Adaptive No More

A benefit in prehistoric lean times, genetic variant may increase risk of gestational diabetes.

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By Tina Hesman Saey, Science News

A genetic variation that may increase a woman’s risk of gestational diabetes is widespread today because it was actually beneficial to early agricultural populations, a new study suggests.

Pregnant women who carry two copies of a low-activity form of the gene GIP have higher blood-glucose levels—a marker of gestational diabetes risk—Sheau Yu Teddy Hsu of Stanford University and colleagues report online February 7 in Diabetes. But when the gene’s low-activity version arose somewhere in Eurasia an estimated 8,100 years ago, that same glucose-boosting quality may have helped women maintain their pregnancies during lean times.

The new work takes an important step toward characterizing how one particular form of a gene shapes physiology and how evolution may act on that gene, says Joshua Akey, an evolutionary biologist and population geneticist at the University of Washington in Seattle.

Hsu and his colleagues recently reported evidence that the low-activity version of the GIP gene first appeared about 8,100 years ago and rapidly became part of the genetic makeup of Eurasians. Today about half of Europeans carry the new form of GIP, while 70 percent or more of Asians do. Only about 5 to 10 percent of Africans have the new form of the gene.

“It arose very fast, so it must have some dramatic effect on human viability,” Hsu says.

GIP helps stimulate insulin production after a meal. Insulin, in turn, helps cells more efficiently use sugars from food. Too little insulin can lead to high levels of sugar in the blood, a symptom of diabetes. But higher blood sugar levels may also help fetuses grow. The new form of the gene may have given people an evolutionary advantage to survive famines, the researchers speculate.

At about the same time that the new form of GIP appeared, people in Europe and Asia were switching from a hunter-gatherer lifestyle to one based on agriculture. That switch may have exposed people to more frequent periods of famine, such as between harvests or when crops failed. The new version may have kept mothers’ blood sugar levels high enough to provide developing fetuses with energy to survive short periods of famine.

In the new study, the researchers tested whether the new form of the gene had any effect during pregnancy. Study coauthor Chia Lin Chang of Chang Gung University in Taiwan collected routine blood samples from 123 pregnant women. The team analyzed blood sugar concentrations and found that women with the new form of the gene had higher levels than women with the ancestral form.

Now the researchers want to test women from other populations to see if the gene acts the same way in everyone, and if it might help predict who is likely to develop gestational diabetes.

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