Mild behavioral impairment: measurement and clinical correlates of a novel marker of preclinical Alzheimer’s disease

Background Late-life onset neuropsychiatric symptoms are established risk factors for dementia. The mild behavioral impairment (MBI) diagnostic framework was designed to standardize assessment to determine dementia risk better. In this Mini Review, we summarize the emerging clinical and biomarker evidence, which suggests that for some, MBI is a marker of preclinical Alzheimer’s disease. Main MBI is generally more common in those with greater cognitive impairment. In community and clinical samples, frequency is around 10–15%. Mounting evidence in cognitively normal samples links MBI symptoms with known AD biomarkers for amyloid, tau, and neurodegeneration, as well as AD risk genes. Clinical studies have found detectable differences in cognition associated with MBI in cognitively unimpaired people. Conclusion The emerging evidence from biomarker and clinical studies suggests MBI can be an early manifestation of underlying neurodegenerative disease. Future research must now further validate MBI to improve identification of those at the very earliest stages of disease.

Vascular risk burden is a key player in the early progression of Alzheimer's disease

Understanding whether vascular risk factors synergistically potentiate Alzheimer's disease progression is important in the context of emerging treatments for preclinical Alzheimer's disease. The existence of a synergistic relationship could suggest that the combination of therapies targeting Alzheimer's disease pathophysiology and vascular risk factors might potentiate treatment outcomes. In the present retrospective cohort study, we tested whether vascular risk factor burden interacts with Alzheimer's disease pathophysiology to accelerate neurodegeneration and cognitive decline in cognitively unimpaired subjects. We evaluated 503 cognitively unimpaired participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI) study. Baseline vascular risk factor burden was calculated considering the history of cardiovascular disease, hypertension, diabetes mellitus, hyperlipidemia, stroke or transient ischemic attack, smoking, atrial fibrillation, and left ventricular hypertrophy. Alzheimer's disease pathophysiology was evaluated using cerebrospinal fluid (CSF) amyloid-β1-42 (Aβ1-42) reflecting brain amyloidosis (A) and tau phosphorylated at threonine 181 (p-tau181) reflecting brain tau pathology (T). Individuals were dichotomized as having an elevated vascular risk factor burden (V+ if having two or more vascular risk factors) and as presenting preclinical Alzheimer's disease [(AT)+ if having abnormal CSF p-tau181 and Aβ1-42 levels]. Neurodegeneration was assessed with plasma neurofilament light (NfL) and global cognition with the modified version of the Preclinical Alzheimer's Cognitive Composite. Linear mixed-effects models revealed that an elevated vascular risk factor burden synergistically interacted with Alzheimer's disease pathophysiology to drive longitudinal increases in plasma NfL levels (β = 5.08, P = 0.016) and cognitive decline (β = -0.43, P = 0.020). Additionally, we observed that vascular risk factor burden was not associated with CSF Aβ1-42 or p-tau181 changes over time. Survival analysis demonstrated that individuals with preclinical Alzheimer's disease and elevated vascular risk factor burden [(AT)+V+] had a significantly greater risk of clinical progression to cognitive impairment (adjusted Hazard Ratio = 3.5, P < 0.001). Our results support the notion that vascular risk factor burden and Alzheimer's disease pathophysiology are independent processes; however, they synergistically lead to neurodegeneration and cognitive decline. These findings can help in providing the blueprints for the combination of vascular risk factor management and Alzheimer's disease pathophysiology treatment in preclinical stages. Moreover, we observed plasma NfL as a robust marker of disease progression that may be used to track therapeutic response in future trials.