He wavers about getting tested.

“Sometimes I think, ‘This is a terrible storm on the horizon that could absolutely devastate us, and I want to know if it is real or not.’ Other times I say, ‘Gosh, if I do find out that it is real and I know I will die that way and I know probably the age I will die — that is an almost unbearable amount of information about my future.’”

“People say you could go sky diving or ride a bull. But you can only do things like that as long as time and income provide. You still have to get up in the morning and go to work and pay your bills.”

He joined a study at the Washington University School of Medicine in St. Louis in which researchers are following members of families with the genes for early-onset Alzheimer’s disease. At a recent meeting, he recalled, he found himself in a room full of people like himself: All had a parent with an Alzheimer’s gene.

All were at risk of having the mutated gene themselves.

Mr. Reiswig asked the group, “How many have been tested?”

Half raised their hands.

“Of those of you who have been tested, how many regret it?”

He was met with ominous silence.

Then a man spoke up. He said he had been tested and learned he has the gene.

As for regrets, “it depends on the day,” the man said. “I have battled weight issues and the suicide issue, and I have had problems with my marriage ever since I found out. Some days I really regret it. It is a huge burden. Other days I am glad I know.”

Mr. Reiswig has been thinking it over. He has decided not to be tested.

“For me, the return is not worth the investment,” he said.