By Keay Davidson

　　Friday, December 24, 2004

　　Scientists studying a deadly skin cancer have inadvertently found a possible explanation for why hair turns gray.

　　But don't throw out that hair dye. By itself, the finding does not immediately point to a way to prevent graying hair, caution the Boston scientists who made the discovery. Moreover, the researchers said they're more interested in curing cancer.

　　The finding, published Thursday in Sciencexpress, the online journal run by Science magazine, was an unexpected spin-off of research on melanoma, the deadliest form of skin cancer. The researchers found that hair begins to turn gray when the pigment-producing cells in skin and hair —— also involved in melanoma —— start dying off.

　　"Preventing the graying of hair is not our goal," said one team member, oncologist Dr. David E. Fisher of Dana-Farber Cancer Institute. "Our goal really is to kill melanoma," he said. But "at this point we still are very early" in our understanding of melanoma, he said.

　　Melanoma is the most serious form of skin cancer, one that causes almost 8,000 deaths a year in the United States. Overexposure to the sun is a major cause of melanoma, and the disease is known to be particularly resistant to chemotherapy and radiation.

　　Still, the scientists' discovery is a reminder of how one of life's most familiar and usually lamented events —— the graying of hair —— lacked a clear-cut scientific explanation until now.

　　"Hair graying is the most obvious sign of aging in man, yet its mechanism is largely unknown," the scientists wrote in their paper.

　　The other authors are dermatologist Dr. Emi K. Nishimura, also of Dana-Farber, and pathologist Dr. Scott R. Granter of Brigham and Women's Hospital in Boston.

　　Historically, some scientists have blamed gray hair on causes that range from stress to genetic factors to smoking and thyroid imbalances. There are many anecdotes about people whose hair suddenly turned white, but experts have debated the causes.

　　One proposed explanation for overnight graying is that during a time of extreme psychological stress, the body uses all its available energy on essential life-preserving functions —— for example, keeping the immune system in tip-top shape. During such crises, the body doesn't waste energy on less vital needs, such as hair color, or so the theory goes.

　　The research described Thursday supports the idea that premature graying is at least partly genetic.

　　Originally, the scientists were studying melanomas in mice. Melanoma is the malignant form of cells called melanocytes, which generate the pigments that color hair and skin. In healthy people, melanocytes help protect the skin, but in people with melanoma, they grow uncontrollably.

　　The scientists wondered whether they could find vulnerabilities that could be exploited to stop the cancerous growth. In particular, they focused on a gene called Bcl 2, known to keep melanocytes healthy. If they could find a way to interrupt the gene's actions, perhaps they could block the growth of melanomas.

　　To study the Bcl 2 gene's effect, the scientists raised mice that lacked it. The result was unexpected: The animals' hair grayed soon after they were born. Thus, the scientists propose, a mutated version of the Bcl 2 gene may cause premature graying of hair in certain people.

　　The scientists were also interested in the relationship between the hair graying and the number of adult stem cells that replenish the body's supply of the pigment-producing cells. Both mice and humans have reservoirs of these adult stem cells.

　　Indeed, they found that the grayer the hair in the mice, the fewer the surviving stem cells. This reinforces their proposal that the loss of melanocyte-producing stem cells contributes to graying.

　　In any case, hair color isn't the oncologists' main concern. And although the group has ideas about how to block growth of melanoma, the distance from today's knowledge to a cure for the cancer is "a fairly big hurdle," Fisher said.