A cure for baldness has come a step closer after scientists identified a gene that is connected to hair loss. The breakthrough should help scientists develop new treatments as well as help pinpoint early in life which men are likely to lose their hair.
The Sox21 gene has in the past been shown to be linked to the formation of nerve cells, but the new study is the first to indicate its function in ensuring hair retention.
Researchers made the finding during experiments on mice which, like humans, carry the gene.
The scientists blocked the activity of the gene in mice and found that the rodents started losing hair on their heads about 15 days after birth and became completely naked a week later.
"It is entirely possible that the gene is also a cause of thinning hair among humans", said Professor Yumiko Saga at the National Institute of Genetics in Tokyo.
Hairs have a long growing phase - two years or more - followed by a short resting phase of two or three months.
But as some men age this pattern gradually reverses until eventually the resting period is so long that there's no new hair coming through to replace the 100 to 150 hairs we lose daily through natural shedding.
The Japanese reseachers, who published their findings in the Proceedings of the National Academy of Sciences, believe that Sox21 governs this cycle.
"Normally, new hair appears right after old hair falls out," said Professor Saga. "But the hair of these mice fell out very early, making their bald periods longer."
Dr Bessam Farjo, medical director of the Institute of Trichologists, said the research added to the growing knowledge of hair loss and could help identify and target young men who will lose their hair.
"It is very interesting," he said. "It should help in the current research into finding a cure for hair loss. It will also help us accurately target men likely to lose their hair so we can treat them before it happens."
Hair loss affects an estimated 7.4million British men. There is no cure but several tablets and lotions claim to have a preventive effect and help regrowth.
By the age of 60 more than two thirds of men are affected by it.