Abstract

Abstract Introduction Synaptic dysfunction is an early event in Alzheimer's disease (AD) pathogenesis and directly related to cognitive impairment. Consequently, synaptic biomarkers may be valuable tools for both early diagnosis and disease stage. Neurogranin (Ng) is a postsynaptic protein involved in memory consolidation. Methods We developed three monoclonal anti‐Ng antibodies. Mass spectrometry and a novel enzyme‐linked immunosorbent assay were used to analyze cerebrospinal fluid (CSF) Ng in three independent clinical cohorts including patients with AD dementia (n = 100 in total), mild cognitive impairment patients (MCI), (n = 40) and controls (n = 80 in total). Results We show in three independent clinical cohorts a marked increase in CSF Ng levels in AD dementia ( P < .001 in all studies). In addition, high CSF Ng levels at the MCI stage predicted progression to dementia due to AD with a hazard ratio of 12.8 (95% confidence interval 1.6–103.0, P = .02). In amyloid‐positive MCI patients, high CSF Ng correlated with a more rapid change in cognition during clinical follow‐up ( P = .03). Discussion These results suggest that CSF Ng is a novel AD biomarker that may be used to monitor synaptic degeneration, and correlates with the rate of cognitive decline in prodromal AD.