The Role of Family History
Several specific genes, which can be passed down from generation to generation, have been identified as playing a large role in the complicated process that leads to psoriasis and psoriatic arthritis. Scientists believe that at least 10 percent of the general population inherits one or more of these genes, however, only a small percentage of those people develop either disease. Only two percent to three percent of people encounter the "right" mix of genetics and environmental triggers that lead to the development of psoriasis and/or psoriatic arthritis. Those who have a genetic disease but do not have a family history of the disease may have inherited two genes from their father and two from their mother. However, if all four genes weren’t inherited, the disease may never develop in the patient.
Research suggests that as many as 40 percent of people with psoriatic arthritis have a history of psoriasis or psoriatic arthritis in their family and the closer the relative, the higher the risk of disease. For example, the closest relatives of patients with psoriasis or psoriatic arthritis have a 50-fold increased risk of developing the disease. In identical twins, there is a 75 percent chance that the other twin will have psoriatic arthritis. That risk drops to about one third for fraternal twins and even lower, to approximately 8 percent, for siblings.
As researchers delved further into the genetic patterns that develop among families with these diseases, they learned that patients whose fathers have psoriatic arthritis are twice as likely to get the condition as they would be if their mothers were affected.
