LONDON (Reuters) - Researchers looking for genes that raise the risk of osteoporosis found seven different sequences associated with the bone-thinning disease, and one team found two that might predict the risk for 20 percent of people.

The studies, published in the New England Journal of Medicine and the Lancet on Tuesday, may also shed light into how osteoporosis develops.

A British team identified two small mutations called SNPs -- single-letter changes in the DNA code -- that predicted thinning bones.

They scanned the genes of 2,094 female twins and identified a link between decreased bone mineral density and changes in genes on chromosomes 8 and 11.

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One change raised the risk 30 percent and the other conferred a 20 percent higher risk.

"Eventually, a panel of genetic markers could be used in addition to environmental risk factors to identify individuals who are most at risk for osteoporotic fractures," Tim Spector and Brent Richards, researchers at King's College London wrote in their report in the Lancet.

The two genes are important target for treatments, and drugs are already under development, Spector's team said.

"These (genes) can be measured with near perfection and without bias years before the age at which fractures tend to occur -- which could provide ample lead-time for preventative measures," they wrote.

Osteoporosis affects about one in three women and one in five men globally, according to the International Osteoporosis Foundation. Up to 40 percent of women past menopause develop the disease.

Drugs called bisphosphonates can increase bone mass and cut the risk of fractures in patients with osteoporosis. Exercise, a diet rich in calcium and vitamin D and having thicker bones lowers the risk.

For the New England Journal of Medicine study, a team led by Iceland-based Decode Genetics studied 5,800 Icelanders, and compared them to about 8,000 other people in Iceland, Denmark and Australia.

Every volunteer had bone density x-rays and other tests and were asked if they had ever had a fracture.

The researchers found genetic variations in five areas that were associated with bone strength.

"Three regions are close to or within genes previously shown to be important to the biologic characteristics of bone," they wrote. They said the study provided more information on the biology underlying osteoporosis than any value to any one person.

(Reporting by Michael Kahn and Maggie Fox)