
                         Roanoke Times
                 Copyright (c) 1995, Landmark Communications, Inc.

DATE: THURSDAY, January 20, 1994                   TAG: 9401200035
SECTION: NATIONAL/INTERNATIONAL                    PAGE: A-6   EDITION: METRO 
SOURCE: Associated Press
DATELINE: NEW YORK                                LENGTH: Medium

GENE THAT MAY CAUSE OSTEOPOROSIS LOCATED

Scientists have found that a single gene may influence the risk of osteoporosis, suggesting a way to identify people vulnerable to the bone-weakening disease while they're young enough to take preventive steps.

The disease, which affects 25 million Americans and causes about 1.5 million fractures a year, has no early symptoms and usually is not diagnosed until after age 50 when a fracture occurs.

But if the finding by Australian researchers is confirmed, a test to assess the gene may one day identify vulnerable people in childhood, when such precautions as taking extra calcium might fortify their bones enough to avoid later fractures, specialists say.

"I think it's one of the most exciting discoveries in osteoporosis research in the last decade," said Dr. B. Lawrence Riggs, professor of medicine at the Mayo Clinic and Foundation in Rochester, Minn. He cited the prospects for a test and the clues the finding gives for developing bone-building treatments.

In osteoporosis, bones deteriorate from excessive loss of tissue. Fractures typically occur in the hip, spine or wrist, but can appear in other bones. Women are more susceptible than men.

The research is reported in today's issue of the journal Nature by Dr. John Eisman and colleagues of the Garvan Institute of Medical Research at St. Vincent's Hospital in Sydney.

They found that the gene has a major effect on bone density, which previously has been shown to predict fracture risk.

The gene tells the body how to make the receptor, or protein structure, that vitamin D uses to exert its effects. Different versions of the gene were associated with different average bone densities.

The vitamin D receptor plays a role in the body's absorption of calcium from food and in other processes involving calcium, Eisman said. But it is not known why different gene versions affect bone density, he said.

Eisman said he believed that question could be answered in a year or so. Knowing that, scientists might be able to tailor preventive treatment to people based on whatever versions of the receptor gene they have, he said. One person might respond best to calcium, and another to doses of the hormonal form of vitamin D, he said.

The receptor gene comes in two versions, dubbed "b" and "B." The research linked the "b" version to higher bone density at two common fracture sites, the top of the thigh bone and in spinal bone.

People inherit one version of this gene from each parent, and their combined inheritance can be described as bb, Bb or BB. In 21 of 22 healthy Caucasian twin pairs who differed in their inheritance, researchers found spinal bone densities were higher in the twin with more "b" versions.

In a group of 311 healthy unrelated women, researchers found the genetic inheritance was related to how early a woman's density declines to the "fracture threshold," the level at which the fracture risk starts to increase.

Eisman said studies in Australia, Minnesota, San Francisco and Britain suggest that about one-seventh of the population is BB, about half is Bb and about one-third is bb.

by CNB