Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: TUESDAY, October 31, 1995 TAG: 9510310103
SECTION: NATIONAL/INTERNATIONAL PAGE: A-3 EDITION: METRO
SOURCE: Associated Press
DATELINE: NEW YORK LENGTH: Medium
Scientists have found new evidence that a gene inherited from mothers helps influence whether a man is homosexual, bolstering a study that made headlines in 1993.
``Our result says that genes are involved in male sexual orientation, although they certainly do not determine a person's sexual orientation,'' said Dean Hamer, an author of the study.
``There probably are other biological factors, like hormones, and other variables we simply don't know anything about yet.''
The study follows others that have suggested a biological influence in sexual orientation, but scientists still can't explain what makes a person homosexual, heterosexual or bisexual.
The latest study does not identify a specific gene. But like Hamer's 1993 study, it suggests such a gene resides in a particular region of the X chromosome, one of the microscopic thread-like structures that carry genes. Men inherit the X chromosome from their mothers.
Hamer said there was no way to know how strongly the gene influences the development of homosexuality in men. Researchers looked for such an effect in women but found no evidence for it.
Hamer, a researcher at the National Cancer Institute, reports the work in the November issue of the journal Nature Genetics with colleagues at the institute, the University of Colorado and the Whitehead Institute for Biomedical Research in Cambridge, Mass.
Dr. Elliot Gershon, chief of the clinical neurogenetics branch of the National Institute of Mental Health, said the work does not prove such a gene exists in the chromosome segment, but it is suggestive.
The study focused on a region of the X chromosome that had been identified by the 1993 study.
In a man, this region can get its genetic material from either of his mother's two X chromosome versions. As a result, two brothers normally have about a 50-50 chance of sharing the same version of the genetic material within this region.
Hamer and colleagues examined 32 pairs of exclusively or mostly homosexual brothers from unrelated families. Twenty-two pairs, or two-thirds, shared the same version of the genetic material, suggesting that it contains a gene predisposing to homosexuality.
By the same logic, Hamer said that if gay brothers shared a version containing a homosexuality gene, then any heterosexual brother of theirs probably would have a different version. The study showed that was the case in nine of 11 families studied.
Hamer said that by focusing on families with two gay brothers, the researchers were more likely to find a genetic effect on homosexuality than if they studied a broader population.
``This study is an important addition to the growing body of evidence indicating a biological basis for homosexuality in some people,'' said Beth Barrett, spokesperson for the National Gay and Lesbian Task Force.
by CNB