Some men who carry two genetic variants may have a sevenfold increased chance of showing male pattern baldness, international researchers have found.

In Sunday's issue of the journal Nature Genetics, two teams of researchers described the predisposition to male pattern baldness — the most common form of baldness, usually involving hair loss above the temples and at the crown of the head.

Male pattern baldness affects about one-third of men by age 45. Hair loss takes a social and economic toll for some, with hair transplants in the U.S. alone costing $115 million US in 2007, according to the researchers.

In one study, researchers at Montreal's McGill University, King's College in London and drugmaker GlaxoSmithKline, along with colleagues in Iceland, Switzerland and the Netherlands, found that the 14 per cent of men who carry one variant on chromosome 20 and one "androgen receptor variant" showed the sevenfold increased risk.

The findings were made in a study of 1,125 Caucasian men and confirmed in an additional 1,650.

"I would presume male pattern baldness is caused by the same genetic variation in non-Caucasians," said Brent Richards, a professor in genetic epidemiology at McGill. "But we haven't studied those populations, so we can't say for certain."

The scientific discovery identified a cause of male pattern baldness, but a treatment is not imminent, the researchers cautioned.

In a second study, Axel Hillmer of the University of Bonn in Germany and his colleagues showed the frequency of the chromosome 20 variant varied worldwide.

The newly discovered gene on chromosome 20 can be inherited from both the mother and father.

"This helps to provide an explanation for the similarity [in hair growth] between father and son," said Prof. Markus Noethen of Bonn University's Institute of Human Genetics.

In 2005, scientists showed that the first known hair loss gene was inherited from mothers, which explained why hair loss in men often reflected that of maternal grandfathers.