MBI‐apathy, ApoEɛ2, and risk for Alzheimer disease dementia

AbstractBackgroundApathy, characterized by decreased interest, initiative, and emotional reactivity, is amongst the most common neuropsychiatric symptoms in dementia. However, apathy can emerge before dementia and constitutes a domain of mild behavioral impairment (MBI), an at‐risk state for incident cognitive decline and dementia. MBI‐apathy is the de novo emergence of persistent apathy in dementia‐free older adults and may be a driving factor in dementia risk conferred by MBI. Apolipoprotein E (ApoE) is a risk marker for Alzheimer disease (AD) dementia. Compared to ApoEɛ3 homozygotes, ApoEɛ2 carriers are 40% less likely to develop AD while ApoEɛ4 carriers are 3.2‐14.9 times more likely. We investigated the association between MBI‐apathy, ApoE, and incident dementia. We hypothesized that ɛ2 would have protective effects for MBI‐apathy associated risk, compared to ɛ3 and ɛ4.MethodDementia‐free participants in the National Alzheimer’s Coordinating Centre were stratified as MBI‐apathy and no‐NPS until dementia diagnosis, based on Neuropsychiatric Inventory Questionnaire scores at 2 consecutive visits. ApoE genotypes were categorized by ɛ2 (ɛ2/ɛ2, ɛ2/ɛ3), ɛ3 (ɛ3/ɛ3), and ɛ4 (ɛ4/ɛ3, ɛ4/ɛ4) alleles. Group characteristics were contrasted to determine covariate inclusion in regression modelling. Cox regressions assessed risk of incident dementia and included an interaction term for MBI‐apathy and ApoE allele.ResultsOf the 3,644 participants (3,022 Normal‐Cognition); 314 had MBI‐apathy (Table 1). Significant main effects were found for MBI‐apathy and incident dementia (HR:2.51, 95% CI:1.99‐3.17, p<0.001) as well as interaction effects with ApoE. In MBI‐apathy (ɛ3 as reference), the ɛ2 group had a 60% lower dementia risk (adjusted HR:0.40, 95% CI:0.19‐0.85) while ɛ4 had a 16% higher risk (adjusted HR:1.16, 95% CI:0.80‐1.69) (Figure 1). Of the 125 participants with apathy who progressed to dementia, 80.8% had AD. In the no‐NPS group (ɛ3 as reference), ɛ2 individuals had a 17% lower dementia risk (adjusted HR:0.83, 95% CI:0.52‐1.33) while ɛ4 individuals had a 177% higher risk (adjusted HR:2.77, 95% CI:2.13‐3.59) (Figure 2).ConclusionTo our knowledge, this is the first study examining the relationship between MBI‐apathy and ApoE status in determining dementia risk. Results suggest that ApoE modifies the association between MBI‐apathy and incident dementia with the ɛ2 allele acting as a protective factor.