A team at Washington University School of Medicine has assembled a “timeline” of the unseen progress of Alzheimer’s before symptoms appear.
Scientists looked at families with a genetic risk of the disease.
Writing in the New England Journal of Medicine, they say signs appeared up to 25 years before the expected onset of the disease.
The 128 people in the study, from the UK, US and Australia, had a 50% chance of inheriting one of three mutations that are certain to cause early Alzheimer’s, which often develops in people’s 30s and 40s – much earlier than the more common form of Alzheimer’s which generally affects people in their 60s.
Those who carry the mutations will go on to develop the disease.
The researchers looked at the age the participants’ parents were when they developed the disease – and therefore how many years it was likely to be before they too showed symptoms.
They underwent blood and spinal fluid tests as well as brain scans and mental ability assessments.
The earliest change – a drop in spinal fluid levels of the key ingredient of Alzheimer’s brain plaques – can be detected 25 years before the anticipated age of disease onset, they suggest.
At 15 years, raised levels of tau, a structural protein in brain cells can be seen in spinal fluid – and shrinkage can also be detected within parts of the brain.
Changes in the brain’s use of the sugar glucose and slight memory problems become apparent 10 years before symptoms would appear, they suggest.
Researchers also tested other members of the families without the inherited mutations – and found no changes in the markers they tested for.