to a study linking a common male gene to relationship problems.

　　The gene variant, which is present in four of 10 Swedish men, can explain why some men are more prone to stormy relationships and bond less to their wives or girlfriends, a team of researchers at Stockholm's Karolinska Institute said.

　　"There are, of course, many reasons why a person might have relationship problems, but this is the first time that a specific gene variant has been associated with how men bond to their partners," Hasse Walum, one of the researchers, said in a statement.

　　The team found that men who carry one or two copies of a variant of the gene often behave differently in relationships than men who lack the gene variant, called allele 334.

　　Men who had two copies of allele 334 were twice as likely to have had a marital or relationship crisis in the past year than those who lacked the gene variant, the statement said.

　　Their wives or girlfriends also noticed the difference.

　　"Women married to men who carry one or two copies of allele 334 were, on average, less satisfied with their relationship than women married to men who didn't carry this allele," Walum said.

　　The study surveyed 550 twins and their partners or spouses in Sweden.

　　Martin Ingvar, a professor of neurophysiology at Karolinska Institute, said the results were "very exciting."

　　"These are original findings which shed light on the fact that all of our behaviours are influenced by both nature and nurture. Even complex, cultural social phenomens such as marriage are influenced by a person's genetic make-up," Ingvar said.

　　The same gene has previously been linked to monogamous behaviour in male voles, a mouselike rodent.

　　The results of the study were published Tuesday in the US scientific journal Proceedings of the National Academy of Sciences