Genetics may influence men's chances of being homosexual: study

A large study of gay brothers adds to evidence that genes influence men's chances of being homosexual, but the results aren't strong enough to prove it.

Some scientists believe several genes might affect sexual orientation. Researchers who led the new study of nearly 800 gay brothers say their results bolster previous evidence pointing to genes on the X chromosome.

They also found evidence of influence from a gene or genes on a different chromosome. But the study doesn't identify which of hundreds of genes located in either place might be involved.

The new evidence "is not proof but it's a pretty good indication" that genes on the two chromosomes have some influence over sexual orientation, said Dr Alan Sanders, the lead author. He studies behavioural genetics at NorthShore University HealthSystem Research Institute in Evanston, Illinois.

Experts not involved in the study were more sceptical.

Neil Risch, a genetics expert at the University of California, San Francisco, said the data was statistically too weak to demonstrate any genetic link. Risch was involved in a smaller study that found no link between male homosexuality and chromosome X.

The work was published on Monday by the journal Psychological Medicine.

The researchers say they found potential links to male homosexuality in a portion of chromosome X and on chromosome 8, based on an analysis of genetic material in blood or saliva samples from participants.

Chromosome X is one of two human sex chromosomes; the other is chromosome Y, present only in men.

Study participant Dr Chad Zawitz, a Chicago physician, called the research "a giant step forward" toward answering scientific questions about homosexuality and helping reduce the stigma gays often face.

Being gay "is sort of like having certain eye colour or skin colour - it's just who you are," Zawitz said. "Most heterosexuals I know didn't choose to be heterosexual. It's puzzling to me why people don't understand."