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 Findings from the study, which has yet to be published or reviewed
in detail by other scientists, were presented at a meeting of the
American Society of Human Genetics in Baltimore.
It followed 37 pairs of identical male twins in which one was
homosexual and one heterosexual, and 10 sets of twins in which both
males were homosexual. The study found that the presence of specific
epigenetic marks in nine areas of the human genome could predict
homosexual preference with up to 70 percent accuracy.
The epigenome is sometimes described as molecular "switches" that
can turn on or silence individual genes in DNA. Scientists believe
epigenetic differences can be influenced by environmental and
lifestyle factors, from exposure to chemicals to parental nurturing.
 "To our knowledge, this is the first example of a predictive model
for sexual orientation based on molecular markers," Tuck Ngun, lead
researcher on the study from the David Geffen School of Medicine of
the University of California, Los Angeles, said in a statement.
Genetics experts who critiqued the findings said it was premature to
draw any conclusions on the predictive powers of epigenetic markers.
"The question as to whether that prediction is going to be useful
outside of the small number of twins in the study is really
unclear," said Dr. Christopher Gregg, a genetics professor at the
University of Utah.
Others noted the small size of the population studied and stressed
that such findings often fall apart when applied to larger groups of
people.
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"One thing you can clearly see is that the sample size is too small.
They don't have enough power to make that claim," said Dr. Peng Jin,
professor of human genetics from Emory University in Atlanta, who
attended the meeting in Baltimore.
"What they are seeing may be certain correlations, but I don't think
they have what they claim, which is a predicting model," he added.
"It's definitely an interesting observation, but ... I don't want
the general audience to misinterpret whatever they are presenting,"
Jin said.
Gregg said he was impressed by the UCLA team's "state-of-the-art"
methodology, but said much larger studies must be undertaken to
reach any conclusions.
"Just because there is something different doesn't mean that's
what's causing people to behave one way versus the other," he said.
(Reporting by Bill Berkrot; Editing by Dan Grebler)
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