FILE - In this Aug. 14, 2018 file photo, a doctor looks at a PET brain scan at the Banner Alzheimers Institute in Phoenix. Two…
FILE - In this Aug. 14, 2018 photo, a doctor looks at a PET brain scan at the Banner Alzheimers Institute in Phoenix.

Two experimental drugs failed to prevent or slow mental decline in a study of people who are virtually destined to develop Alzheimer's disease at a relatively young age because they inherited rare gene flaws.

The results announced Monday are another disappointment for the approach that scientists have focused on for years — trying to remove a harmful protein that builds up in the brains of people with Alzheimer's, the leading cause of dementia.

"We actually don't even know yet what the drugs did" in term of removing that protein because those results are still being analyzed, said study leader Dr. Randall Bateman at Washington University in St. Louis, Missouri.

But after five years on average, the main goal of the study was not met: people on either of the drugs scored about the same on thinking and memory tests as others given placebo treatments.