Will I give it to my children, or will I get it if a relative has the disease?
Psoriasis is thought to be caused by a combination of genetics and environment. Although several genes have been associated with an increased risk of psoriasis, the significance of any one gene in the development of psoriasis is not known.
Several genes are more common in psoriasis sufferers and less common in the general population. Although the genes have many different functions, most are part of the immune system. The most important ones are part of the HLA, or human leukocyte antigen (HLA) sys-tem.
The HLA is a group of genes on chromosome 6 that encodes sequences, or directions, for proteins on white blood cells. The white blood cells, primed to defend against infection, are sometimes activated inappropriately. In psoriasis and other immune-mediated diseases, the immune system, led by the white blood cells, is inappropriately activated in different parts of the body. In psoriasis, these white cells, including a subset called T cells, become activated in areas of skin. These areas of skin respond with the skin thickening, redness, and the scale of psoriasis.
Efforts to scan the entire genome of psoriasis patients have confirmed that there are multiple common genes associated with psoriasis. These reports continue to show that HLA-C is of substantial importance and also implicate genes related to interleukin 12, interleukin 23, and tumor necrosis factor (TNF). These discoveries are consistent with our knowledge about how some of the newer biologic therapies are known to work. (See Questions 65 and 66.) Affected people may have a combination of several relevant genetic variants that predisposes them to the disease.
At this time, the interaction between these genes, the T cells that carry them, and changes in the skin are still being explored. The knowledge we have, however, pro-vides hope that there may be improved therapy in the future based on a person’s genetics. These results are still preliminary and currently cannot be used to determine the risk of psoriasis, disease prognosis, or therapy. No genetic tests are available or required to treat psoriasis.
Although psoriasis has a genetic component, it is not a predictably inherited disease. When a person has psoriasis, the chance of his or her child acquiring the dis-ease is less than 20%. There is no blood test, genetic test, or prenatal diagnostic that currently predicts whether a baby will have psoriasis in the future. This means that when one family member has psoriasis, the risk is increased for the other family members but can-not be predicted for a specific person.
Studies have guided our understanding of genetics in psoriasis, but can be limited by the availability of information on family members. For example, psoriasis might be described by some as “bad dandruff ” or eczema, depending on how it appears. As a result, the exact chance of a person getting psoriasis can be hard to predict.