People with the skin pigmentation disorder vitiligo may have less risk of developing life-threatening malignant melanoma, according to new research. The study also further confirms the suspicion that vitiligo is an autoimmune disease, which occur when the body's immune system reacts against its own tissues or organs. This could lead to new treatments for vitiligo.

Vitiligo is a chronic condition that affects one in every 200 people. The study - published online today by the New England Journal of Medicine - argues against the theory that the pale skin patches caused by vitiligo increase the risk of melanoma due to their lack of the pigment melanin. Melanin gives skin its colour, and protects against harmful UV rays from the sun.

While vitiligo is thought to be partly triggered by environmental and lifestyle factors, the cause is also known to have a genetic element. The St George's, University of London team and colleagues from the University of Colorado School of Medicine have discovered that a common variant in the gene tyrosinase (TYR) increases vitiligo susceptibility. This variant was already known to give decreased susceptibility to melanoma.

Professor Dot Bennett, who led the St George's team, said: "Although this may provide some consolation for people with vitiligo, they should still be careful in the sun. As they know, they sunburn quickly, and a lower risk of cancer doesn't mean zero."

Seventy per cent of the population have the variant that increases the chance of vitiligo and reduces the risk of melanoma. The remaining 30 per cent have another variant that increases the risk of melanoma but decreases the chances of vitiligo. Although everyone has one of the two variants, neither guarantees vitiligo or melanoma will actually develop. Likewise, neither guarantees protection, and there are genes other than TYR that can trigger both melanoma and vitiligo.

The findings came from a genome-wide association study - an examination of variation across the complete genetic make up - of 1,514 with vitiligo, with a control group of 2,813 people without the disorder. Researchers tested 579,146 single-nucleotide polymorphisms - tiny variants in the DNA sequence - for any association with vitiligo.

Prof Bennett added that the study further confirmed the belief that vitiligo is an autoimmune disease. The researchers linked seven genes to vitiligo that were already associated with autoimmune disorders such as childhood diabetes, rheumatoid arthritis and lupus. Two other genes were identified that are associated with vitiligo and with the immune system, although not related to any other disease.

Prof Bennett added: "Another reason the findings are important is that there are still some vitiligo researchers who are not convinced about the importance of the immune system. As nine out of ten of the genes newly found to be associated with vitiligo are connected with the immune system, it really begins to be impossible not to believe that immunity is important in this disorder.

"This gives new support to an old idea, that our immune system may help us not to get cancer, by killing potential cancer cells before they get started.

"This also underlines the idea that successful treatment is likely to include an element of calming down the immune response. My prediction is that combining this with something to make the remaining pigment cells divide faster, to fill in the white patches, is what will work best."

Source: St George's, University of London

http://content.nejm.org/cgi/content/full/NEJMoa0908547