RA runs in families. If you have a close relative with the disease, your chances of having it are higher. Women are more likely than men to get RA. Usually the symptoms start between ages 40 and 60.
PsA also runs in families. Certain genes may be linked to the condition. Compared to RA, PsA often starts at a younger age, between 30 and 50.
Researchers don't know exactly what triggers either type of arthritis. But they think it probably comes from a mix of genes and other factors, including hormones and bacterial or viral infections that may send the immune system into overdrive.