April 11 (HealthDay News) -- Researchers have discovered seven common DNA variations that increase the risk of a person developing psoriasis, one of which links the skin condition and psoriatic arthritis to other autoimmune disorders.

The findings, published April 4 in the open-access journal PLoS Genetics, may help define some of biological pathways that cause psoriasis and aid in the development of treatments that target these specific avenues.

"Common diseases like psoriasis are incredibly complex at the genetic level," lead investigator Anne Bowcock, a professor of genetics at the Washington University School of Medicine in St. Louis, said in a prepared statement. "Our research shows that small but common DNA differences are important in the development of psoriasis. Although each variation makes only a small contribution to the disease, patients usually have a number of different genetic variations that increases their risk of psoriasis and psoriatic arthritis."

Psoriasis, in which the body's immune cells mistakenly attack the skin, is characterized by red, scaly patches that can be itchy, painful or both. The autoimmune disease affects an estimated 7 million Americans. Up to 30 percent of sufferers may also develop psoriatic arthritis, an often excruciatingly painful and debilitating condition.

For the study, the researchers looked at common variations in the DNA genome called single nucleotide polymorphisms (SNPs). About 10 million SNPs affect the genome to make each individual unique. Some SNPs also affects a person's predisposition to disease or good health.

The investigators scanned more than 300,000 SNPs in the genomes of 223 psoriasis patients, including 91 who had psoriatic arthritis, and compared them to those found in 519 healthy control patients.

Researchers found seven unique DNA variations linked to psoriasis. Several found 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 overactive thyroid gland) and celiac disease (caused by the inability to digest gluten).

A larger genome-wide association study of psoriasis patients is under way, and Bowcock said she expects it to find more genetic variations linked to the condition.

SOURCE: Public Library of Science, news release, April 3, 2008