- WASHINGTON (CP) -- Researchers at the University of Western Ontario are
questioning a U.S. study that said a gene inherited from mothers influences
men's sexual orientation. In 1993, Dr. Dean Hamer and colleagues at the
U.S. National Cancer Institute provoked a worldwide furor when they reported
they had found evidence of a "gay gene" in men.
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- They had studied 40 pairs of gay brothers
and found 33 of them shared a particular sequence of the genetic codes
on their X chromosomes, in an area called Xq28. They said that pointed
to a possible gay gene. But in a study published in this week's Science,
George Rice and colleagues at Western in London, Ont., said they studied
more pairs of gay brothers and found no evidence that they shared some
sort of mutation in that area.
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- "These results do not support an
X-linked gene underlying male homosexuality," Rice's team wrote in
its report. But the team added that the search should continue for any
possible genetic cause of homosexuality. Men, in addition to their 22
pairs of matched chromosomes, have one X and one Y chromosome. Women have
two Xs.
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- Men inherit their X chromosomes from
their mothers, and because they have just one copy, are vulnerable to
genetic defects carried on the X chromosome such as colour blindness and
Fragile X syndrome, which causes a form of mental retardation.
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- Hamer's team had noted a tendency for
homosexuality to run in the female line -- men whose mothers had gay brothers
also tended to be homosexual, the team reported. So it looked for an area
on the X chromosome that might be involved.
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- The team homed in on an area known as
Xq28.
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- Rice's team tried to duplicate and expand
on those results, studying 52 sets of brothers in Canada who were both
gay, looking specifically at the Xq28 gene. "We advertised in Canadian
gay news magazines for families in which there were at least two gay brothers,"
the team wrote.
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- It compared their genes to samples taken
from 33 pairs of brothers who had been gene-tested for multiple sclerosis.
But the researchers did not find any particular variation of the gene
that marked gays from non-gays. Gay brothers were not unusually likely
to share one of four variations of Xq28 that they looked for.
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- "It is unclear why our results are
so discrepant from Hamer's original study," the team wrote. The researchers
said it was possible there was another "gay gene," as the team
only looked at one gene for its study. But Rice's team also said that
if homosexuality was a simple inherited trait, it would be very likely
to have been bred out -- because homosexuals would be less likely to have
children and pass on the trait.
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- But studies dating back to the 1980s
show some evidence that homosexuality might run in families.
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- One study on identical twins, who share
more of their genes than regular siblings, found one twin was more likely
to be gay if his twin was, and another study found homosexual men were
more likely to have homosexual brothers even if they were not twins.
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- Other experts point out that being homosexual
does not preclude having children, so there would be no reason for a "gay
gene" to have been bred out.
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