Researchers uncover new genetic links to psoriasis

Bowcock and her team found seven novel DNA variations linked to psoriasis. Four other variations associated with the disease that had been identified previously by other researchers also were confirmed by the current study.

Whole genome association studies have recently been used to identify common genetic variations that increase the risk of diseases such as breast cancer, heart disease and type 2 diabetes. They typically involve more than 1,000 patients with a particular disease to help ensure that the genetic variations identified in the study do not occur by chance. While the current study included fewer patients, nearly half of them had a sibling and, in some cases, a parent with psoriasis, which increases the odds of finding genetic variations that contribute to the disease.

The researchers found the strongest genetic risk for psoriasis lies in a region of the genome that contains the major histocompatibility complex, a collection of genes involved in distinguishing the body's own cells from foreign invaders. "Although this region has been known to play a major role in psoriasis, DNA variations in the MHC alone have been known to not be enough to trigger disease," Bowcock says. "Only 10 percent of patients with variations in the major histocompatibility complex developed psoriasis. This tells us that other genetic or environmental factors also contribute to the disease."

One MHC variation linked to psoriasis and psoriatic arthritis occurs in the gene HCP5, the scientists noted. That variation was recently reported to delay the onset of AIDS in people infected with HIV. This is particularly interesting, Bowcock says, because psoriasis can be triggered by infection with HIV or other viruses. It may be that in people with this SNP variant, viral infection triggers a larger immune response that slows the development of AIDS but also leads to excessive inflammation in the skin and bone joints in genetically susceptible individuals, leading to the onset of psoriasis and psoriatic arthritis.

Notably, DNA variations on chromosome 4 were strongly linked to psoriatic arthritis. These same variations were also associated with psoriasis and had been previously linked to type 1 diabetes, rheumatoid arthritis, Grave's disease (caused by an overproductive thyroid gland) and celiac disease (caused by the inability to digest gluten). "Doctors have noticed that some psoriasis patients have autoimmune diseases such as celiac disease, Grave's disease, and type 1 diabetes," Bowcock says. "But we didn't know whether this was a coincidence. Now we know there is a genetic component underlying all of these diseases."