Mapping DNA Turns Controversial

By Donna Alvarado & Jim Puzzanghera
San Jose Mercury News
(E-MAIL: letters@sjmercury.com)

The largest annual gathering of geneticists last week only reinforced the belief that scientists are moving at break-neck speed in the quest to decode nature's most complicated puzzle - the location and biological tasks of the 3 billion componets in human DNA.

For four days at the Moscone Center, the American Society of Human Genetics presented the results of more than 2,400 research projects. And it became clear that researchers are closing in on genetic links for everything from fatal diseases to traits as diverse as obesity and homosexuality.

''Progress has been enormous,'' said Charles Epstein, the society's president and a top geneticist at the University of California, San Francisco. ''I think we can only guess where we'll be . . . when the 20th century ends.''

But in his presidential address to 4,000 colleagues, at the meeting, Epstein delivered a warning - be careful not to overhype your research.

''Not everyone believes genetics is God's gift to mankind,'' he said. ''Our own hyperbole is part of the cause.''

'Gay gene' provides riveting discussion

Nothing combines the social and scientific implications of genetics more than the question of whether a gene determines homosexuality.

Since the reported discovery of the so-called ''gay gene'' in 1993 by a geneticist at the National Institutes of Health, the scientific community has questioned its validity while ethicists have grappled with the potential ramifications of the findings.

There was some of both at the meeting during a standing-room-only workshop on the genetics of homosexuality. While there is little doubt that homosexuality is at least partly genetic, there is much doubt that a single gene or even several genes are the sole determining factor.

''Overall at this point in time, the genetic evidence is unclear,'' said Neil Risch, a genetics professor at Stanford University.

Studies on twins, a standard early step to determine a genetic link, have shown evidence of inheritance patterns in homosexuality, but in varying ways.

Mutation is linked to rare sex reversals

Some people are born with a male genetic code, yet have ovaries and other female characteristics. Others, called hermaphrodites, are born with a combination of female and male sex organs, or ovotestes.

Scientists are studying whether particular gene mutations account for some of these rare occurrences. So far, they have found mutations in two genes, called ''sry'' and ''sox9,'' that together may account for about 15 percent of those with male genetic codes but female characteristics, said Andrew Sinclair at the University of Melbourne, Australia.

Sinclair studied babies born with a rare condition called familial campomelic dysplasia and found that they had the conventional ''XY'' male sex chromosomes, but showed female sex characteristics. Most died within six months of birth of other medical problems associated with the condition.

These sex-reversed babies all had a mutation in the sox9 gene. In one family, Sinclair found three offspring with XY chromosomes but female sex organs: two had ovaries and one had combination male/female ovotestes. He traced the mutation to the father, who had an unusual mosaic pattern in his own sex chromosomes.

Others have done studies finding mutations in genes that regulate the sensitivity of body cells to hormones such as testosterone. Some of those people also have XY chromosomes but, because their cells are insensitive to testosterone, they develop female sex characteristics.

Sinclair said there are probably other gene mutations not yet known that could explain some of these sex reversals and other similar conditions.

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