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Study Links Gene Variant in Men to Marital Discord

Seventeen percent of the men without the allele were living with women without being married to them, compared with 32 percent of men with two alleles doing so.

The study was published in the Proceedings of the National Academy of Sciences.

Young praised the study, saying it extends a remarkable series of animal experiments he and other scientists conducted some years ago. They showed that the distribution of vasopressin receptors in the brain appears to predict why males and females form lifelong pair-bonds in one species but not in another.

The studies focused on two species that look nearly alike: prairie voles and montane voles. The first time a male prairie vole mates with a female, he forms a bond with her for life, breeding and raising successive litters. Male montane voles think of sex as a series of one-night stands; they are loners and do not bond with females or help raise offspring.

Young and others concluded that the difference between these species is because of the same gene variant that Walum studied. In the kind of experiments that cannot be replicated in humans, Young and others also showed that manipulating vasopressin receptors in vole brains can turn loner voles into devoted partners and fathers, and vice versa.

No one knows for sure whether the same mechanism is at work in humans. Although humans are evolutionarily distant from voles, there are many examples in nature that show that the action of genes is conserved across distantly related species. In the monogamous voles, Young said, bonding between animals seems to trigger vasopressin action in the brain's reward circuits. Not surprisingly, this prompts the animals to seek to bond with each other.

Geert J. de Vries, a neuroscientist at the University of Massachusetts in Amherst who studies vasopressin, hailed the new study and said it dovetails with work he and others have conducted that show vasopressin seems to play a much larger role in the brains of men rather than women. Beyond the immediate study on monogamy -- vasopressin seems to change how men, not women, behave in long-term relationships -- De Vries said there could be intriguing links between the Stockholm study and research into the causes of disorders such as autism.

"If you look at what is most prominent in kids with autism, the big difference is in social behavior," said De Vries, as he pointed out that autism is far more common in boys than in girls. "In this study, they are looking at social behavior related to marital status and the way men and women interact . . . you could imagine variability in these alleles can contribute to autism."

All the scientists emphasized that more work needs to be done to replicate the finding, and to explore possible interactions between multiple genes and environmental factors. Partnerships in marriage and long-term relationships, moreover, involve many dimensions of behavior -- sexual desire, romantic love and the loyalty that Walum's study focused on.

"What this means is that some people will go into marriage with a stronger deck of cards," Fisher said. "But there are people genetically prone to alcoholism who give up booze and make a good marriage. No one is saying biology is destiny."

Fisher, who described herself as a romantic, said she would not reject a potential mate who has two copies of the risky allele. She paused, then added: "But I might not start a joint bank account with them for the first few years."

Staff writer Rob Stein contributed to this report.

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