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, while giving a speech with her boyfriend at an annual conference for families with the mutation.

When van der Schaar learned she had the mutation, she was watching her own heartbreaking future unfold while caring for her mother, who died of Alzheimer’s in her early 50s.

It’s no comic book. But to researchers, these families are heroes. They may be the key to treating and even curing Alzheimer’s disease.

They have provided answers about how the deadly brain disease progresses, starting 20 years or more before the first symptoms appear.

They are the participants in the first study to test whether drugs can prevent Alzheimer’s dementia or slow its onset, rather than trying to treat the disease after symptoms have set in.

Today, Washington University leads an observational network of 537 study participants at 20 study sites across the world and drug research at 41 international sites. The federal government has provided a total of nearly $200 million in funding.

At the end of this year, the drug study will be complete, and much-anticipated findings will be released soon after. Another study is expected to begin, one that tests giving prevention medications even earlier — to patients as young as 18.

“This will be an extremely important clinical trial. It could have a dramatic impact,” said Dr. Eric McDade, Washington University associate director of the drug prevention research.

Scientists are hopeful they will be able to apply the findings to the more common, but much harder to study, sporadic Alzheimer’s disease. An estimated 5.7 million Americans are living with Alzheimer’s dementia. It is the sixth-leading cause of death and the leading cause of disability.

“You are the true inspiration,” Alzheimer’s Association President Harry Johns said last summer to the families at their annual conference in Chicago. “You are the real champions who will ultimately make a difference and realize the answers so much of the world needs.”

Since 2015, the families and the researchers studying them have met annually. They help each other cope, find strength and fight in their own way. Together, they feel they can change the trajectory of the disease.

Tests of spinal fluid reveal that the telltale amyloid beta and tau proteins of Alzheimer’s disease become elevated long before signs of cognitive impairment.

In the early 2000s, researchers began to wonder: Do elevated levels mean for certain a person will become demented? Do factors protect some people? When do you test for abnormal levels? Could doctors intervene somehow?

In 2008, the university launched the Dominantly Inherited Alzheimer Network, and in 2012, the next phase of research began: testing whether drugs could prevent dementia in people with the mutation.

The research started with two different drugs: antibodies that either removed amyloid beta plaques or prevented the plaques from forming. A third drug was added later — an inhibitor that blocked amyloid beta from being produced.

Seventy-five percent of the participants get one of the drugs; 25 percent get a placebo. Participants do not have to know their genetic results to be in the study. Those without the mutation are placed in the placebo group.

The trials unit is unique in Alzheimer’s research because it is adaptive. When a drug is ineffective, another drug can be introduced without having to start over. An effective medication would be a major breakthrough.

Despite decades and billions of dollars in research, there is no cure and few medications to treat dementia. The last Alzheimer’s drug was approved more than 15 years ago and brings only temporary relief of symptoms. Some drug companies have abandoned their research efforts.

The failure may be because once brain atrophy and symptoms have begun, it is too late. Early drug intervention in those with dominantly inherited Alzheimer’s disease — who are almost certain to get dementia but don’t yet have symptoms — is the only way to easily test this theory. Scientists have been unable to replicate Alzheimer’s in an animal model.