A Parkinson’s Protein Makes Alzheimer’s Progress 20 Times Faster in Women

Women account for nearly two-thirds of Alzheimer's cases in the United States, a disparity researchers have long struggled to fully explain. A new Mayo Clinic study published in JAMA Network Open adds a striking piece to that puzzle: a protein associated with Parkinson's disease appears to accelerate Alzheimer's-related brain changes up to 20 times faster in women than in men. The finding is preliminary, but if it holds up in larger studies, it could fundamentally reshape how clinicians screen and treat Alzheimer's in women.

Alpha-synuclein drives tau buildup at 20x the speed in women

The core finding centers on two proteins. Tau is a well-known hallmark of Alzheimer's: it misfolds, clumps, and tangles inside neurons, gradually destroying them. Alpha-synuclein is better known for its role in Parkinson's disease and Lewy body dementia, but roughly half of all Alzheimer's patients also have abnormal, misfolded forms of it in their brains. When researchers tracked how these proteins interacted over time in 415 participants (ranging from cognitively healthy adults to people with mild cognitive impairment or dementia), they found that alpha-synuclein positivity was associated with tau accumulation proceeding over 20 times faster in women than in men with the same protein abnormality. Alpha-synuclein, in other words, appeared to act as an accelerant specifically in female brains. "When we see disease-related changes unfolding at dramatically different rates, we cannot keep approaching Alzheimer's as though it behaves exactly the same way in everyone," said Kejal Kantarci, the study's lead researcher.

Why women with Parkinson's face a disproportionate amyloid burden

A companion autopsy analysis, drawing on 230 confirmed Parkinson's disease cases from the Arizona Study of Aging and Neurodegenerative Disorders, reinforced the imaging results from a different angle. Women with Parkinson's carried significantly heavier amyloid plaque loads than their male counterparts: mean cortical total plaque scores were 6.5 in women versus 4.9 in men. High plaque burden was present in 56.8 percent of women but only 39.7 percent of men. Women were also more than twice as likely to have a high amyloid burden overall, with an odds ratio of 2.18. Interestingly, a higher proportion of men tested positive for misfolded alpha-synuclein (21.5 percent versus 12 percent in women), yet the protein's downstream impact was far more damaging in women when it was present. Researcher Elijah Mak noted that "this opens an entirely new direction for understanding why women bear a disproportionate burden of dementia."

This sex-specific vulnerability aligns with emerging evidence that Parkinson's disease follows different brain-aging trajectories in men and women, and that sex differences in early Parkinson's brain atrophy appear from the earliest stages of diagnosis. One working hypothesis involves estrogen: the hormone may protect against toxic protein accumulation, and the sharper, more sudden drop in estrogen that women experience in later life could leave the brain more vulnerable to the kind of cascade the new study describes. Misfolded alpha-synuclein may then act as a second-hit amplifier, increasing neuroinflammation and worsening tau clumping in brain tissue already deprived of hormonal protection.

How researchers measured protein buildup and plaque load

The imaging-based arm of the study used advanced brain imaging and cerebrospinal fluid testing to identify protein biomarkers over time. Alpha-synuclein positivity was measured using a cerebrospinal fluid seed amplification assay, a technique that detects the presence of misfolded protein even at low concentrations. The autopsy arm cross-referenced those findings against direct tissue analysis of confirmed Parkinson's cases, allowing the team to link protein profiles observed in life to physical plaque burdens measured after death. Plasma biomarkers including phosphorylated-tau181 have separately shown promise in identifying underlying Alzheimer's pathology in Parkinson's patients, suggesting that fluid-based screening could one day flag high-risk individuals before significant cognitive decline sets in.

Short follow-up and small samples leave key questions open

The study authors are careful to note that the research does not establish cause and effect. The median follow-up period for protein tracking was approximately 1.23 years, which is relatively short for capturing the full arc of neurodegeneration. Sample sizes in both arms of the analysis are also modest, meaning the observed sex differences, though statistically significant, need replication in larger cohorts before they can guide clinical practice. Dr. Erika Driver-Dunckley, commenting on the autopsy findings, observed that "it may be that a larger study would pick up cognitive differences related to the increased plaque load." Whether the accelerated tau accumulation seen in women translates to faster cognitive decline, and on what timeline, remains an open question. Cross-sectional work has consistently shown sex differences in Parkinson's brain atrophy at baseline, but longitudinal data tracking outcomes over years is still needed.

Rethinking Alzheimer's screening and treatment for women with Parkinson's

If the findings are confirmed, the practical implications are significant. Women with Parkinson's disease may need routine screening for Lewy body proteins, not just standard Alzheimer's biomarkers, to accurately predict their disease trajectory. Treatment protocols developed largely on mixed-sex or male-dominant cohorts may underestimate the speed at which Alzheimer's pathology can unfold in women who also carry alpha-synuclein abnormalities. Alzheimer's, as the researchers frame it, is not a one-size-fits-all disease, and co-pathologies may fundamentally alter the disease process in ways that sex-blind study designs cannot capture. The next steps involve longer follow-up studies and larger clinicopathological series that can disentangle biological mechanism from statistical noise. What this study makes hard to ignore is the possibility that for millions of women at the intersection of Parkinson's and Alzheimer's risk, the biological clock may be running considerably faster than current models assume.

Evidence rating

INVESTIGATIONAL — 57/100

Caveats:

• Funding not disclosed; independent replication has not been confirmed.
• Observational design; shows association, not causation.
• Single study — findings have not been replicated in an independent cohort.

Observational study examining sex differences in the co-occurrence of Alzheimer's-related neuropathology among individuals with Parkinson's disease. The design establishes association only, not causation, and the findings have not yet been replicated in an independent population. Funding was not disclosed.

References

1. (2026). Women with Parkinson's disease may show more Alzheimer's-related brain changes than men. https://medicalxpress.com/news/2026-06-women-parkinson-disease-alzheimer-brain.html
2. Sex-Specific Associations of α-Synuclein Pathology With Tau Accumulation. JAMA Network. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2816007
3. Iman Beheshti, Samuel Booth, Ji Hyun Ko (2024). Differences in brain aging between sexes in Parkinson’s disease. npj Parkinson's Disease. https://doi.org/10.1038/s41531-024-00646-w
4. Javier Oltra, Carme Uribe, Anna Campabadal, et al. (2022). Sex Differences in Brain and Cognition in de novo Parkinson's Disease. Frontiers in Aging Neuroscience. https://doi.org/10.3389/fnagi.2021.791532
5. Yasuaki Mizutani, Reiko Ohdake, Harutsugu Tatebe, et al. (2023). Associations of Alzheimer's-related plasma biomarkers with cognitive decline in Parkinson's disease. Journal of Neurology. https://doi.org/10.1007/s00415-023-11875-z
6. Hui Li, Chen Zhang, Xiuqin Jia, Qi Yang. Sex differences in brain structure in de novo Parkinson’s disease: A cross-sectional and longitudinal neuroimaging study. ISMRM Annual Meeting. https://doi.org/10.58530/2023/3202