Alpha-synuclein co-pathology in a real-world early Alzheimer's disease cohort.

BACKGROUND

Most Alzheimer's disease (AD) cases show mixed pathology, with α-synuclein (αSyn) aggregates present in a substantial proportion. The cerebrospinal fluid (CSF) α-synuclein seed amplification assay (αS-SAA) enables in vivo detection of pathogenic αSyn aggregates, but its clinical significance remains unclear.

METHODS

We prospectively evaluated 108 individuals with mild cognitive impairment or mild dementia due to suspected AD undergoing lumbar puncture for anti-amyloid therapy (ATT) eligibility. CSF AD biomarkers and αS-SAA were analyzed alongside cognitive, olfactory, and rapid eye movement sleep behavior disorder (RBD) assessments.

RESULTS

Of 65 participants with biomarker-confirmed AD, 21 (32.3%) were αS-SAA positive. Positivity was linked to older age at testing and self-reported olfactory impairment (P = 0.004), but not other demographic or cognitive features. Within the αS-SAA-positive group, RBD presence correlated with faster seeding kinetics.

CONCLUSIONS

αS-SAA positivity is common in early AD and associated with olfactory dysfunction. Longitudinal follow-up is required to test if assay status predicts response to ATTs.