deCODE genetics announced that team of deCODE scientists has mapped to a small segment of chromosome 16 a gene contributing to psoriatic arthritis. This represents the first genetic factor outside the major histocompatibility complex (MHC) region on chromosome 6 with significant linkage to any psoriasis-related phenotype.

"Our breakthrough findings in psoriasis underscore the unique power of our population approach for tackling the genetics of just about any common condition, and we hope to push this program forward to identify the gene involved as well as targets for the development of new therapies," said Dr. Kari Stefansson, CEO of deCODE genetics.

Psoriatic arthritis (PsA) is a condition that affects approximately 10% of those who suffer from psoriasis. Like other forms of arthritis, it involves swelling and deterioration of the cartilage in the joints, causing stiffness, pain and disability. Current therapies are focused principally on symptomatic relief, due in part to a lack of understanding of the basic biology of the disease. deCODE's genetic research is aimed at identifying the genetic factors involved, as a means of identifying new drug and diagnostic targets that can target the underlying cause of disease and point the way towards more effective treatment and revention strategies.

To map the gene, the deCODE scientists and collaborating doctors from the National University Hospital in Reykjavik identified 178 patients diagnosed with PsA from the nearly 1000 patients participating in the company's program in psoriasis. Using deCODE's national genealogy database, 100 of these patients were found to fall into 39 families, and a genome-wide scan was conducted with 1000 microsatellite markers. A suggestive locus on chromosome 16 was then genotyped with a denser marker set, yielding a LOD score of 2.17 for the group as a whole, but a LOD score of 4.19 for those related through their paternal lineage. This is far above the standard criteria for genome-wide signficance, and represents the first such genetic factor outside the MHC ever mapped in a psoriatic condition. This locus also overlaps with a significant locus deCODE has identified in osteoarthritis, suggesting that the gene in question may influence the susceptibility of the joints in general, interacting with other genetic or environmental factors that determine the particular type of arthritis that develops. This is a particularly exciting prospect, as it could point the way towards drug targets and the development of broadly applicable new therapeutics that could work to counteract inherited weaknesses in the joints.