This family carried a rare mutation that should have been lethal. What was keeping them alive?

^{Patrick J. Lynch, medical illustrator,
CC BY 2.5 >, via Wikimedia Commons}

The result didn’t make sense. The researcher kept scanning the mouse’s pregnant belly, back and forth, back and forth. They could see the embryos on the ultrasound screen, cocoon-like, in grayscale — but there were no heartbeats. It should’ve been visible by now, at eight and a half days, a rhythmic flashing, a clue that the organ was on its way. Instead, each outline was utterly still, dead before it had come to life.

That couldn’t be right. These mice carried the exact same genetic mutation as a family who lived about an hour away, in the county outside Pittsburgh, near the West Virginia line. The humans definitely had beating hearts. Nicole Burns worked at an assisted living facility, hoisting residents in and out of bed, guiding them as they shuffled to dinner with a firm hand on the back. Her daughter Peyton loved hunting. Her son Cameron loved playing basketball. Their genome couldn’t contain something so lethal: They were all very much alive.

The researchers tried again...