Test offers hope on bone disease

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SCIENTISTS have invented a simple genetic test for men and women at risk of osteoporosis - brittle bone disease - which causes serious fractures in later life.

They believe the test should be able to identify about half of those who are at risk of suffering the disorder. They predict it could become available in a few years providing doctors can offer suitable prophylactic therapy to help people avoid developing brittle bones.

The test is based on research published in the journal Nature showing that a single gene plays a major role in bone growth during the first 20 years of life. Some variations in the gene put the carriers at a greater risk of osteoporosis in later life because their bones are below average density.

Bone fractures resulting from osteoporosis affect up to 60 per cent of older women, who are more liable than men to suffer rapid bone loss because of hormonal changes after the menopause. About one in every four men over 60 is nevertheless likely to suffer an osteoporotic bone fracture.

Brittle-bone disease tends to run in families, with osteoporotic women more likely to have osteoporotic daughters than non-sufferers. What has surprised bone researchers is the influence that just one gene appears to play.

''We knew it had an effect, but we didn't expect it would be of this magnitude,' said John Eisman, professor of medicine at the Garvan Institute of Medical Research in Sydney, who led the research.

Bone density varies greatly and was thought to be under the control of many different genes. The Sydney team studied sets of identical and non- identical twins to determine the role of genes and environmental influences, such as diet, on bone density. They studied the link between variations in the gene for a 'receptor' molecule which binds to the active form of vitamin D, which is known to aid the incorporation of calcium into the bone.

Variations in the gene account for up to three-quarters of the total genetic component of bone density, Professor Eisman said. Between 50 and 60 per cent of the total variation in bone density within the population result from this one gene, he added.

Greg Mundy, professor of medicine at the University of Texas Health Science Center in San Antonio, said the development of a genetic test 'gives a new lease of life to forms of vitamin D as potential treatments for osteoporosis. It gives us the ability to diagnose potential sufferers when they are very young. This is a really important find in the bone field.'