As a boy, Gary Reiswig would take his grandfather by the hand and guide him on walks around the family farm in western Oklahoma.

At 5, Gary knew to avoid the prairie dog town, fearful that his grandfather might stumble over one of the holes that the rodents burrowed into the grassy plain.

Occasionally, his grandfather would stop. His eyes took on an eerie stare that spoke of an empty place - one that once was filled with memories, laughter and toil.

In 1945, nobody knew that Gary’s grandfather had a rare form of Alzheimer’s disease that would strike 10 of Gary’s 14 aunts and uncles, his father and his only brother and sister in the prime of their lives.

Gary’s family has dominantly inherited Alzheimer’s disease. It is rare, and it afflicts the young. In his family, symptoms can appear in the early 40s.

This inherited form of Alzheimer’s is caused by mutations in one of three genes: amyloid precursor protein, presenilin 1 or presenilin 2. It is the only form of Alzheimer’s for which there is a diagnostic test that can predict with certainty whether Alzheimer’s will ensue.

That may change. Researchers, patient advocates and policy makers are pushing for earlier testing of Alzheimer’s, in part because it will help the search for a cure. That means more people could find out if they will succumb to the disease.

But without a treatment or a cure, would people want to know?

Surprisingly, yes, said Dr. Robert Blendon, professor of health policy and political analysis at the Harvard School of Public Health.

Blendon conducted a survey of 2,678 adults from five countries that was released on Wednesday at the Alzheimer’s Association International Conference in Paris. About two thirds of respondents said they were likely to get a test to predict whether they would get Alzheimer’s before any symptoms appeared.

Some 35.6 million people worldwide have Alzheimer’s, the most common form of dementia. Drugs only help symptoms; none can arrest Alzheimer’s, which costs $604 billion a year globally to treat.

All of the drugs that have been tried in people with advanced dementia have failed to slow the disease, and many experts think the reason is that they were tried on people who were too far gone.

Some people who know Alzheimer’s may lie in wait make different life choices. They take more extravagant vacations, they put their finances in order earlier than many other people. They even may use a surrogate parent instead of taking a chance of passing on the disease to a new generation.