, something that hasn’t previously been extensively investigated in longitudinal studies.
By analyzing cerebral spinal fluid (CSF), as well as cognitive and brain imaging assessments conducted every few years for two decades, researchers were able to plot the course of changing levels of amyloid-beta 42 (Abeta42), phosphorylated tau 181 (p-tau181), and neurofilament light chain (NfL) in adults with Alzheimer’s disease and mark when those levels began to deviate from those of adults without Alzheimer’s disease.
Levels of Abeta42 in CSF and the ratio of Abeta42 to Abeta40 in people who developed Alzheimer’s disease diverged from those of peers who remained cognitively normal at 18 years and 14 years, respectively, before clinical signs of disease appeared.
The level of p-tau181 in CSF increased 11 years before disease onset, and NfL levels, a measure of neurodegeneration, increased 9 years before diagnosis.
These changes were followed by hippocampal atrophy and cognitive decline a few years later.
The results also show “an apparent accelerated change in concentrations of CSF biomarkers followed by a slowing of this change up to the time of diagnosis,” report the authors, led by Jianping Jia, MD, PhD, with the Innovation Center for Neurological Disorders, Xuanwu Hospital, Capital Medical University, Beijing, China.
The study was published online in The New England Journal of Medicine.
Time Course of Biomarker Changes
Dr. Jia and colleagues conducted a nested case-control study within the China Cognition and Aging Study (COAST). They matched 648 adults who developed Alzheimer’s disease to 648 who remained cognitively normal. CSF, cognitive, and brain imaging assessments were performed every 2-3 years for a median of about 20 years.
Within both groups, men slightly outnumbered women. At baseline, CSF biomarker levels, cognitive scores, and hippocampal volumes were similar in the two groups. Adults who developed Alzheimer’s disease were more likely than their matched controls to be carriers of the APOE epsilon-4 allele (37% vs 20%).
In terms of CSF Abeta42, the level of this biomarker in those who developed Alzheimer’s disease diverged from the level in controls an estimated 18 years before clinical diagnosis. At that time, the level was lower by a mean 59.13 pg/mL in the Alzheimer’s disease group.
A difference in the ratio of CSF Abeta42 to Abeta40 between the two groups appeared an estimated 14 years before the diagnosis of Alzheimer’s disease (difference in mean values, −0.01 pg/mL).
Differences between the two groups in CSF p-tau181 and total tau concentrations were apparent roughly 11 and 10 years before diagnosis, respectively. At those times, the mean differences in p-tau181 and total tau concentrations were 7.10 pg/mL and 87.10 pg/mL, respectively.
In terms of NfL, a difference between the groups was observed 9 years before diagnosis, with its trajectory progressively deviating from the concentrations observed in cognitively normal groups at that time, to a final mean difference in NfL of 228.29 pg/mL.
Bilateral hippocampal volume decreased with age in both groups. However, the decrease began to differ between the two groups 8 years before Alzheimer’s disease diagnosis, at which time volume was lower by 358.94 mm3 in the Alzheimer’s disease group compared with the control group.
Average Clinical Dementia Rating–Sum of Boxes (CDR-SB) scores in the Alzheimer’s disease group began to worsen compared with the control group at about 6 years before diagnosis.
As Alzheimer’s disease progressed, changes in CSF biomarkers increased before reaching a plateau.