BOSTON - Two genetic mutations raise the risk of rheumatoid arthritis, one by as much as 87 percent, researchers reported on Wednesday in a discovery that sheds more light on a complex and baffling disease.

They said their findings also show a link between rheumatoid arthritis and other diseases caused when the immune system mistakenly attack healthy tissue, such as lupus.

People who had two copies of one gene, found in a region known as STAT4, had a 60 percent higher risk of rheumatoid arthritis, the international team of researchers reported in New England Journal of Medicine.

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