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Evolution works in strange ways. What serves as an advantage at one point in time can sometimes prove a problem later, when the world has changed. It looks like that might be the case with type 2 diabetes, according to researchers from San Diego, California.
The researchers say that two or three million years ago, a gene called CMAH mutated in humans. The mutation made humans unable to produce one type of sialic acid molecule. All mammals except humans produce two types: N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc). The mutation in CMAH inactivated an enzyme that creates Neu5Gc by adding a single oxygen atom to Neu5Ac. As a result, humans, alone among mammals, do not have Neu5Gc.
The research group, whose work was published in The FASEB Journal, created mice with the human-like mutation in the CMAH gene, so that the mice could not create Neu5Gc. As a control, they had another group of mice with normal, functioning CMAH genes. Both groups of mice were fed a high-fat diet, and both became obese and developed insulin resistance. Only the mice with the CMAH gene mutation, however, experienced pancreatic beta cell failure, leading to type 2 diabetes.
What evolutionary advantage the mutation in the CMAH gene might have had millions of years ago is still a mystery. But it apparently has a distinct disadvantage now, in our environment of plenty.