What causes psoriatic arthritis?
The main contributing factors to the development of psoriatic arthritis are genetics, immunological factors and the environment.
- Genetics
- As in psoriasis of the skin, many patients with psoriatic arthritis may have a familial tendency toward the condition. However, a twin study found that arthritis was as common in dizygotic (fraternal) twins as in monzygotic (identical) twins so unknown environmental factors may also be important. First-degree relatives of patients with psoriatic arthritis have a 50-fold increased risk of developing psoriatic arthritis compared with the general population. It is unclear whether this is due to a genetic basis of psoriasis alone, or whether there is a special genetic predisposition to arthritis as well.
- Immune factors
- There is evidence to support the theory that psoriatic arthritis occurs as a result of an abnormal interaction between the immune system and the joints. People with psoriatic arthritis seem to have an overactive immune system as is evidenced by raised inflammatory markers, in particular tumour necrosis factor (TNF), and increased antibodies and T-lymphocytes (infection-fighting cells).
- Environment
- Presumably some environmental factor tips the balance in favour of the development of psoriatic arthritis in an individual who is genetically predisposed to the condition. As yet no reliable environmental factor has been identified.
