Affecting men and women equally, about 10% to 30% of people with psoriasis develop psoriatic arthritis. Psoriatic arthritis may develop at any age, but usually affects people between the ages of 30 and 50. While the cause is not known, genetic factors, along with the immune system, likely play a role in determining who will develop the disorder.
As many as 40% of people with psoriatic arthritis have a family history of skin or joint disease. Having a parent with psoriasis triples the chance of getting psoriasis yourself and thus increases the chance of developing psoriatic arthritis.