Clinical Trial: Genetic Analysis of Human Hereditary Hearing Impairment


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Sponsored by:	National Institute on Deafness and Other Communication Disorders (NIDCD)
Information provided by:	Warren G Magnuson Clinical Center (CC)

The study will begin by finding large families who have members with hearing impairment. Once families are found, members with and without hearing impairment will be evaluated by an audiologist and a clinician (doctor). An audiologist, is a person trained in evaluating, habilitating, and rehabilitating people with disorders of hearing function. The clinician's responsibility is to examine the patients and check for other signs and symptoms related to hearing.

Once all members of the family are evaluated researchers can create a pedigree. A pedigree is like a family tree that charts members of a family with a genetic disorder, like hearing impairment. Pedigrees are used to determine the mode of inheritance of the gene responsible for a particular condition.

Finally, researcher intend on using all the information gathered as well as methods for genetic analysis to map out the location of the gene. Patients participating in this study will not directly benefit from its research, but scientific understanding achieved may help researchers better understand the auditory system and someday prevent deafness.

Condition
Partial Hearing Loss

The objective of this research project is to map and clone genes that are important for the normal development or maintenance of the auditory system. One strategy for identifying some of the genes important for auditory processes is to ascertain large families each with several hearing impaired individuals. Initial contact will be made by family physicians, audiologist, supervisors in schools for the hearing impaired, and directly by the principal investigators during surveys of schools for the deaf and visits with hearing impairment self-help groups. Members of a family will be evaluated by an audiologist and instances of hearing impairment will be documented and categorized. A clinician would then examine hearing impaired and unaffected members of the family for the presence of other clinical features so as to distinguish between nonsyndromic and syndromic forms of hearing impairment. Pedigrees of these families will be analyzed to determine the mode of inheritance of the hereditary hearing impairment segregating in each family. Families will be ascertained through audiologists and other clinicians, genetics clinics, schools for the hearing impaired and through linguists and medical anthropologists who study unique sign languages and the sociology of communities with a high proportion of hearing impaired individuals. The mutated gene will then be genetically mapped by a linkage or association based strategy using DNA typing of highly polymorphic genetic markers distributed across the human genome.

INCLUSION CRITERIA:
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).
We seek subjects who are members of large families with multiple individuals affected with a hearing disorder. Sporadic cases will occasionally 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.
If there is evidence of genetic homogeneity, small families can be pooled for linkage analysis, or a combination of large and small families can be pooled.
Subjects of any ethnic background, gender, age, sexual orientation, or health status will be included.
EXCLUSION CRITERIA:
Patients will be excluded when their hearing or vestibular dysfunction are known to be cuased by a nongenetic etiology such as trauma, infection, metabolic or immunologic disorders, or exposure to ototoxic agents such as noise or aminoglycoside antibiotics.