The Biological Divergence: Why Sex Matters in Preclinical Alzheimer’s Disease
The epidemiological observation that women are disproportionately affected by Alzheimer’s disease (AD) has long been a subject of intense investigation. While increased longevity in women was once considered the primary driver, emerging evidence suggests that biological sex-specific pathways significantly influence the progression of AD pathology. A pivotal study recently published in JAMA Neurology (2026) by Coughlan et al. provides critical insights into this phenomenon, demonstrating that the relationship between amyloid-β (Aβ) and tau—the two hallmark proteins of AD—is fundamentally different in women compared to men. Understanding these differences is not merely an academic exercise; it is a clinical necessity for improving the accuracy of diagnostics and the efficacy of emerging anti-amyloid and anti-tau therapies.
Study Rationale and Methodology
The primary objective of the study was to investigate whether sex and aggregated Aβ synergistically predict levels of plasma phosphorylated tau 217 (p-tau217), a highly sensitive biomarker for early AD. Furthermore, the researchers investigated whether these p-tau217 levels serve as a more potent predictor of tau aggregation (measured via positron emission tomography [PET]) and subsequent cognitive decline in women compared to men. This is particularly relevant as p-tau217 is increasingly being adopted in clinical settings as a primary screening tool for AD pathology.
The researchers conducted a robust longitudinal analysis utilizing data collected between September 2024 and October 2025 from five major observational and clinical trial cohorts: the Anti-Amyloid Treatment in Asymptomatic Alzheimer’s Disease/Longitudinal Evaluation of Amyloid Risk and Neurodegeneration (A4/LEARN) cohort, the Harvard Aging Brain Study (HABS), the Wisconsin Registry of Alzheimer’s Prevention (WRAP), the Presymptomatic Evaluation of Experimental or Novel Treatments for Alzheimer’s Disease (PREVENT-AD), and the Alzheimer’s Disease Neuroimaging Initiative (ADNI).
The study included a total of 1,292 participants (63.6% women) with a mean age of 70.6 years. All participants were cognitively unimpaired at baseline and had undergone multiple assessments via tau PET imaging and plasma p-tau217 assays. Cognitive performance was tracked using the Preclinical Alzheimer Cognitive Composite (PACC) over an average follow-up period of 4.6 years, while the mean follow-up for tau PET assessments was 3.6 years.
Key Findings: The Synergistic Effect of Sex and Amyloid on P-Tau217
The analysis revealed a significant sex-by-amyloid interaction regarding p-tau secretion. At higher levels of aggregated Aβ (measured in Centiloids), women exhibited significantly higher baseline plasma p-tau217 levels compared to age-matched men (β, -0.21 [95% CI, -0.37 to -0.05], P = .009). The highest interaction effect was observed in the A4/LEARN cohort. This suggests that for a given burden of amyloid plaques, the female brain is more likely to trigger the phosphorylation and secretion of tau into the bloodstream, marking an earlier and more aggressive pathological response.
Cross-sectional and Longitudinal Tau PET Interaction
The study further investigated how these plasma p-tau217 levels correlated with the actual deposition of insoluble tau tangles in the brain. The results showed that p-tau217 levels were more strongly associated with tau PET signals in women across multiple brain regions:
1. Cross-sectional Interaction: At baseline, significant sex × p-tau217 interactions were identified in several cohorts, including HABS, A4/LEARN, WRAP, and PREVENT-AD. In these regions, women showed higher tau PET deposition than men at equivalent p-tau217 levels.
2. Longitudinal Interaction: The rate of tau accumulation over time was significantly faster in women at higher p-tau217 levels across all five cohorts. Specifically, longitudinal interactions were significant for 4 regions in A4/LEARN, 5 regions in both ADNI and WRAP, and 2 regions in HABS and PREVENT-AD. These findings indicate that once the tau-secreting process begins, the spread of tau tangles through the brain occurs more rapidly in women.
Impact on Cognitive Decline
The researchers also examined the functional consequences of these pathological differences. Using the PACC score, the secondary analysis revealed that women with higher baseline p-tau217 levels experienced significantly faster rates of cognitive decline than men. This interaction was particularly pronounced in the WRAP and ADNI cohorts. The data suggests that the physiological buffer or cognitive reserve that might otherwise protect individuals with early pathology is more quickly overwhelmed in women due to the accelerated accumulation of tau tangles, which are more closely linked to neuronal death than amyloid plaques alone.
Mechanistic Insights and Biological Plausibility
The findings add to a growing body of evidence suggesting that women have a differential tau response to Aβ that may emerge at the point of p-tau secretion. Several biological mechanisms may underpin this divergence:
1. Endocrine Influence: The transition through menopause involves a sharp decline in 17β-estradiol, which has neuroprotective properties. Estrogen is known to modulate tau phosphorylation and facilitate the clearance of protein aggregates. Its loss may leave the brain more vulnerable to amyloid-induced tauopathy.
2. Genetic Factors: The MAPT gene and other regulatory genes may be subject to sex-specific epigenetic regulation. Additionally, genes on the X-chromosome that escape inactivation could contribute to the higher protein burden observed in women.
3. Innate Immunity: Sex differences in microglial activation and neuroinflammation may play a role. If female microglia respond more aggressively to amyloid plaques, they may inadvertently facilitate the seeding and spreading of tau pathology through the extracellular space.
Clinical Implications for Diagnostics and Therapeutics
These findings have immediate implications for the management of preclinical Alzheimer’s disease:
1. Refining Biomarker Thresholds: The clinical community may need to consider sex-specific cut-offs for p-tau217. A value that indicates moderate risk in a man could indicate a high risk of rapid progression in a woman.
2. Precision in Clinical Trials: Recruitment and stratification in clinical trials for anti-tau therapies should account for these sex differences. Women may have a narrower window for intervention before tau pathology becomes widespread.
3. Patient Counseling: Clinicians can use these data to provide more personalized risk assessments for patients presenting with amyloid positivity in preclinical stages.
Conclusion
The study by Coughlan et al. provides a compelling biological explanation for the sex disparities observed in Alzheimer’s disease. By demonstrating that women exhibit higher p-tau217 levels and faster tau PET accumulation in response to amyloid-β, the research shifts the focus from simple longevity to sex-specific pathological trajectories. Addressing these biological differences is essential for the development of precision medicine strategies that can effectively stall the progression of Alzheimer’s disease in both men and women.
Funding and Clinical Trial Registry
This study was supported by the National Institutes of Health, the Alzheimer’s Association, and various philanthropic foundations. Data were utilized from the A4 Study (NCT02008357) and the Alzheimer’s Disease Neuroimaging Initiative (ADNI; NCT00106639).
References
Coughlan GT, Ourry V, Townsend D, et al. Sex Differences in P-Tau217, Tau Aggregation, and Cognitive Decline. JAMA Neurol. 2026 Feb 16:e255670. doi: 10.1001/jamaneurol.2025.5670.