02/03/2026
A great informative post by Kerry Bone.
A new analysis led by researchers at University College London (UCL) suggests that Alzheimer disease (AD) may depend far more heavily on one gene than scientists once believed. The study estimates that more than 90% of Alzheimer cases might not develop without the influence of a single gene called APOE. Moreover, the impact appears to extend beyond AD alone. Researchers found that nearly half of all dementia cases may also rely on this gene’s contribution.
The APOE gene has been linked to Alzheimer’s disease for many years. It exists in three common forms, or alleles, known as ε2, ε3, and ε4. Each person inherits two copies of APOE, which results in six possible combinations of these variants. The six combinations of the APOE gene are: ε2+ε2; ε2+ε3; ε2+ε4; ε3+ε3; ε3+ε4; ε4+ε4. The variants are more commonly referred to as APOE2, APOE3, APOE4, which more correctly describes the APOE protein type produced from the gene (apolipoprotein E). APOE4 is thought to be the ancestral form; APOE3 and APOE2 evolved later.
Research in the 1990s established that people who carry one or more ε4 variants (producing mainly APOE4) face a much higher risk of AD compared with those who have two copies of the more common ε3 variant. People with ε2 generally had a lower risk than ε3 carriers. However, the new study goes much further than this.
Lead author Dr. Dylan Williams (UCL Division of Psychiatry and Unit for Lifelong Health and Ageing at UCL) said: “We have long underestimated how much the APOE gene contributes to the burden of Alzheimer’s disease. The ε4 variant of APOE is well recognised as harmful by dementia researchers, but much disease would not occur without the additional impact of the common ε3 allele, which has been typically misperceived as neutral in terms of Alzheimer’s risk.
“When we consider the contributions of ε3 and ε4, we can see that APOE potentially has a role in almost all Alzheimer’s disease. Consequently, if we knew how to reduce the risk that the ε3 and ε4 variants confer to people, we may be able prevent most disease from occurring.”
The study represents the most detailed modelling so far of how common APOE variants contribute to Alzheimer’s and dementia across the population. Researchers combined evidence linking the ε3 and ε4 alleles to Alzheimer’s disease, all-cause dementia, and the brain changes that precede Alzheimer’s.
A critical element of the analysis was access to data from four very large studies involving more than 450,000 participants. This allowed researchers to identify a sizable group of people with two ε2 copies, an uncommon but low risk group, and use them as a reference point in their calculations for the first time in this type of research. Specifically, the researchers analysed electronic health record data from 171,105 older adults in the UK Biobank cohort and 289,150 older adults in the FinnGen study to determine Alzheimer and all-cause dementia diagnoses. They also examined baseline amyloid PET scans of 4,415 participants in the A4 trial and analysed data from 5,007 participants in the Alzheimer's Disease Genetics Consortium (ADGC) of autopsy-confirmed Alzheimer cases and controls to provide a comprehensive view.
Based on their analysis, the researchers estimated that 72 to 93% of Alzheimer cases would not have occurred without the ε3 and ε4 variants of APOE. They also found that roughly 45% of all dementia cases might not arise without the gene’s influence.
These estimates exceed earlier assessments of APOE’s impact, largely because the new study evaluated the combined effects of both ε3 and ε4 rather than focusing only on ε4.
Results differed somewhat across the four studies included in the analysis. These differences reflected how AD and dementia were defined and measured, including whether cases were identified through medical diagnoses, other dementia classifications, or signs of amyloid buildup seen on brain scans. Variation in follow-up length and possible recruitment biases also contributed. When considered together, the evidence suggests that APOE is likely responsible for at least three quarters of Alzheimer cases, and potentially more.
The findings indicate that APOE should receive greater attention in research aimed at understanding disease mechanisms and developing new treatments and prevention options.
APOE is a lipoprotein-binding protein that helps transport cholesterol, triglycerides and phospholipids. It acts as a ligand for LDL (low density lipoprotein) receptors and related receptors, helping shuttle lipids between tissues, particularly the brain, the vascular system and the liver. In the brain, APOE is produced mainly by astrocytes and helps redistribute cholesterol to neurons for membrane repair and synapse maintenance.
The APOE ε4 variant is thought to increase dementia risk by impairing amyloid-β clearance, amplifying tau pathology and neuroinflammation, disrupting brain lipid transport and synaptic repair, and compromising vascular integrity, thereby lowering the brain’s resilience to age-related neurodegenerative stress over time. Further research is needed to confirm these processes and to explain why ε3 increases dementia risk compared with ε2.
Despite its strong influence, APOE is not the sole cause of Alzheimer or other dementias. Even among people with the highest genetic risk, those who carry two ε4 variants, lifetime risk of AD is still estimated to be below 70%. See my recent posting on the 14 modifiable risk factors in AD and the key role they play.
This invites some more sober commentary on the study’s findings. For example, claiming that most Alzheimer cases would not occur without the contribution of APOE was a bit like saying most road traffic deaths wouldn't occur without the contribution of cars, according to geneticist Dr Timothy Frayling of the University of Geneva. (This is not entirely true because only ε3 and ε4 appear to account for risk.) "People should not worry if they have the risk versions of the gene, because 99.4% of us do," he added.
To my mind, the true value of this study lies in the mechanistic lens it provides. Specifically, are there any natural interventions that can mitigate the risk imposed by APOE variants? See my next posting for a few promising leads.
For more information see: https://bit.ly/40837KO
and
https://scitechdaily.com/one-overlooked-gene-may-shape-nearly-all-alzheimers-risk/
