University of Illinois at Chicago
Institute for Juvenile Research
Department of Psychiatry (M/C 747)
1747 W. Roosevelt Road
Chicago, IL 60608, USA
FOR IMMEDIATE RELEASE:

FIRST GENOME SCAN OF MALE SEXUAL ORIENTATION PUBLISHED

CHICAGO, Illinois, USA, January 12, 2005

A new genetic study helps explain why some men are gay and other men are heterosexual. The first
research project that examines linkage between male sexual orientation and genes across the human genome was published this month in the prestigious biomedical journal, Human Genetics. The culmination of several years of research, the report identified three new chromosomal regions of interest.

One hundred forty-six families that had two or more gay brothers participated in the study. The largest finding was a statistically suggestive linkage to a region on chromosome 7 called 7q36, and the second largest link was found on chromosome 8, in a region called 8p12. There was also an interesting finding on chromosome 10, in the region called 10q26, where the linkage to sexual orientation only occurred if that region was
inherited from the mother. This is likely a result of the recently discovered phenomenon that geneticists call 'genomic imprinting.' Given the complex nature of sexual orientation it is not surprising that multiple genetic regions were implicated.

According to the lead author of the study, Dr. Brian Mustanski, "Our study helps to establish that genes play an important role in determining whether a man is gay or heterosexual. It expands upon previous research with twins, which has consistently found evidence for genetic influences on sexual orientation. The next steps will be to see if these findings hold up in a new sample and then identify the particular genes within these newly discovered chromosomal regions." Dr. Mustanski emphasized that finding the specific genes would have implications beyond uncovering the cause of homosexuality. Their identification would also greatly advance our understanding of human variation, evolution, and brain development.

Previous genetic research had focused on the X-chromosome, which men inherit only from their mothers, because of the tendency for homosexuality to pass through the mother's side of the family. When the scientists
used their new genetic markers, they confirmed linkage to the X chromosome in the previously studied families of this sort, but not in new families with different patterns of inheritance. This pattern of findings suggests that different genes may influence sexual orientation in different families, a process referred to as locus heterogeneity.

The study was conducted at the National Institutes of Health in the laboratory of the senior author, Dr. Dean Hamer. Researchers in the laboratory of Dr. Nicholas Schork at the University of California at San Diego provided statistical consultation on the project. Dr. Brian Mustanski is currently at the University of Illinois at Chicago. The study was published in the online version of Human Genetics on January 12, 2005 and will be in print in an upcoming issue of the journal.

For more information please contact Dr. Brian Mustanski, at 312-996-9505 or bmustanski@psych.uic.edu. The article can be downloaded from the publisher at
http://springerlink.metapress.com/openurl.asp?genre=article&id=doi:10.1007 /s0043 9-004-1241-4