Fetal mutations may start immediately

Immediately after conception, the cells in a fetus can begin to accumulate tiny genetic mutations—the kinds of changes that occur throughout life and may lead to diseases such as cancer. So conclude researchers who analyzed differences among fetal human brain cells, as published Dec. 7 in Science.

Brain precursor cells isolated from a single fetus, they found, already had genetic differences. Overall, each cell had accumulated 200 to 400 small genetic mutations—an average of one mutation per cell division beginning at fertilization. The mutation rate increases dramatically during neurogenesis. Some mutations were found to arise so early in development that a fetus’ sex cells have not yet fully formed, suggesting that the mutations could be passed along to future offspring.

“This opens up a larger perspective on human development,” says co-corresponding author Flora M. Vaccarino, MD, Harris Professor in the Yale Child Study Center and professor of neuroscience. “Some of our genome does not come from our parents.” It explains one reason identical twins can have different physical traits, and may point toward new explanations for childhood neurodevelopmental disorders.