\Not every cell in the body carries the same DNA, writes Carl Zimmer at the New York Times.
People are, he says, mosaics.
Zimmer notes that there's increasing evidence that mosaicism does have a role in disease. For instance, researchers examining patients with hemimegalencephaly —one side of their brains are larger than the other — found that some brain cells from patients shared the same mutation, but other cells lacked the mutation, he says.
At the same time, Zimmer says, mosaicism is "the norm." Researchers at Oregon Health & Science University found in a study of children and adults with and without liver disease that a some of their cells were aneuploid and, similarly, Wellcome Trust Sanger Institute researchers found in a cohort of 241 women that each had acquired mutations that were present in a portion of cells, he notes. Others have found mosaicism within neurons, but its effect is isn't clear, Zimmer adds.
"What we do know is that mosaicism introduces randomness into the development of our brains. Mutations, which arise at random, will form different patterns in different people," he writes.