Alzheimer’s Disease Can Be Diagnosed Before Symptoms Emerge

Summary: A new study reveals it is not only possible to determine Alzheimer’s risks before symptoms appear, but it is also possible to determine who will deteriorate within the next few years.

Source: Lund University

A large study led by Lund University in Sweden has shown that people with Alzheimer’s disease can now be identified before they experience any symptoms. It is now also possible to predict who will deteriorate within the next few years.

The study is published in Nature Medicine, and is very timely in light of the recent development of new drugs for Alzheimer’s disease.

It has long been known that there are two proteins linked to Alzheimer’s—beta-amyloid, which forms plaques in the brain, and tau, which at a later stage accumulates inside brain cells. Elevated levels of these proteins in combination with cognitive impairment have previously formed the basis for diagnosing Alzheimer’s.

“Changes occur in the brain between ten and twenty years before the patient experiences any clear symptoms, and it is only when tau begins to spread that the nerve cells die and the person in question experiences the first cognitive problems. This is why Alzheimer’s is so difficult to diagnose in its early stages,” explains Oskar Hansson, senior physician in neurology at Skåne University Hospital and professor at Lund University.

He has now led a large international research study that was carried out with 1,325 participants from Sweden, the US, the Netherlands and Australia. The participants did not have any cognitive impairment at the beginning of the study. By using PET scans, the presence of tau and amyloid in the participants’ brains could be visualized.

The people in whom the two proteins were discovered were found to be at a 20-40 times higher risk of developing the disease at follow-up a few years later, compared to the participants who had no biological changes.

“When both beta-amyloid and tau are present in the brain, it can no longer be considered a risk factor, but rather a diagnosis. A pathologist who examines samples from a brain like this, would immediately diagnose the patient with Alzheimer’s,” says Rik Ossenkoppele, who is the first author of the study and is a senior researcher at Lund University and Amsterdam University Medical Center.

He explains that Alzheimer’s researchers belong to two schools of thought—on one hand, those who believe that Alzheimer’s disease cannot be diagnosed until cognitive impairment begins. There is also the group that he himself and his colleagues belong to—who say that a diagnosis can be based purely on biology and what you can see in the brain.

“You can, for example, compare our results to prostate cancer. If you perform a biopsy and find cancer cells, the diagnosis will be cancer, even if the person in question has not yet developed symptoms,” says Rik Ossenkoppele.

Recently, positive results have emerged in clinical trials of a new drug against Alzheimer’s, Lecanemab, which has been evaluated in Alzheimer’s patients. Based on this, the study from Lund University is particularly interesting, say the researchers:

“If we can diagnose the disease before cognitive challenges appear, we may eventually be able to use the drug to slow down the disease at a very early stage. In combination with physical activity and good nutrition, one would then have a greater chance of preventing or slowing future cognitive impairment.

“However, more research is needed before treatment can be recommended for people who have not yet developed memory loss,” concludes Oskar Hansson.

About this Alzheimer’s disease research news

Abstract

Amyloid and tau PET-positive cognitively unimpaired individuals are at high risk for future cognitive decline

A major unanswered question in the dementia field is whether cognitively unimpaired individuals who harbor both Alzheimer’s disease neuropathological hallmarks (that is, amyloid-β plaques and tau neurofibrillary tangles) can preserve their cognition over time or are destined to decline.

In this large multicenter amyloid and tau positron emission tomography (PET) study (n = 1,325), we examined the risk for future progression to mild cognitive impairment and the rate of cognitive decline over time among cognitively unimpaired individuals who were amyloid PET-positive (A⁺) and tau PET-positive (T⁺) in the medial temporal lobe (A⁺T_MTL⁺) and/or in the temporal neocortex (A⁺T_NEO-T⁺) and compared them with A⁺T⁻ and A⁻T⁻ groups.

Cox proportional-hazards models showed a substantially increased risk for progression to mild cognitive impairment in the A⁺T_NEO-T⁺ (hazard ratio (HR) = 19.2, 95% confidence interval (CI) = 10.9–33.7), A⁺T_MTL⁺ (HR = 14.6, 95% CI = 8.1–26.4) and A⁺T⁻ (HR = 2.4, 95% CI = 1.4–4.3) groups versus the A⁻T⁻ (reference) group. Both A⁺T_MTL⁺ (HR = 6.0, 95% CI = 3.4–10.6) and A⁺T_NEO-T⁺ (HR = 7.9, 95% CI = 4.7–13.5) groups also showed faster clinical progression to mild cognitive impairment than the A⁺T⁻ group.

Linear mixed-effect models indicated that the A⁺T_NEO-T⁺ (β = −0.056 ± 0.005, T = −11.55, P < 0.001), A⁺T_MTL⁺ (β = −0.024 ± 0.005, T = −4.72, P < 0.001) and A⁺T⁻ (β = −0.008 ± 0.002, T = −3.46, P < 0.001) groups showed significantly faster longitudinal global cognitive decline compared to the A⁻T⁻ (reference) group (all P < 0.001). Both A⁺T_NEO-T⁺ (P < 0.001) and A⁺T_MTL⁺ (P = 0.002) groups also progressed faster than the A⁺T⁻ group.

In summary, evidence of advanced Alzheimer’s disease pathological changes provided by a combination of abnormal amyloid and tau PET examinations is strongly associated with short-term (that is, 3–5 years) cognitive decline in cognitively unimpaired individuals and is therefore of high clinical relevance