| Did sign language increase deaf population?
Wednesday, April 28, 2004 Posted: 1:22 PM EDT (1722 GMT)
WASHINGTON (Reuters) -- Sign language may have helped make deafness more common in the United States because it allowed deaf people marry other deaf people, U.S. researchers said.
A computer simulation showed a high rate of marriage among deaf people could have caused a doubling of rates of genetic deafness seen in the past 200 years -- since a coordinated system of sign language was developed.
Intermarriages among the deaf started to increase about 1800 after the first schools to teach sign language were opened, improving the social and economic status of the deaf and allowing them to communicate more easily.
Many deaf people prefer to marry other deaf people and prefer also to have deaf children.
"In the United States, at least 85 percent of individuals with profound deafness marry another deaf person," said Dr. Walter Nance, a professor of human genetics at Virginia Commonwealth University who led the study, which was released Tuesday.
"Because we now know that more than 100 different genes are responsible for deafness, most deaf parents have children with normal hearing because they pass different genes to their offspring," he added in a statement.
But writing in the June issue of the American Journal of Human Genetics, Nance and colleagues said intermarriage could eventually cause a variation of a gene called connexin, which causes deafness, to become more common.
"In the case of marriages among couples who both have the same form of recessive deafness, all their children will be deaf and capable themselves of also passing on the altered gene to their offspring," Nance said.
In addition, as much as 3.5 percent of the entire population of the United States may carry single mutations involving the connexin gene, making it one of the most commonly recognized single gene defects, he said.
The findings may help shed light on how humans acquired language -- spoken and otherwise, Nance said.
"When you think about how the onset of selective marriages among deaf populations led to an increase in specific mutations for deafness, you easily can see how these same forces might have contributed to the spread of genes for speech among Homo sapiens 160,000 years ago," Nance said.
"If you were one of the first primates with an ability to communicate by speaking, wouldn't you want to select a partner who could whisper sweet nothings in your ear?"
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