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In one report, a variant of the gene called STAT4 is one of the five genes now identified to increase the risk of developing rheumatoid arthritis or lupus, both of which are autoimmune disorders, where the immune system attacks healthy tissue.
STAT4 can boost a person's risk for the illnesses by 30 percent to 60 percent, depending on how many copies of the gene one has, the researchers found.
In the other study, a variant of the TRAF1-C5 gene was found to be associated with an increased risk for rheumatoid arthritis.
"There has been a huge amount of optimism about what genetics can bring," said lead researcher Dr. Peter K. Gregersen, head of the Feinstein Institute's Robert S. Boas Center for Genomics & Human Genetics in Manhasset, N.Y. "But everyone working on complex disease underestimated the size of the problem, which it is why it has taken a decade to identify genes related to these problems," he said during a Tuesday morning teleconference.
There are now five genes "that we are quite certain are involved in [rheumatoid arthritis], and I suspect there are another three to five at least that are involved," Gregersen said. "We are talking about gene variants that are fairly common in the population -- variants that are present in 5 percent or more of the population," he said.
Gregersen believes that identifying these genes will lead to new ways of predicting who is likely to develop rheumatoid arthritis. It might also lead to personalized treatments and perhaps effective prevention for those found to be at higher risk.
In the first study, Gregersen's team looked at DNA from almost 4,200 individuals with rheumatoid arthritis or lupus. Using gene mapping, the researchers identify STAT4 as a gene involved in increasing the risk for both diseases.
"Although we don't know how this gene variant changes immune function, it is clear that this finding places STAT4 pathways directly in a scheme of pathogenesis for both [rheumatoid arthritis] and lupus," Gregersen said. "This shows that a single gene can overlap autoimmune disorders."
Gregersen's group found that some 22 percent of people carry this particular form of STAT4, but that percentage rises to 27 percent in people with rheumatoid arthritis. This STAT4 variant increases the risk of developing rheumatoid arthritis by 32 percent. For people with two copies of this variant, the risk is increased by 60 percent, the researchers noted.
Patients with the STAT4 variant have about double the risk of developing lupus compared with people without the variant, the researchers reported.
In another study by Gregersen and colleagues, STAT4 was identified as an important risk gene in Koreans with rheumatoid arthritis. That paper appears in the September issue of Molecular Medicine.
Studies in mice with rheumatoid arthritis have shown that blocking STAT4 can prevent or relieve arthritis, suggesting that STAT4 could be a target for new therapies, Gregersen noted. In addition, STAT4 could help researchers identify triggers for rheumatoid arthritis, develop diagnostic tests, and to even predict who will best respond to treatments, he said.
Gregersen said his team is also looking at what role, if any, STAT4 might play in other autoimmune diseases.
In the other New England Journal of Medicine study, Gregersen's team looked at the genotype of 1,522 people with rheumatoid arthritis. They then compared these with the genotype of 1,850 people without the disease.
They found that people with the variant of TRAF1-C5 had a 32 percent increased risk for developing rheumatoid arthritis compared with people without the variant.
Dr. Daniel Kastner, of the Genetics and Genomic Branch at the U.S. National Institute of Arthritis and Musculoskeletal and Skin Diseases, was a co-author of both of the NEJM studies. He believes that the findings are groundbreaking.
"The fruits that have come forth from identifying new disease genes has had a significant impact on the care of our patients," Kastner said during the teleconference. "Although these fruits are still a way off for RA, I do have a sense of excitement that we are entering a new era with regards to our understanding of RA and some of the other autoimmune diseases," he said.
Another expert agreed.
"It is now possible to investigate disease association genes genome-wide," noted Dr. Kazuhiko Yamamoto, from the Graduate School of Medicine at the University of Tokyo, Japan, and author of an accompanying NEJM editorial.
"Genetic analyses will enhance our understanding of the disease and the development of new therapies, although more detailed, functional studies are needed," Yamamoto said. "Several associated genes will be revealed to many common diseases in the near future, but ethnic differences should be taken into consideration," he added.
SOURCES: Sept. 4, 2007, teleconference with: Peter K. Gregersen, M.D., head, Feinstein Institutes Robert S. Boas Center for Genomics & Human Genetics, Manhasset, N.Y.; Daniel Kastner M.D., Ph.D., Genetics and Genomic Branch, U.S. National Institute of Arthritis and Musculoskeletal and Skin Diseases; Kazuhiko Yamamoto, M.D., Ph.D., Graduate School of Medicine, University of Tokyo, Japan; Sept. 6, 2007, New England Journal of Medicine
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