Prognostic value of amyloid/tau/neurodegeneration (ATN) classification based on diagnostic cerebrospinal fluid samples for Alzheimer's disease

Abstract

Objective: The primary study objective of this retrospective academic memory clinic-based observational longitudinal study was to investigate the prognostic value of a cerebrospinal fluid (CSF)-based ATN classification for subsequent cognitive decline during the 3 years following lumbar puncture in a clinical, real-life setting. The secondary objective was to investigate the prognostic value of CSF biomarkers as continuous variables.

Methods: Data from 228 patients (median age 67 (47-85) years), who presented at the Neurology Memory Clinic UZ/KU Leuven between September 2011 and December 2016, were included with a follow-up period of up to 36 months. Patients underwent a CSF AD biomarker test for amyloid-beta 1-42 (Aβ₄₂)_, hyperphosphorylated tau (p₁₈₁-tau) and total tau (t-tau) in the clinical work-up for diagnostic reasons. Patients were divided into ATN classes based on CSF biomarkers: Aβ₄₂ for amyloid (A), p₁₈₁-tau for tau (T), and t-tau as a measure for neurodegeneration (N). Based on retrospective data analysis, cognitive performance was evaluated by Mini Mental State Examination (MMSE) scores every 6 months over a period up to 36 months following the lumbar puncture. The statistical analysis was based on linear mixed-effects modeling (LME).

Results: The distribution in the current clinical sample was as follows: A-/T-/N- 32.02%, A+/T-/N- 33.33%, A+/T+/N+ 17.11%, A+/T-/N+ 11.84%, A-/T-/N+ 4.39%, A-/T+/N+ 1.32% (3 cases), with no cases in the A-/T+/N- and A+/T+/N- class. Hence, the latter 3 classes were excluded from further analyses. The change of MMSE relative to A-/T-/N- over a 36-month period was significant in all four ATN classes: A+/T+/N+ = - 4.78 points on the MMSE; A-/T-/N+ = - 4.76; A+/T-/N+ = - 2.83; A+/T-/N- = - 1.96. The earliest significant difference was seen in the A+/T+/N+ class at 12 months after baseline. The effect of ATN class on future cognitive decline was confirmed for a different set of CSF thresholds. All individual baseline CSF biomarkers including the Aβ₄₂/t-tau ratio showed a significant correlation with subsequent cognitive decline, with the highest correlation seen for Aβ₄₂/t-tau.

Conclusion: ATN classification based on CSF biomarkers has a statistically significant and clinically relevant prognostic value for the course of cognitive decline in a 3-year period in a clinical practice setting.

Keywords: ATN classification; Alzheimer’s disease; Biomarkers.