Biology Reference
In-Depth Information
Among the 309 HxH matings, 11.7% were consanguineous. If only
“genetic” cases were included (that is, those with a nongenetic etiology, such
as rubella, were excluded from the analysis), the adjusted rate for recessive
pedigrees would have been 13.2%. Chung and Morton (1959) subsequently
analyzed Stevenson and Chessman's data using maximum-likelihood
methods and estimated that the proportions of sporadic, recessive and dom-
inant cases were 0.22, 0.56 and 0.22, respectively. Using the theory of detri-
mental equivalents, they also estimated that genes at 36 ± 12 independent
recessive loci contribute to the phenotype. Rose (1975; 1977) applied
Morton's methods to the 1,722 proband matings and 2,355 proband sibships
in the Fay data set, together with 12,661 nuclear families collected as part
of an Annual Survey of Hearing Impaired Children in 1968, and family his-
tories on 482 students at Gallaudet University. The overall estimates of the
proportions of genetic cases were 0.55 in the Fay data, 0.51 in the National
Survey and 0.76 among the Gallaudet students. Recessive transmission
accounted for 88%, 85% and 78% of the genetic cases respectively. Among
the HxH sibships in the Fay data, the overall and adjusted rates of consan-
guinity were 7.1% and 15.4%. In the two large nationwide data sets, which
were collected 100 years apart, the estimated proportion of genetic cases
was remarkably consistent, even though the latter is known to have
included a large cohort of patients with rubella deafness. The higher pro-
portion of genetic cases, and cases showing apparent dominant transmis-
sion among the high-achieving Gallaudet student population, is of interest.
Most of these students have at least one deaf parent, and at home as well
as at Gallaudet ASL was probably the language of choice. Thus, as might
be expected, a familiar language and culture facilitate academic excellence.
Fay's data set included 1,299 in which both parents were deaf. Among
these, the estimated proportion of non-complementary matings (that is,
those that can produce only deaf offspring) was 0.042 ± 0.007, while the
estimated proportion of complementary matings (that is, all offspring are
hearing) was 0.875 ± 0.17. Non-complementary matings refer to those
between individuals with the same type of genetic deafness, while comple-
mentary matings refer to those between individuals with different types of
genetic deafness. Genetic analyses of other large data sets have been
reported by Macklin et al. (1946), Sank (1969), Chung and Brown (1970),
Furusho (1957), Mori (1959), Marazita et al. (1993) and Liu et al. (1994).
The study by Liu et al. (1994) is particularly noteworthy because it involved
a clinical survey of 126,876 individuals drawn by a stratified random sam-
pling procedure from the 104 million citizens of Sichuan province in China
in 1986 to 87. In the sample, 236 individuals were found to have a hearing
loss of 90 dB or more. The overall prevalence of profound deafness was 0.82
per 1,000 and ranged from 0.7 per 1,000 in the predominant Han ethnic
group 0.0 among 2,933 Tibetans, to 6.6 per 1,000 among 1,968 members of
the Lisu minority group. The prevalence ranged from about 0.5 per 1,000
for subjects less than 30 years of age, to a high of 1.8 per 1,000 for those
