Genetic clues to psoriasis revealed

European researchers have identified for the first time a number of genetic variants indicating increased risk of the skin disease psoriasis.

They are reported in five papers published this week in Nature Genetics.

One of the papers comes from the Wellcome Trust Case Control Consortium 2 (WTCCC2), and reports for the first time the interactions of two specific genetic regions in humans, previously not known to interact.

The WTCCC2 is a series of genome-wide association studies looking into 13 different conditions including ankylosing spondylitis, glaucoma, ischaemic stroke, multiple sclerosis and Parkinson's disease.

Psoriasis is an autoimmune disease which occurs when the body's immune system wrongly transmits signals causing skin cells to divide too quickly, often causing itchy, sometimes painful patches to appear on the skin. Between two and three percent of Europeans have psoriasis with between 10 and 20 percent of these people developing psoriatic arthritis, an incurable inflammatory joint disease.

In searching for small DNA variations that could be important in the development of psoriasis, an international team of scientists from the Genetic Analysis of Psoriasis Consortium and the WTCCC2 carried out a genome-wide association (GWA) study of 2622 patients with psoriasis and 5667 healthy subjects from the UK.

What they found were eight regions of the human genome until now not thought to be linked with psoriasis. Further, seven of the regions were identified as harbouring genes with recognised immune functions. Six of the loci were confirmed in a European study of over 9000 people; the remaining two had a weaker association.

The study also found strong evidence of interactions between the HLA-C and ERAP1 regions of DNA.

Genuine genetic interactions occur when two independent regions of DNA known to be key to a disease work together and significantly increase the risks of it occurring. The researchers said that this is possibly the first time that such an interaction has been identified in humans.

In a second study, which also used data generated by the WTCCC, an international team of scientists led by Professor André Reis from the University of Erlangen-Nuremberg, Germany, found that the gene TRAF3IP2 increased susceptibility to both psoriasis and psoriatic arthritis. Their GWA study looked at 609 German individuals with psoriatic arthritis and 990 healthy individuals.

"We need to understand why psoriasis occurs and why individuals are more likely to develop the condition," said Professor Richard Trembath from King's College London, co-leader of the first study.

"Through our research, and other studies now coming through, the research community have identified genes that play a role in people's susceptibility to the condition.”

"This work provides evidence of possible targets for future treatment strategies and this information is an important basis for further studies."