PSEN1 and Alzheimer disease: New approaches seek to incorporate LOAD risk-factor genes in tandem with FAD mutations, other risk alleles, and environmental variables to begin understand the complex age-dependent etiology of AD that has remained elusive to date (Onos et al., 2016; Castillo et al., 2017; Pandey et al., 2019; Preuss et al., 2019; Oblak et al., 2020).