We all know that nobody's perfect. But now scientists have documented that fact on a genetic level. Researchers discovered that normal, healthy people are walking around with a surprisingly large number of mutations in their genes.
It's been well known that everyone has flaws in their DNA, though, for the most part, the defects are harmless. It's been less clear, however, just how many mistakes are lurking in someone's genes. "It's such an interesting question that people had been trying to make estimates from indirect approaches for a long time," says Chris Tyler-Smith of the Wellcome Trust Sanger Institute in Cambridge, England. "There were estimates that ranged from just a handful up to 100 or more serious disease-associated mutations."
But Tyler-Smith and his colleagues wanted to get a more precise, direct estimate. So they analyzed the DNA of 179 people from the United States, Japan, China and Nigeria who had volunteered to have their entire genetic blueprints deciphered through the 1,000 Genomes project. Now, in a paper appearing in the American Journal of Human Genetics, the researchers are reporting a big surprise.
"We found quite amazingly large numbers of deleterious and known disease-causing mutations," Tyler-Smith says. According to their analysis, the average person has around 400 defects in his or her genes, including at least a couple that are associated with disease.
The weird thing is, none of the people whose DNA was studied were severely sick. They all seemed perfectly happy and healthy. "It could be that in many cases the other copy of that gene or a similar gene within a multi-gene family takes over," Tyler-Smith says. "It's a bit surprising that people should be walking around apparently healthy yet we're seeing known disease-causing mutations in their genomes," he says. "But the answer was that these tended to be for mild and very often late-onset conditions. Things like heart disease, an increased risk of developing cancer."