Genetic diseases of hearing.

The study of genetic hearing loss has always been hindered by the difficulty of separating sporadic genetic cases from cases affected by environmental influences. This is because audiologic methods are largely insensitive to causes, and the anatomical location of the affected structures in the middle and inner ear makes histopathologic verifications difficult. With recent progress in genetic investigation, eg, the mapping of the gene location for the Waardenburg and Usher syndromes, both syndromic and nonsyndromic genotypes have been elucidated in humans and in animal models. In the future, molecular genetics will play an increasingly important role in the genetic counseling of suspected carriers, as well as in the prevention of additional hearing loss from exogenic causes (noise, ototoxic drugs) in confirmed cases of genetically vulnerable ears.