Hereditary hearing impairment is a genetically heterogeneous disorder that can be caused by mutations in any one of hundreds of different genes. Approximately 20 genes have now been identified in which mutations can cause nonsyndromic sensorineural hearing loss. The identification and analysis of these genes and their mutations are providing critical insights into the development, structure, and function of the auditory system, as well as the molecular mechanisms associated with disruption of these processes. In contrast, the molecular mechanisms underlying familial disorders affecting peripheral vestibular function appear to be more rare, have not been well described, and are less well understood. The peripheral auditory and vestibular systems share many common features in both health and disease, and many hereditary hearing loss disorders also affect vestibular function. The purpose of this study is to identify genes and mutations causing hereditary disorders of hearing, balance, or both. Members of families segregating hereditary disorders of hearing or balance will be enrolled in the proposed study in order to: (1) define and characterize the phenotypes and natural histories; (2) identify the underlying causative mutations and genes by linkage, positional cloning, and/or candidate gene mutation analyses; (3) and correlate observed phenotypes with the corresponding mutations and functions of the underlying genes.

• INCLUSION CRITERIA

Patients with known SNHL and/or peripheral vestibular dysfunction will be recruited.

It is anticipated that, in most cases, patients will be recruited whose disorders do not appear to be syndromic (i.e., are not associated with extra-auditory or extra-vestibular features).

Patients segregating abnormal auditory or vestibular phenotypes associated with novel syndromic phenotypes, or syndromes in which the causative gene has not been identified, will be eligible for this study.

The majority of subjects will be members of large families with multiple individuals affected with a hearing or balance disorder.

Sporadic cases will occassionally be included when the phenotype has features suggestive of mutations in one or a few particular candidate genes, since autosomal or X-Linked recessive inheritance can appear to be sporadic.

Children will be included when they are affected with the mutant phenotype or, based upon pedigree analysis, they may not be unaffected but are genetically informative and contributory for linkage mapping and identification of the mutated gene segregating in their family.

EXCLUSION CRITERIA

Patients will be excluded when their hearing or vestibular dysfunction is known to be caused by a nongenetic etiology such as trauma, infection, metabolic or immunologic disorders, or exposure to ototoxic agents such as noise or aminoglycoside antibiotics.