Most men and many women have some hair loss by their 70s or 80s.
But the telltale loss of hair at the crown and temples, known as male-pattern baldness, starts as early as the 20s in about 20% of men. It's apparent in about 40% of men in their 40s and 60% of men in their 60s.
What happens on the scalp is that testosterone combines with an enzyme called 5-alpha reductase to form dihydrostestosterone, or DHT, which causes hair follicles to shrink and become more sparse.
A study in 2004 found that men whose fathers had male-pattern baldness were 2.5 times as likely to have some level of hair loss than men whose fathers did not. Two recent studies scanned DNA samples from large groups of men with male-pattern baldness and looked for genetic markers they had in common that weren't present in control groups with abundant hair.
Researchers at Bonn and Dusseldorf universities, and a second group from McGill, London's King's College and GlaxoSmithKline PLC, both identified variations on chromosome 20. An androgen-receptor gene (labeled AR) on the X chromosome is common to many bald men. Men inherit a single X chromosome from their mothers.
The gene variation for balding is neither dominant nor recessive, but additive, says Markus M. Nothen, a University of Bonn geneticist and the lead author of one of the studies who also helped discover the AR gene on the X chromosome. Men with one affected copy were 3.7 times as likely to show early hair loss, and those with two copies were 6.1 times as likely.
The McGill study calculated that about one in seven Caucasian men have both the chromosome 20 variation and the AR gene, which increases their risk of early baldness sevenfold.
Experts agree that treatment for hair loss is more effective if started early. Only two drugs are approved for baldness in the U.S.--minoxidil ( Rogaine ) and finasteride ( Propecia ). When the cream and pill, respectively, are used together, dermatologists say, they can slow hair loss for several years.
Source: Health Journal, The Wall Street Journal, October 14, 2008