March 17, 2006 -- A common genetic variation in an immune system gene may help explain why some people are more likely to develop psoriasis than others.
Psoriasis is a common and chronic disease that causes patches of itchy, scaly, and often inflamed skin. The symptoms can vary from mildly irritating to potentially disfiguring and affect about 2% of Americans. Psoriasis can also develop into psoriatic arthritis, which can be painful and debilitating.
Drugs used to treat psoriasis target the irregular immune system response that is thought to trigger the disease. These drugs counter this immune response but can leave the body more susceptible to infection.
By finding the specific gene that triggers the disease, researchers say more targeted psoriasis treatments could be developed.
"What we're all shooting for is trying to find out which branches of the immune system are triggering psoriasis, so you don't have to shut down the whole immune system -- only the parts that are important," says researcher James T. Elder, MD, PhD, professor of dermatology and radiation oncology at the University of Michigan Medical School, in a news release.
Psoriasis Gene Found
In the study, published in the American Journal of Human Genetics, researchers isolated the gene PSORS1 (for psoriasis susceptibility 1) as a major player in psoriasis susceptibility from among a field of several genes that regulate how the immune system fights off infection.
Researchers say the gene's role in triggering psoriasis was demonstrated in 2,723 people from 678 families in which at least one family member had the skin disease.
But having the gene isn't enough to cause the disease.
"For every individual with psoriasis who carries the PSORS1 gene, there are 10 other people with the gene who don't get psoriasis," says Elder.
"It's as if you are pushing a shopping cart down the aisle at the grocery store and putting genes in your cart," Elder explains. "There are several different brands of each gene on the shelf and one of them is bad for you. If you pull down enough bad ones, then you can get sick.
"But even if you get all the bad genes, you still need a trigger from the environment to develop the disease," says Elder. In some cases, that trigger may be infection, such as strep throat.
Researchers say the next step is to identify the other inherited genes that may play a role in psoriasis in order to develop better treatments for the skin disease.