Genetic and eugenic aspects of early total deafness

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Abstract
Early total deafness occurs when hearing is lost before speech is fully formed at the age of about 7-8 years. About 55% of the cases of early total deafness have an hereditary basis. Most genetic factors important in the etiology of early total deafness lead to preceptive deafness; i.e., the Organ of Corti is affected. While only a small proportion lead to types of conduction deafness, such as "endogenously" produced bilateral atresia of the external auditory canal. Even otosclerosis usually occurs after puberty and therefore accounts for only a small number of the early cases. There is not full agreement on the genetic mechanisms responsible for heredity early total deafness since a similar clinical picture obviously may be caused by various gene mechanisms. Thus congenital hereditary-degenerative dominant inner ear deafness which accounts for a few cases of early total deafness, is dominant in some pedigrees but polygenic or dependent on a recessive triple allelic system in others. Sporadic recessive deafness, a common form, is thought to be due to a single autosomal recessive gene. The genetic mechanisms underlying certain syndromes which include early total deafness, are in much dispute. Even the deafness group classed as apparently "exogenous" (non-hereditary) may include forms which are based on a genetic predisposition to environmentally induced deafness. There is need for more careful study of early total deafness in different families. The situation is further complicated by a great variability in expressivity of the genes involved both with respect to the time of onset and intensity of hearing loss. There is also incomplete penetrance in the cases of deafness dependent on a dominant gene. In heredity counseling, owing to the importance of recessive genetic mechanisms in the etiology of early total deafness, advice should be given against consanguinous marriages. If one or both partners are known to be genetically deaf, they may be counseled to consider childless marriages.
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