects.