e 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," explains Elder. "In psoriasis, strep throat is a very common initial trigger. It activates the immune system to attack the strep bacteria. But once the strep infection is cleared, the immune system starts attacking the patient's own skin cells.
About half the time, strep-induced psoriasis goes away and never comes back. But for the other 50 percent of young people who get it, psoriasis progresses to become a chronic life-long disease."
The PSORS1 gene is actually one of over 20 different varieties (scientists call them alleles) of a gene called HLA-C. "In terms of our grocery store analogy, think of PSORS1 as one of 20 'brands' of HLA-C on the shelf," Elder says.
Located on human chromosome 6, HLA-C is one of several genes in the major histocompatibility complex (MHC) that regulate how the immune system fights off infection. MHC genes carry DNA-coded instructions for proteins whose job it is to distinguish between what belongs in the body and what doesn't.
"There is a great deal of genetic variation in the MHC, because it's on the front lines of dealing with pathogens and cancer," Elder explains. "It's an area where it's good to be different. If everybody were the same, we'd be like hybrid corn. A plague could come along and wipe us all out."
Scientists have been searching for genes associated with psoriasis for more than 30 years, but until now studies have been inconclusive, according to Rajan P. Nair, Ph.D., the study's first author and a U-M assistant research professor in dermatology.
"Researchers have identified 19 candidate loci, or areas on chromosomes, that may be genetically linked to psoriasis," Nair says. "Many studies confirmed a strong association with the MHC, but no one could determ
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Source:University of Michigan Health System
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