Straying mate? It may be in his genes

Men are more likely to be devoted and loyal husbands when they lack a particular variant of a gene that influences brain activity, researchers reported this week.

The finding is striking because it not only links the gene variant, or allele, with the risk of marital discord and divorce, but also appears to predict whether women involved with these men are likely to say their partners are emotionally close and available, or distant and disagreeable, according to the study published in the Proceedings of the National Academy of Sciences.

Two of every five men carry the allele, according to the report.

“Men with two copies of the allele had twice the risk of experiencing marital dysfunction, with a threat of divorce during the last year, compared to men carrying one or no copies,” said Hasse Walum, a behavioral geneticist at the Karolinska Institute in Stockholm, who led the study.

“Women married to men with one or two copies of the allele scored lower on average on how satisfied they were with the relationship compared to women married to men with no copies.”

About 15% of the men without the allele reported serious marital discord in the past year, compared with 34% of men with two copies of the allele. The allele that Walum and a team of scientists studied in a sample of more than 1,000 heterosexual couples regulates the activity of a hormone in the brain known as vasopressin. It dictates how and where vasopressin receptors are situated in the brain.

Larry Young, a psychiatrist who studies the genetics of social behavior at Emory University, said brain receptors in effect act like locks, and vasopressin acts like a key.

The key works only when there is a lock; in the absence of a receptor, vasopressin cannot act.