A new study has found two genetic variations that play a causative role in the bone disorder osteoporosis.
Single flaws in the two genes, located on Chromosome 8 and Chromosome 11 respectively, are linked to loss of bone density in the lumbar spine and in the femoral neck, as the ball-and-socket joint of the hip is known.
The evidence comes from a genome study of 2,094 female twins, whose results were then compared to the profile of 6,462 other people in Western Europe.
When functioning properly, the two genes control proteins that are essential for maintaining bone density.
The culprit variants were found in a fifth of the population studied, and their presence boosts the probability of osteoporosis by between 20 and 30 percent.
Identifying them should open the way to new diagnostic tests to help women at risk, say the authors, led by Tim Spector and Brent Richards of King's College London.
Osteoporosis costs 17 billion dollars (nearly 11 billion euros) a year in direct medical expenses, according to figures cited in the paper, published online by The Lancet.