Scientists have found two new genetic variations that appear to increase the risk of the most common skin cancer among people of European descent.

The variations play no role in skin color but people with both of them are nearly three times more likely to develop basal cell carcinoma compared with people without the changes, researchers from Iceland's Decode Genetics said on Sunday.

Darker skin is traditionally regarded as an important protection against skin cancer.

"Here we have two variants that have no impact on pigmentation and only affect the risk of basal cell carcinoma," Kari Stefansson, Decode's chief executive, who led the study, said in a telephone interview. "We don't know why that is."

Basal cell carcinoma is the most common form of cancer worldwide, and in the vast majority of cases are thought to be caused by exposure to ultraviolet rays of the sun, according to the American Academy of Dermatology.

Most cases are easy to treat when detected early, but in rare instances the cancer is resistant to treatment, causing damage to skin and sometimes invading bone and cartilage.

The researchers at Decode, a biotech company hunting for new drugs using Iceland's unique gene pool dating back to the Vikings, analyzed genes of more than 30,000 people to identify the impact of the genetic variations located on chromosome 1.

These variations differed from past genetic changes linked to basal cell carcinoma in that unlike the others they were not associated with fair skin or pigmentation.

The study published in Nature Genetics also found that the risk of developing basal cell carcinoma was 12 times higher for people with these new variations along with the three other genetic changes already linked to the cancer.

"Exposure to the sun has no direct impact on the genes, which add to the total risk of basal cell carcinoma," Stefansson said.

科学家发现了两个新的基因变异似乎增加了欧洲后裔患最常见皮肤癌的风险。

来自冰岛解码基因机构的研究人员说，该基因变异对皮肤颜色并无作用，但与无基因变异的人群相比，有两种基因变异的人群患皮肤基底细胞癌的机率增加近三倍。

传统上将较黑的皮肤视为预防皮肤癌的重要屏障。

解码基因机构主任、这项研究的领导人凯里-斯蒂芬森(Kari Stefansson）在一次电话采访中说：“我们发现的这两个基因变异对色素沉着并无作用，仅仅影响患皮肤基底细胞癌的风险。对此原因，我们不知道。”

根据美国皮肤科学会（American Academy of Dermatology）的说法，皮肤基底细胞癌是世界范围内最常见的癌症，绝大部分病例被认为是由接触太阳光的紫外线引起的。

多数病例发现早时易于治疗，但极少数病例难以治疗，可引起皮肤损害，有时侵入骨头和软骨。

解码基因机构是一家利用冰岛的可追溯到维京人的基因库来搜寻新药的生物技术公司，该机构分析了3万多人的基因，以识别１号染色体上的基因变异的影响。

这些基因变异与以往的与皮肤基底细胞癌有关的基因变化不同，它们与皮肤的白与黑无关。

这篇发表在《自然遗传学》(Nature Genetics)上的论文还发现，这两个新的基因变异与另外其它三个与癌症有关的基因变化并存的人群，患皮肤基底细胞癌的风险高出常人１２倍。

斯蒂芬森说：“接触太阳光对增加皮肤基底细胞癌总风险的基因并无直接影响。”