Hillmer, together with other researchers in Germany and Australia, genotyped several hundred men who began to go bald before the age of 40. They found five variants on chromosome 20 that were strongly associated with male pattern baldness.
“Our aim is eventually to identify all the genes that are involved,” Hillmer says.
In another study of nearly 2,000 balding men and women, researchers from Europe, Canada, and the United States also identified a link between variants on chromosome 20 and male pattern baldness. One in seven of the Caucasian men in that study had risk factors on both that chromosome and the X chromosome; they were seven times likelier to go bald than people without those variants. The effects of the same risk factors in women were less pronounced. Neither of the research groups found any evidence of interactions between genes at the two locations.
The prevalence of these genetic risk factors for baldness “varies strikingly worldwide,” Hillmer says, although it doesn’t fully explain geographic differences in the prevalence of male pattern baldness, such as the low incidence among Southeast Asians.
A separate study by researchers in Europe offers new insights into the functioning of hair follicles, at least in mice. It was previously thought that stem cells in hair follicles were limited to a specific part of the follicle, and that they seldom divided. But Rune Toftgård of the Karolinska Institute, in Sweden, and his colleagues discovered long-lived stem cells in mouse hair follicles that are very active. Elaine Fuchs, head of the laboratory of mammalian cell biology and development at The Rockefeller University, who wasn’t involved in the study, termed Toftgård’s research “compelling.”
“Even when they’re out of their normal location, they still have stem-cell properties,” Toftgard says.
When the researchers isolated these cells and transplanted them onto the skin of hairless mice, the cells regenerated into complete follicles, which sprouted hair. While that might seem like a promising approach for filling in thinning human hair, Lloyd E. King of Vanderbilt University, who wasn’t involved in the work, says that human and mouse follicles are different enough that such treatments are “unlikely to happen soon.”