It's not just professional athletes and soldiers who are at risk from traumatic brain injury. More than 1.7 million people a year sustain a traumatic brain injury, and about 50,000 of them die each year, according the Centers for Disease Control. There are both emotional and financial costs from these injuries.

My sister learned she was a carrier for a recessive disease, Bloom syndrome, late in one of her pregnancies. I remember the panicked call and the weeks of worry as she and her husband awaited his test results; if he was also a carrier, this meant their daughter had a one in four chance of being born with the disorder.

It's worth knowing more about the complicated environmental and genetic factors that could explain why traumatic brain injuries lead to long-term disabilities in some people and not in others.

Anne Wojcicki Quotes