Can knowing you and your family may get Alzheimer’s ever be positive?

At the University of Washington’s School of Medicine there is a computer database that states with certainty – albeit heavily encrypted – whether or not Sophie Leggett will develop a form of genetically inherited early onset Alzheimer’s disease. But she has chosen not to find out what it says.

A blood test is available to adult children and siblings of those who develop Alzheimer’s at a young age and have a family history of the disease. It identifies whether they carry one of the three faulty genes known to cause familial early onset Alzheimer’s, presenilin 1 (the mutation affecting Leggett’s family), presenilin 2 and amyloid precursor protein. All result in the overproduction of amyloid, a protein that builds up into the plaques on the brain which are the hallmark of Alzheimer’s.

Now 39, Leggett saw her mother and aunt develop familial early onset Alzheimer’s in their early 40s – as had their father. All died in their 50s. There is a one-in-two chance that Leggett has inherited the gene mutation.

“I focus on the 50% chance that...