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Thursday, May 10, 2012

Genetic mutation may explain mysterious blond Solomon Islanders

By Meghan Holohan

Courtesy of Sean Myles

When then-post-doctoral student Sean Myles visited the Solomon Islands, he took this photo after noticing a large number of indigenous children with naturally blond hair. A few years later this photo sparked a study that identified the genetic cause of the striking hair and skin color combination.

When Sean Myles worked as post-doctoral student in Carlos Bustamante’s lab, he showed Bustamante a photo of a Melanesian child with cocoa-colored skin and bright blond hair, wearing a U.S. military jacket.

Like others, Bustamante, a professor of genetics at Stanford University, initially believed the Melanesians’ blond hair came from Europeans who visited the islands and paired with islanders. But Myles, now an assistant professor at the Nova Scotia Agricultural College, insisted it was something different. When Myles had visited the Solomon Islands for another research project, he estimated that 5 to 10 percent of the children possessed light locks. So Bustamante and Myles designed an experiment to understand the origin of the blond Solomon Islanders. 

“I think there was some debate that the scientific community was sort of hypothesizing about,” says Eimear Kenny, a co-author and post-doctoral scholar in Bustamante’s lab at Stanford.

Bustamante, Myles, and their colleagues discovered the Melanesians’ blond hair comes from a gene mutation specific only to them. The variant is recessive, meaning that both a mother and father must carry the gene for a child to inherit flaxen hair.  

“It is interesting to have one gene that is associated with pigmentation in a tropical population with blond hair,” says Rasmus Nielsen, professor of integrative biology at the University of California, Berkley, who is not part of this study. “There are lots of different mutations that impact skin and hair color and in this case there is one mutation that impacts it, which is quite unusual.”

In 2009, Myles collected 1,000 samples by traveling from village to village on the Solomon Islands, working with local chiefs for permission. The researchers first tested 100 samples to look for genetic mutations and were shocked to find one gene contributed to the blond hair—and this gene differed from what caused blondness in Northern Europeans and their descendants.

The test of the remaining 1,000 samples yielded the same results. The researchers noticed a signal on chromosome 9 and when they dug deeper, they discovered that TYRP1, known for influencing pigmentation in mice and humans, caused the blond hair.

“Pretty much everything about these results was surprising. This is really not what we were expecting,” says Kenny. “We did not expect to find a single gene.”

Generally, a number of genes contribute to skin or hair color, for example. There could be anywhere from 10 to hundreds of genes impacting whether a person is blond. 

While this discovery might appear to answer a simple question, the results have larger implications. Most genetic studies look at North Americans or Europeans and researchers translate the results to represent all people.

“[This impacts] how we think about the design of medical genetic studies and the importance of broadening representations in medical studies,” Bustamante says.

And Nielson believes that researchers will gain a better understanding of the human genome by rethinking experiments. 

“You can look at small isolated populations and find very interesting genetic variants,” Nielson says.

The study was published Friday in Science.

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