introduction
Psoriasis is a chronic inflammatory disorder of the skin, the body’s largest organ and the first line of protection from the environment. Although the cause of psoriasis is currently unknown, it seems to involve skin cells that grow abnormally fast, which causes the skin to shed every three to four days. Psoriasis is characterized by inflamed, scaly, red, itchy patches called psoriatic plaques and is a fluctuating condition with recurrent episodes of variable severity. About 10% to 20% of psoriasis patients develop psoriatic arthritis, an inflammatory joint disease. Psoriasis and psoriatic arthritis are considered to be autoimmune diseases, in which the immune system attacks the body’s own tissues.
Psoriasis is most common among people of European ancestry (with a prevalence of 2% to 3%). Women have a slightly higher risk of developing psoriasis according to some studies. Psoriasis is estimated to affect 5 to 7 million people in the US.There are three genetic variants that are known to increase the risk of developing psoriasis: HLA-C on chromosome 6, IL-12beta on chromosome 1and and IL-23R on chromosome 5. Of these three genes the HLA-C gene contributes by far the strongest effect to the risk of developing psoriasis in most if not all populations tested.
The deCODEme Genetic Scan identifies the three genetic variants listed above in customers of European descent and provides interpretation of their associated risk for the development of psoriasis. In East Asians, the deCODEme Genetic Scan currently only identifies the HLA-C variant. Currently no data are available for people of other ethnicities for the variants listed above.
risk factors
A family history of psoriasis is the greatest risk factor. In a study of identical twins, 70% of twins who had psoriasis had a twin who also had psoriasis. Studying identical twins for concordance (both twins having the same disease) is generally a good measure of genetic contribution since their inherited genetic material (DNA) is identical. A 70% concordance rate is considered to be very high for a condition of complex inheritance such as psoriasis. Psoriasis appears to involve the immune system. Therefore, it is not surprising that the gene most strongly and consistently associated with psoriasis is a gene important in immune response. HLA-C, specifically HLA-Cw6, is associated with psoriasis in most, if not all, populations tested. Commonly, over 60% of psoriasis patients carry one or more copies of the Cw6 variant of HLA-C compared with 8% to 12% of those who do not have psoriasis. On average, psoriasis patients who have the Cw6 variant tend to develop the disease a few years earlier and can have more severe progression of the disease compared with psoriasis patients who do not have the Cw6 variant. Recently, two other genes, IL-12beta and IL-23R, have been associated with psoriasis, but they do not seem to play as important a role as HLA-Cw6 in their contribution to the risk of developing the disease.more information
You can find out more information about psoriasis by talking with your doctor and visiting these Web sites: American Academy of Family PhysiciansMedlinePlus Article on Psoriasis
National Institute of Arthritis and Musculoskeletal and Skin Diseases
The National Psoriasis Foundation
Wikipedia Article on Psoriasis