Abolition of inbreeding laws is urged Researchers raise doubts on risks

February 15, 1993|By Los Angeles Times

BOSTON -- Marriages between cousins and other close relatives are becoming more common in the United States and other Western countries as a result of immigration from countries where such marriages are accepted practice, scientists said here yesterday.

Several new studies suggest that the adverse genetic consequences of such inbreeding are real but are much less serious and widespread than is generally believed, researchers reported at a meeting of the American Association for the Advancement of Science. "There are ill effects, but they've probably been exaggerated in the past," said geneticist James V. Neel of the University of Michigan.

These marriages, called consanguineous, are now prohibited in 30 states and carry heavy criminal penalties in nine. But the small increases in mortality resulting from them "don't warrant such heavy-handed legislation," said geneticist Alan Holland Bittles of the University of London.

Laws against inbreeding should be abolished, he said, and Mr. Neel agreed.

"Those laws were not passed for biological reasons," Mr. Neel said. "There was some religious motivation."

An estimated 20 percent of marriages worldwide are between individuals who are first cousins or more closely related, with the incidence rising as high as 50 percent in countries such as Pakistan, Mr. Bittles said.

Such marriages play an integral part in the conservation of cultural values and property, he noted.

Inbreeding is not biologically hazardous in and of itself, but rather for the fact that it brings out the effect of deleterious genes that might have otherwise gone unnoticed. Of the estimated 100,000 genes in each human, scientists now believe that as many as 60 are defective. Most such defects are "recessive" -- they don't produce any ill effects because the individual also inherited a good gene from the second parent.

But when two people with the same recessive gene mate, one of every four children will get two copies of the bad gene and develop the associated disorder. Recessive genes can cause fatal disorders early in life and can also cause such disabilities as congenital blindness, congenital deafness and mental retardation.

Mr. Bittles has been studying the effects of consanguineous marriages in developing countries. In Pakistan, for example, he found that 16 percent of children from unrelated marriages died by age 10, while 21 percent of those from consanguineous marriages died by the same age.

Geneticist Lynn B. Jorde of the University of Utah has taken advantage of the abundant genealogical records among that state's Mormon population to study the problem. Among 405,595 members of the faith studied, 5,714 were the products of consanguineous marriages.

He found that among unrelated parents, 13 percent of the children died by age 16, compared to 22 percent of those resulting from consanguineous marriages. He noted that the death rates were high because the records extend back more than 100 years. Current death rates are much lower, he said, but the relative proportions remain the same.

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