A McGill University researcher has found a mysterious stretch of DNA that can make men lose their hair.

The discovery could lead to new ways to prevent male pattern baldness or a quick genetic test to determine if a man is likely to hang on to his hair. But it also may help researchers better understand the human genome.

The section of chromosome 20 that Brent Richards and his colleagues have implicated in baldness isn't a gene.

It is in a gene desert, one of the many long stretches of DNA that fill the gaps between the roughly 20,000 genes in the human genome.

Genes carry the codes for the proteins that make up our bodies and keep them healthy.

But no one knows what the vast tracts of DNA in between them do, says Dr. Richards, an assistant professor of genetic epidemiology at McGill and lead author of a paper published yesterday in the journal Nature Genetics.

He and his colleagues are reporting that one section of this mysterious territory on chromosome 20 is somehow linked to receding hairlines and a thinning over the crown.

Men who carry it - as well as another previously discovered gene on the X chromosome - are more likely to become bald.

One in seven men carry both bits of DNA, the researchers found, and they are seven times more likely to lose their hair than men without them.

A second team made the same finding independently, and its work was also published yesterday in the same journal.

The baldness gene on the X chromosome plays a role in how the body uses testosterone.

But now researchers have a new angle to investigate.

The McGill researcher and his colleagues scanned the genomes of more than 500 balding Caucasian men and compared them with those of a similar number of men with full heads of hair.

They found a section of DNA on chromosome 20 that was linked to baldness. They confirmed their findings in a second study involving 1,650 men.

The team didn't patent its results, so there is nothing to stop a company from offering to screen the DNA of customers who want to know what is going to happen to their hair.

"The utility of doing that is questionable in my mind," says Dr. Richards, who at 35 says he is starting to lose his hair.

"One thing I would like to emphasize is that this is not a disease. This is not something most men would be interested in taking precautions for, nor should they."

But there is enormous commercial interest in a treatment for baldness, and several of the collaborators in the study work for the pharmaceutical giant GlaxoSmithKline Inc.

More than $405-million is spent globally every year on treatments for male pattern baldness. Options include two drugs, one that stimulates the hair follicles and another that inhibits the production of a male hormone.

Hair transplants are another possibility, and involve removing tiny plugs of hair and placing them in parts of the scalp that are balding. Male pattern baldness affects one in three men, and there may be other genes or sections of DNA in the human genome that play a role.

Dr. Richards has now joined forces to look for them with the other team that made the same discovery, led by Axel Hillmer at the University of Bonn.

For now, the findings apply only to Caucasian men. Women lose their hair, as well, as they age. But it tends to fall out all over, not in a specific pattern.