Scientists have discovered a gene needed to start puberty, zeroing in on it by studying families in which cousins had married each other.

The find could lead to more effective treatments for youngsters who fail to mature sexually, and could shed light on the causes of other reproductive disorders, researchers said.

Three sets of researchers in the United States, France and England identified the gene simultaneously.

The gene is not on the X or Y sex chromosome. Instead, it is on one of the ordinary paired sets of chromosomes, No. 19. That means one good copy is enough to start puberty. But two defective copies - one from each parent - can keep the body from maturing, a condition that usually can be treated with hormones.

"The discovery is an important step in understanding the elaborate sequence of events needed for normal sexual maturation," said Dr. Duane Alexander, director of the National Institute of Child Health and Human Development, which helped pay for the studies.

Teams of researchers from Boston and from Cambridge, England, reported their findings in Thursday's New England Journal of Medicine. A group from Paris published its own findings in last week's Proceedings of the National Academy of Sciences, which first posted them online on Aug. 27.

The researchers said the gene may affect the production or processing of a particular sex hormone.

However, this one gene does not provide all the answers to why some youngsters do not go through puberty normally. Other genes are known to cause this condition, called idiopathic hypogonadotropic hypogonadism, and scientists do not think they have found all of its causes.

Environmental factors, such as nutrition, exposure to various chemicals, and even exercise also play a role in the onset of puberty.

The gene discovery might lead to better treatment for spreading prostate cancer and other ailments, scientists from Harvard Medical School and an affiliated hospital wrote in an accompanying article.

The U.S. team, at Harvard and two affiliated hospitals, worked with a Kuwait University researcher to identify the gene by studying a Saudi Arabian family in which six adults were infertile even after hormone treatment. The six were among 19 children from three sets of married cousins.

Two other genes known to be involved in the same disorder are on the X chromosome, but because of the way the disease ran in the Saudi family, researchers expected to find this gene on one of an ordinary chromosome.

The French team looked at a family in which five of eight children had the disorder. The one who first came for treatment was 20 years old but only 4-foot-9, and had undeveloped genitals.

Researchers at the University of Cambridge and Paradigm Therapeutics Ltd. in Britain confirmed the U.S. team's discovery by creating mice without the gene, called GPR54. Mice lacking the gene never reached adolescence.

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Last updated: 10/23/2003 - 12:43 PM