Three genetic forms of AD have been proposed; autosomal dominant AD (ADAD) (Bateman et al., 2012), Down syndrome associated AD (DSAD) (Fortea et al., 2020, 2021), and more recently, apolipoprotein E epsilon 4 (APOE4) homozygosity (Fortea et al., 2024). This evidence concerns the gene APOE and Alzheimer disease.