NEW YORK (AP) - In a finding that may someday help scientists understand and treat ordinary baldness, researchers say they've identified a normal role for a gene that causes two rare hair-loss disorders when it's disabled.

So far, even with the new work, there's no evidence of a direct link between the "hairless" gene and typical baldness. In fact, the new work doesn't even explain why the gene causes the rare hair-loss disorders when it malfunctions.

But many types of hair loss probably share a similar biological mechanism, and understanding the hairless gene's function will help scientists figure that mechanism out, said researcher Catherine C. Thompson.

Thompson, from the Kennedy Krieger Research Institute and the Johns Hopkins University School of Medicine in Baltimore, and colleagues report their study of the hairless gene in the Oct. 15 issue of the journal Genes and Development.

Previous work has shown that people who inherit a malfunctioning version of hairless can get an extreme form of a condition called alopecia universalis, in which eyebrows, eyelashes and body hair fail to develop. Babies are born with scalp hair, but it fails to regrow after being shaved, as is the custom in the Pakistani family in which the gene was identified.

Other work has shown that a malfunctioning hairless gene can cause another hair-loss disorder, called papular atrichia.

Thompson's work investigated the function of the protein that cells normally make with instructions from the hairless gene.

Results suggest that it helps regulate genes that are activated by thyroid hormone. The hairless protein acts to shut those genes down when thyroid hormone is absent, researchers concluded.

Thompson said the hairless gene itself is activated by thyroid hormone, so it may influence its own activity as well as that of other genes targeted by the hormone. It may be a key factor in the hormone's effects in both brain and skin, she said.

Angela Christiano, who studies the biology of inherited hair disorders at Columbia University, praised Thompson's work and agreed it's not obvious what the results mean for hair loss.

Christiano is also studying the hairless gene. She said she's optimistic about finding a natural target of the hairless protein in the skin, which could be a step closer to discovering a link to hair loss.

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