(LifeWire) - Some genetic associations seem simple: You got Dad's eyes, Mom's nose and Aunt Ida's goofy smile. But to whom can psoriasis patients trace their problematic skin? That's a puzzle scientists are working hard to solve.
To date, researchers have uncovered nearly a dozen variations in the DNA, or genetic material, of people with psoriasis -- an autoimmune disorder that produces thickened patches of scaly, red skin that can appear on any part of the body. While the disorder's onset usually occurs between the ages of 15 and 35, psoriasis can strike at any age and affects men and women equally. The disease has no known cause or cure.
While the genetic links to blue eyes or brown hair are well understood, scientists remain stumped on the genetics of psoriasis. In part, that's because psoriasis appears to develop from a baffling interplay between genetics and environmental triggers. Despite the steady gains in information - fueled by a vocal group of roughly 6 million patients in the United States alone - there is still much to be discovered.
"Genetics certainly increase your susceptibility, but they don't guarantee that you'll get it," says Doris J. Day, MD, assistant clinical professor of dermatology at New York University Medical Center.
In fact, an April 2008 study in the journal Public Library of Science Genetics found that only 10% of study participants who had gene variations common to psoriasis actually developed the disease. For this research, scientists at the Washington University School of Medicine in St. Louis examined the genes of 223 psoriasis patients, including 91 who had psoriatic arthritis, and compared their DNA variations with 519 healthy patients.
Notably, the researchers also found that one set of gene variations common to those with psoriasis and psoriatic arthritis are linked to those of four other autoimmune disorders -- type 1 diabetes, celiac disease, Grave's disease and rheumatoid arthritis -- demonstrating that certain autoimmune disorders may have similar genetic pathways.
Possible Genetic Links Between Psoriasis and Psoriatic Arthritis
There is much stronger scientific evidence of a genetic link between psoriasis and a related joint condition known as psoriatic arthritis, which affects 10 to 30% of those with the skin disorder. In fact, according to a 2005 study in Annals of the Rheumatic Diseases, the incidence of psoriasis is an astounding 19 times higher among first-degree relatives (parents and siblings) with psoriatic arthritis than it is among the general population.
Perhaps the golden question, though, is whether psoriatics or healthy people who have a family history of the disease can prevent passing it on to their children. The answer, according to Day, is a firm, "No, absolutely not."
Still, Day adds, there's no guarantee that children of psoriatics will inherit the disorder. Patients can also find hope in researchers' ongoing quest to learn more about psoriasis, since each piece of knowledge will contribute to more targeted therapies.
Day, Doris J., MD, assistant clinical professor of dermatology, New York University Medical School. Telephone interview. 16 May 2008.
Liu, Y., et. al. "A Genome-Wide Association Study of Psoriasis and Psoriatic Arthritis Identifies New Disease Loci ." Public Library of Science Genetics 4:3 (2008). <http://www.plosgenetics.org/doi/pgen.1000041>
Rahman, P., and J.T. Elder. "Genetic Epidemiology of Psoriasis and Psoriatic Arthritis." Annals of the Rheumatic Diseases 64:2. (2005) 37-39. <http://ard.bmj.com/cgi/content/abstract/64/suppl_2/ii37>
"The Role of Genetics in Psoriasis." Psoriasis.org. Oct 2007. National Psoriasis Foundation. Accessed 3 Jun 2008. <http://www.psoriasis.org/research/known/genetics.php>