A new study has found that an experimental drug appears to reduce the risk of Alzheimer’ s-related dementia in people destined to develop the disease in their 30s, 40s, or 50s.

The findings suggest — for the first time in a clinical trial — that early treatment to remove amyloid plaques from the brain many years before symptoms arise can delay the onset of Alzheimer’s dementia.

The study has been published in The Lancet Neurology.

The international study involved 73 people with rare, inherited genetic mutations that cause the overproduction of amyloid in the brain, all but guaranteeing that they will develop Alzheimer’s disease in middle age.

For a subgroup of 22 participants who had no cognitive problems at the study’s start and who received the drug the longest — an average of eight years — the treatment lowered the risk of developing symptoms from essentially 100% to about 50%, according to a primary analysis of the data and supported by multiple sensitivity analyses supporting the trend.

“Everyone in this study was destined to develop Alzheimer’s disease and some of them haven’t yet,” said senior author Randall J. Bateman, MD, the Charles F. and Joanne Knight Distinguished Professor of Neurology at WashU Medicine.

“We don’t yet know how long they will remain symptom-free — maybe a few years or maybe decades. In order to give them the best opportunity to stay cognitively normal, we have continued treatment with another anti-amyloid antibody in hopes they will never develop symptoms at all. What we do know is that it’s possible at least to delay the onset of the symptoms of Alzheimer’s disease and give people more years of healthy life.”

The findings provide new evidence to support the so-called amyloid hypothesis of Alzheimer’s disease, which posits that the first step on the road to dementia is the build-up of amyloid plaques in the brain and that removing such plaques or blocking their formation can stop symptoms from arising.

For this study, Bateman and colleagues evaluated the effects of an experimental anti-amyloid drug to see if the medication could prevent the development of dementia.

The study population consisted of people who had originally enrolled in the Knight Family DIAN-TU-001, the first Alzheimer’s prevention trial in the world, and then continued into an extension of the trial in which they received an anti-amyloid drug.

Currently led by Bateman and funded primarily by the Alzheimer’s Association, GHR Foundation and the National Institutes of Health (NIH), the Knight Family DIAN-TU-001 was launched in 2012 to evaluate anti-amyloid drugs as preventive therapies for Alzheimer’s disease.