A new study published today in the journal Cell shows that researchers may have isolated a genetic sequence that promotes both sun sensitivity and freckles.

The study looked thousands of Icelandic citizens, comparing their DNA to determine where traits may be encoded in genes. The researchers found a specific genomic variant in the non-coding portion of a gene associated with pigmentation traits that is associated with both sun sensitivity and freckles. The same variant appears to be related to both brown hair and blue eyes as well.

“Genes involved in skin pigmentation also have important roles in human health and disease,” said Dr. Dan Kastner, NHGRI scientific director of the National Human genome Research Institute at the NIH. “This study explains a complex molecular pathway that may also contribute insights into skin diseases, such as melanoma, which is caused by the interaction of genetic susceptibility with environmental factors.”

The specific genetic variation was found in a gene known as IRF4. The sequence was found to control melanocytes – skin cells that create melanin, which colors human skin. With this specific sequence in place, melanocytes become less adept at transferring melanin to skin cells near the skin’s surface. This has the effect of leaving the upper layers of skin vulnerable to the sun’s UV rays, though people with the trait do more easily generate vitamin D3 from sunlight.

“This non-coding sequence harboring the variant displayed many hallmarks of having a function and being involved in gene regulation within melanocyte populations,” said Andy McCallion, a co-author of the study and a geneticist at Johns Hopkins University.