HONG KONG, March 26 (Reuters) - Researchers in Japan have identified a gene variant that may be responsible for osteoarthritis, a painful condition in the joints that affects more than 200 million people worldwide.

Osteoarthritis usually happens in old age, when there is a breakdown and loss of cartilage in the joints, leading to swelling and pain, and restricting mobility.

The scientists said in the journal Nature Genetics they had analysed DNA from two groups of Japanese patients with hip osteoarthritis and found that the gene variant showed up more frequently in them than in a group that did not suffer from the disease.

The same variant was also found to be significantly more frequent in both Japanese and Chinese individuals suffering from osteoarthritis of the knee, they wrote.

"Association (between osteoarthritis and the variant gene) was found in Japanese populations and the association was replicated in a Chinese population," lead researcher Shiro Ikegawa at the SNP Research Center in Tokyo told Reuters.

"Those who have this susceptibility variant are 1.8 times more likely to develop osteoarthritis."

Explaining the link between the variant gene and osteoarthritis, Ikegawa said the variant probably reduces the amount of growth differentiation factor 5 (GDF5) produced.

GDF5 is a protein that is secreted by cells and is known to be involved in cartilage development, and lower levels of GDF5 may affect the maintenance of cartilage in joints.

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