The possible explanation is that Alzheimer’s disease is highly heterogeneous and fish oil supplements may interact with apolipoprotein E (APOE) genotype and stage of Alzheimer’s disease pathologic changes (Gatz et al., 2006; Ridge et al., 2016; Arellanes et al., 2020; Scheltens et al., 2021). Here, APOE is linked to early-onset autosomal dominant Alzheimer disease.