Biology Reference
In-Depth Information
Introduction and Overview:
Genetics in Auditory Science and
Clinical Audiology
BRONYA J. B. K EATS and CHARLES I. BERLIN
1. Introduction
The prevalence of genetic hearing loss varies among studies, but overall at
least 50% of hearing loss is genetic (Morton 1991; Marazita et al. 1993;
Nance and Pandya, Chapter 5). Furthermore, hearing loss that follows an
environmental insult (such as infection, acoustic trauma, exposure to oto-
toxic drugs) is likely to be influenced by genetic factors. Hearing loss is, in
fact, one of the most common genetic disorders, and a genetic etiology must
be considered for all patients with hearing loss. Identifying the underlying
causes of genetic hearing loss provides the clinical audiologist with useful
tools for diagnosis, prognosis, and, potentially, treatment for hearing
impaired patients. It also demonstrates that these genes, and the proteins
they encode, are critical for normal development of the auditory system.
Thus, all investigators interested in the auditory sciences, as well as patients
in audiological clinics, benefit from genetic studies of hearing loss.
Approximately one child in a thousand is born with profound hearing
impairment, and at least 70% have no associated anomalies (Gorlin et al.
1995). Analysis of data collected by Gallaudet University in the 1969-1970
Annual Survey of Hearing Impaired Children and Youth estimated that
genetic causes explained the hearing impairment in 50.7% of the children
(Nance et al. 1977), while analysis of the survey data collected two decades
later (1988-1989) estimated a genetic etiology in 62.8% of cases (Marazita
et al. 1993). A major reason for the increase in the proportion of profound
hearing impairment due to genetic factors was the reduction in cases due
to environmental causes (in particular, rubella).
Adult-onset hearing loss is also a significant health problem, with 14%
of individuals between the ages of 45 and 64, and 30% of those older than
65 years, having hearing problems (Hotchkiss 1989). Sill et al. (1994) col-
lected extensive population data in an attempt to delineate the causes of
later-onset hearing loss. The data strongly suggested a genetic etiology in a
large percentage of the participants, but a precise estimate could not be
determined.
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