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To bond or not to bond may depend on common hormone gene variant: vasopressin receptor may contribute to commitment phobia.

There's news for women who want a man who bonds rather than a James Bond: Scientists have identified a genetic variation that appears to weaken a man's ability to emotionally attach to one partner.

The study, published online September 2 in the Proceedings of the National Academy of Sciences, is the first to try to examine whether a hormone that encourages monogamy in animals plays a similar role in male humans. Before ordering a DNA-fidelity test, though, women should consider that the study wasn't designed to determine whether the gene in question is responsible for monogamy in humans.

"We can't with any accuracy predict effects on behavior," says Hasse Walum of the Karolinska Institute in Stockholm. "A lot of different things determine how happy you will be in a relationship." But women can now wonder, "What about his vasopressin la receptor subtype?"

The hormone vasopressin affects several body systems, including cardiac and urinary function. In addition, scientists have long studied how vasopressin influences behavior in prairie voles. The mouselike animals, found in the grasslands of North America, are famous for social monogamy. Males tend to be family guys, sticking close to home and helping to raise the pups.

Over years of study, scientists have concluded that prairie vole bonding has much to do with vasopressin activity in the brains of males. Scientists have even manipulated vasopressin levels in the vole brain, making the animals more, or less, faithful. Vasopressin is not a love potion, though. Nerve cells also must be equipped with specific receptor molecules that allow the hormone to bind to the cells and activate certain internal circuitry.

The new study examined a gene that codes for a vasopressin receptor in the human brain. Walum and an international team of collaborators also asked about 550 couples, who had been together at least five years, to fill out questionnaires measuring their level of "pair-bonding" and marital strife.

In the end, one common variation of the gene, called the 334 allele, was associated with lower scores on partner bonding and greater odds of marital conflict, especially in men. Among men with either no copies or just one copy of the 334 allele, about 15 percent reported a marital crisis in the past year. When men had two copies of the 334 allele, the odds of marital crisis jumped to 34 percent.

"This is actually a real breakthrough paper," says Steve Phelps of the University of Florida in Gainesville. "The magnitude of effect is really astonishing." But he and others were also cautious.

"The results are really intriguing," says Larry Young of Emory University School of Medicine in Atlanta, who in 2005 reported in Science that, in male voles, a variation of the same gene predicted the quality of pair-bonding. "I still remain skeptical until this can be replicated."
Commitment and the 334 Allele in Men

 Percent married Percent experiencing
 (vs. cohabiting only) marital crisis or threat
 of divorce

0 83% 16%
1 84% 16%
2 68% 34%

A particular gene variant seems to
pre-dispose men to relationship issues.

Note: Table made from bar graph.
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Article Details
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Author:Beil, Laura
Publication:Science News
Geographic Code:1USA
Date:Sep 27, 2008
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