NEW ORLEANS (Reuters Health) - A study in identical twins has uncovered a previously unknown gene with strong associations to both multiple sclerosis (MS) and rheumatoid arthritis, researchers report.

The finding is "just one more piece of the puzzle" in the search to find the causes--and, it is hoped--cures for these two common, debilitating diseases, said graduate student researcher Carolyn Greene of Georgetown University in Washington, DC. She and her colleagues presented the findings here Wednesday at the annual Experimental Biology 2002 meeting.

MS and rheumatoid arthritis are both autoimmune disorders, illnesses where the body's immune system inexplicably attacks healthy tissue. In MS, immune cells gradually wear away the protective myelin sheath surrounding nerve fibers in the brain and spine, leading to increasing neurological and motor impairment. In rheumatoid arthritis, tissues lining the joints become the focus of attack, causing patients pain and disability.

Seeking to find genes linked to MS, Greene and her co-researchers conducted detailed comparisons of the genetic make-up of a set of identical twins, only one of whom suffered from MS. Just such a gene turned up, and was active at a rate 8.5-times higher in the MS-affected twin compared with the healthy twin. Greene said the gene appears to have been previously unknown, since it "didn't match to anything" in GenBank, the human genome database.

To rule out the possibility that the finding was a fluke, the researchers then looked for the gene in a group of healthy individuals and another group of 13 MS patients. As expected, only the MS group had high levels of gene activity.

The Georgetown researchers also tested individuals with other forms of autoimmune disease for high levels of gene activity. Five patients with rheumatoid arthritis tested all had high levels, Greene said. On the other hand, patients with another autoimmune condition, Crohn's disease, displayed normal levels of the gene.

Greene stressed that both MS and rheumatoid arthritis are complex diseases likely to have both genetic and environmental causes. This discovery, she said, was just one step on a much longer journey. The next step is to try and determine what role the gene might play in triggering either disease.

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