ST. LOUIS (AP) — They lovingly call each other X-Men, named after the comic book team of mutant superheroes.

They have a rare genetic form of Alzheimer's disease that makes up just 1 percent of cases. It strikes early — in their 30s and 40s — and decimates families.

Those with the genetic mutation have a near certainty they will develop the disease and a 50 percent chance of passing it on to their child.

"It felt like, in one tiny moment, a giant guillotine chopped 30 years off my life and our future," said Jetske van der Schaar, 37, from Holland, while giving a speech with her boyfriend at an...