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Psoriatic arthritis mutilans (PAM) is a rare and very serious form of joint disease in psoriasis characterized by the breakdown of bone tissue and joint structures in small joints of fingers and toes. Despite its severity, no genetic risk factors for PAM have been identified before.

The PAM study was initiated more than 10 years ago by Mona Ståhle, KI, as a collaboration between dermatologists and rheumatologists in the Nordic countries. The clinical and epidemiological background has been described in several publications such as Disease activity and quality of life of patients with psoriatic arthritis mutilans; .

In the new study, researchers analyzed the genome of 61 patients with PAM in the Nordic countries. They found that four of the patients had rare gene variants of NADPH oxidase 4 (NOX4), an enzyme that produces oxygen radicals in the body. Oxygen radicals are reactive molecules that can cause damage to cells and tissues. NOX4 is also involved in the formation of so-called osteoclasts, cells that break down bone tissue.

The researchers’ hypothesis is that the identified NOX4 variants in people with PAM lead to increased production of oxygen radicals, which in turn results in increased breakdown of bone tissue and joints.

“The study is the first to link high levels of oxygen radicals to the development of PAM and gives hope for new treatment options for these severely ill patients”, says Isabel Tapia-Paez, researcher at the Department of Medicine, Solna, Karolinska Institutet, who led the study.

The research was funded by the Swedish dermatology foundation, Swedish Rheumatism Association, King Gustav V’s 80th Anniversary Foundation, Swedish Psoriasis foundation and the European Academy of Dermatology and Venereology (EADV).

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