Alzheimer’s is usually framed as a brain-first disease: misfolded proteins build up, neurons suffer, memory fades. But a new genomic analysis points to a very different starting point.
Instead of beginning in the brain, the earliest sparks of Alzheimer’s disease may be caused by inflammation in “barrier” organs like the skin, lungs, or gut.
Evidence shows this may happen decades before anyone forgets a name or loses their way home.
If this analysis is correct, it could also help explain something that has frustrated families and researchers for years: why Alzheimer’s drugs have so often disappointed.
Many treatments go after amyloid or tau once the disease is already well underway. This new work suggests we may be arriving late to the fire – treating the smoke while the match was lit somewhere else long ago.
Inflammation and Alzheimer’s risk
This “whole-body” framing isn’t completely out of nowhere. A growing number of studies have been hinting that immune activity and inflammation are tied to dementia risk.
What’s new here is the scale and specificity. The researchers traced Alzheimer’s risk genetics across many tissues and cell types and found that a surprising amount of the signal sits outside the brain.
The team, led by César Cunha at the Novo Nordisk Foundation Center for Basic Metabolic Research in Denmark, pulled together an enormous dataset.
They compared genetic data from more than 85,000 people with Alzheimer’s and around 485,000 people without it, using the European Alzheimer and Dementia Biobank.
Then, the experts went a step further: they analyzed gene activity across roughly 5 million single cells, covering 40 body regions and 100 brain regions.
That let the researchers ask a very direct question: where in the body are the genes associated with Alzheimer’s risk actually active? They focused on around 1,000 genes that contain variants known to raise Alzheimer’s risk.
Risk genes with low brain signals
Here’s the twist that made the researchers pause: many of these risk genes showed very low activity in brain cells, but much stronger activity in other organs – including the skin, lungs, digestive system, spleen – and in immune cells circulating in the blood.
Cunha said he initially suspected an error because the brain signal looked so weak. But after repeating and expanding the analyses, the pattern held.
A lot of Alzheimer’s genetic risk seems to be “spoken” most loudly in the immune system and in organs that constantly deal with the outside world.
That matters because many of these genes are involved in immune regulation – the machinery that controls inflammation.
Inflammation in barrier tissues
The study found many risk genes were especially prevalent in barrier tissues like the skin, lungs, and gut.
These tissues are on the front line every day, responding to microbes, allergens, toxins, and irritation. They’re built to mount inflammatory responses and sometimes, those responses become chronic or exaggerated.
The implication is provocative: genetic variants might influence how strongly someone’s body reacts to infections or inflammatory triggers in these tissues, and whether that immune activity eventually spills over into the brain.
In this view, a person with inherited risk variants might be more vulnerable to a “chain reaction” set off by something that doesn’t seem neurological at all, such as a respiratory infection or a gut inflammation episode.
The damage might only show up as cognitive decline years later.
The inflammation link to Alzheimer’s
One detail the team found especially striking was age-related timing. They saw the highest expression of these Alzheimer’s-linked variants around ages 55 to 60.
That suggests midlife may be a particularly sensitive period when inflammation is more likely to leave long-term marks.
This lines up with earlier evidence. A long-running study in Hawaii found that men with higher inflammatory markers in their blood in their late 50s were more likely to develop Alzheimer’s decades later.
According to Cunha, a significant inflammatory hit in your late 50s – for example, a viral lung infection – might set processes in motion that only become visible as dementia 20 or 30 years later.
He also stressed that the mechanism is still unclear, and a big part of the puzzle remains unsolved.
Genes aren’t destiny
Other researchers have been circling similar signals. Rezanur Rahman from QIMR Berghofer Medical Research Institute in Australia recently found that Alzheimer’s-linked variants seem to cluster in the skin and lungs as well.
But he cautioned that genetic association alone doesn’t prove those genes are functionally driving disease. In other words, the pattern is compelling, but it’s not a smoking gun yet.
That’s an important reality check. This study strengthens a hypothesis but it doesn’t close the case.
Shifting Alzheimer’s focus to inflammation
Cunha says the challenge now is getting the Alzheimer’s field to seriously widen its focus. He describes how strongly amyloid has dominated conference conversations for decades – to the point where anything outside that framework can be dismissed as “not really Alzheimer’s.”
That kind of scientific inertia is understandable. If you’ve spent 30 years chasing a particular mechanism, shifting your mental model isn’t easy.
But the new data add weight to a growing idea: Alzheimer’s may be less like a brain-only disorder and more like a long, slow systemic process, with the brain being where the damage finally becomes visible.
If that’s true, the most important years for prevention might come long before the first memory test ever looks abnormal.
A preprint of the study is published in MedRxiv.
—–
Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.
Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.
—–