Sexual orientation and genetics: X marks the spot

Here is the abstract of a new report from Human Genetics about a link between some moms and the sexual orientation of sons. This kind of stuff is interesting of course but the conclusions drawn by the researchers is speculative: “The research “confirms that there is a strong genetic basis for sexual orientation, and that for some gay men, genes on the X chromosome are involved,” said study co-author Sven Bocklandt, a postdoctoral researcher at the University of California at Los Angeles.” The findings I read in the abstract do not “confirm” anything. Furthermore, the study as described could not provide any pathway from a putative genetic mechanism to behavior. All they have shown is there are group differences.

As I look at it, none of this is very enlightening unless the temperament and environment of the sons is also taken into consideration. There are potential intervening variables that are not even considered by these researchers (e.g., gender atypical temperaments). GAT may be related to these changes in the X chromosome but I doubt this was taken into account.

Human Genetics
Issue: Volume 118, Number 6
Date: February 2006
Pages: 691 – 694
Extreme skewing of X chromosome inactivation in mothers of homosexual men
Sven Bocklandt, Steve Horvath, Eric Vilain and Dean H. Hamer

Abstract Human sexual preference is a sexually dimorphic trait with a substantial genetic component. Linkage of male sexual orientation to markers on the X chromosome has been reported in some families. Here, we measured X chromosome inactivation ratios in 97 mothers of homosexual men and 103 age-matched control women without gay sons. The number of women with extreme skewing of X-inactivation was significantly higher in mothers of gay men (13/97=13%) compared to controls (4/103=4%) and increased in mothers with two or more gay sons (10/44=23%). Our findings support a role for the X chromosome in regulating sexual orientation in a subgroup of gay men.