PARIS, Feb 24, 2008 (AFP) - Researchers have found the genetic basis of two distinct forms of inherited hair loss, opening a broad path to treatments for thinning locks, according to a pair of studies released Sunday February 24th.

Creeping baldness is a source of distress to tens of millions the world over.

Hair-challenged adults spend upward of a billion dollars every year on mostly bogus remedies in the United States alone, according to the Federal Drug Administration.

They also lavish at least as much on sometimes painful hair implants and other forms of more or less convincing hair substitutes.

Geneticist Regina Betz of the University of Bonn and her colleagues hunted down a gene -- P2RY5 -- that causes a rare, inherited form of hair loss called Hypotrichosis simplex.

They found their quarry, after six years of research, among families in Saudi Arabia.

It is the first receptor in humans known to play a role in hair growth, according to the study, published in Nature Genetics.

"Although Hypotrichosis simplex is very uncommon, it may prove critical in our search for an understanding of the mechanisms of hair growth," said Betz.

The disease affects both men and women, who begin to go bald during childhood.

At fault is a genetic defect that prevents certain receptors on the surface of hair follicle cells from being correctly formed.

For the hair follicle to function normally, messengers must bind to these receptors, triggering a chain reaction in the cell interior.

The fact that a receptor plays a specific role in hair growth was previously unknown to scientists.

"We can now search selectively for related substances that may be used in therapies for very different types of hair loss," said Ivar von Kügelgen of from Bonn's Institute of Pharmacology and Toxicology.

In the other study, Angela Christiano of Columbia University lead a team that found another mutation of the same gene that results in "woolly hair" -- sparse, dry and tightly curled hair over the entire scalp.

Examining families in Pakistan, the researchers determined that the mutation is expressed in the inner root sheath of hair follicles, which anchor and shape individual hairs.

Until recently, many scientists assumed that mammalian hair follicles were a non-renewable resource.

The human head comes equipped with approximately 100,000 of these tiny, hair-generating organs, and once they stop working, it was thought, the scalp was doomed to gradual exposure.

A healthy individual loses around a hundred hairs a day, but they are normally replaced at the same rate.