ABSTRACT
INTRODUCTION: Subjective cognitive decline (SCD) has been proposed as a potential preclinical stage of Alzheimer's disease (AD). Nevertheless, the genetic and biomarker profiles of SCD individuals remain mostly unexplored. METHODS: We evaluated apolipoprotein E (APOE) ε4's effect in the risk of presenting SCD, using the Fundacio ACE Healthy Brain Initiative (FACEHBI) SCD cohort and Spanish controls, and performed a meta-analysis addressing the same question. We assessed the relationship between APOE dosage and brain amyloid burden in the FACEHBI SCD and Alzheimer's Disease Neuroimaging Initiative cohorts. RESULTS: Analysis of the FACEHBI cohort and the meta-analysis demonstrated SCD individuals presented higher allelic frequencies of APOE ε4 with respect to controls. APOE dosage explained 9% (FACEHBI cohort) and 11% (FACEHBI and Alzheimer's Disease Neuroimaging Initiative cohorts) of the variance of cerebral amyloid levels. DISCUSSION: The FACEHBI sample presents APOE ε4 enrichment, suggesting that a pool of AD patients is nested in our sample. Cerebral amyloid levels are partially explained by the APOE allele dosage, suggesting that other genetic or epigenetic factors are involved in this AD endophenotype.
Subject(s)
Alzheimer Disease/genetics , Amyloid/blood , Apolipoprotein E4/genetics , Cognitive Dysfunction/genetics , Diagnostic Self Evaluation , Alleles , Biomarkers/metabolism , Brain/diagnostic imaging , Brain/metabolism , Cognitive Dysfunction/diagnostic imaging , Cross-Sectional Studies , Female , Genotype , Humans , Male , Meta-Analysis as Topic , Middle Aged , Neuroimaging/methods , Risk Factors , SpainABSTRACT
OBJECTIVE: To investigate CSF markers involved in amyloid precursor protein processing, neuronal damage, and neuroinflammation in the preclinical stages of Alzheimer disease (AD) and participants with suspected non-Alzheimer pathology (SNAP). METHODS: We collected CSF from 266 cognitively normal volunteers participating in a cross-sectional multicenter study (the SIGNAL study) to investigate markers involved in amyloid precursor protein processing (Aß42, sAPPß, ß-secretase activity), neuronal damage (total-tau [t-tau], phospho-tau [p-tau]), and neuroinflammation (YKL-40). We analyzed the relationship among biomarkers, clinical variables, and the APOE genotype, and compared biomarker levels across the preclinical stages of the National Institute on Aging-Alzheimer's Association classification: stage 0, 1, 2, 3, and SNAP. RESULTS: The median age in the whole cohort was 58.8 years (range 39.8-81.6). Participants in stages 2-3 and SNAP had higher levels of YKL-40 than those in stages 0 and 1. Participants with SNAP had higher levels of sAPPß than participants in stage 0 and 1. No differences were found between stages 0, 1, and 2-3 in sAPPß and ß-secretase activity in CSF. Age correlated with t-tau, p-tau, and YKL-40. It also correlated with Aß42, but only in APOE ε4 carriers. Aß42 correlated positively with t-tau, sAPPß, and YKL-40 in participants with normal Aß42. CONCLUSIONS: Our findings suggest that inflammation in the CNS increases in normal aging and is intimately related to markers of neurodegeneration in the preclinical stages of AD and SNAP. sAPPß and ß-secretase activity are not useful diagnostic or staging markers in preclinical AD.
