Biology Reference
In-Depth Information
Genetic Epidemiology of Deafness
WALTER E. NANCE and ARTI PANDYA
1. Introduction
Genetic deafness is a classic example of multilocal genetic heterogeneity in
which a common phenotype can be caused by major genes at a large num-
ber of loci. This insight into the true nature of the phenotype is of rela-
tively recent origin, and the major current emphasis of research has been
on the identification of the specific genes and mutations that contribute to
hearing loss. The molecular approach to the genetic epidemiology of deaf-
ness has been a spectacular success. Nevertheless, a comprehensive under-
standing of the forces that have shaped the temporal and geographic
distribution of deafness phenotypes will require epidemiological data on
secular trends in the incidence of specific phenotypes, as well as knowledge
about the mating structure of the population in question. The goal of this
chapter is to provide a foundation for such an understanding. The model of
multilocus heterogeneity, together with highly specific genetic and envi-
ronmental interactions, is emerging as an explanation for the hereditary
component of deafness. Similar models are likely to be applicable to other
complex diseases.
2. Historical Perspective of the Epidemiology
of Deafness
Deafness has been a familiar part of human experience since the dawn of
recorded history. For example, special provisions and protections were pro-
vided for the deaf in both Roman and Hebrew law (Bender 1970). In China,
Han Yu, the famous historian of the T'ang Dynasty, may have anticipated
the recognition of atypical Usher syndrome by more than a millennium
when he lamented the gradual loss of his sight and hearing before his 50
th
birthday. It was not until the 16
th
century, however, that a Benedictine monk
named Pedro Ponce de Le'on clearly demonstrated the educability of the
deaf. By developing a method of teaching the deaf scions of the Spanish
67
