In a report in Friday's issue of Science, University of Western Ontario scientist George Rice and his colleagues found no evidence that gay brothers shared a set of DNA sequences on a region of their X chromosome called Xq28. The earlier study, by National Cancer Institute chief geneticist Dean Hamer, found that 33 out of 40 pairs of gay brothers shared five DNA sequences on Xq28. It was published in Science in 1993. Rice looked at four sequences on Xq28, one from Hamer's study and three new ones, in a slightly larger group of gay brothers. They found no excess sharing for any of the markers.
Brothers normally share about half their DNA on any chromosome.
Rice's results counter Hamer's and do not support an X-linked gene passed from the mother to the gay brothers. We could not corroborate a gene linkage on the X chromosome. Hamer said study methodologies may account for the difference in results in the Rice study. Hamer said two other studies, one published in Nature Genetics in 1995 and another presented at the American Psychiatric Association meeting in Toronto, Canada, in 1998, support his earlier findings. Hamer said he is continuing to look at other genes at the DNA level.