Nature Genetics paper details the study that shows both mutations play a role in the immune system.

Researchers discovered two genes, ARTS1 and IL23R, that cause ankylosing spondylitis (AS), a chronic form of arthritis that attacks the spine and also can target other joints and organs.

“We’ve long known that the HLA-B27 gene accounts for 40 percent of the overall cause of AS,” says John D. Reveille, M.D., professor and director of the division of rheumatology and clinical immunogenetics at University of Texas Medical School at Houston. “Now we have found two new genes. Together with HLA-B27, these genes account for roughly 70 percent of the overall cause.”

Researchers from Wellcome Trust Centre for Human Genetics used genome-wide association scanning to analyze DNA samples from 1,000 patients with ankylosing spondylitis and a further 1,500 unaffected people. The researchers found that ARTS1 and IL23R increase the risk of developing the disease. The findings from this study were then confirmed by the UT Houston team.

The scientists believes that the identification of ARTS1 may explain HLA-B27’s role in AS. A protein created by the HLA-B27 gene takes fragments of pathogens and displays them on the outside of immune cells. These fragments then trigger the immune system to fight against the pathogen. ARTS1 is involved in breaking up the pathogen into bite-size chunks that can be displayed by HLA-B27.

The IL23R gene is known to play a role in the immune response to infection, providing instructions for making a receptor present on the surface of several types of immune cells. This receptor is also recognized for its part in a number of autoimmune diseases such as Crohn’s disease and psoriasis.

Investigators from the Australo-Anglo-American Spondylitis Consortium were also involved in this study. The findings are published in the October 21 online edition of Nature Genetics.

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