As another example still needing further investigation, preclinical in vitro studies introducing microglia that are homozygous for the nonpathogenic apolipoprotein E ε3 allele into tissues carrying the apolipoprotein E ε4 (a risk allele for Alzheimer's disease) report that the tissues display less β‐amyloid1‐42 accumulation (Lin et al. 2018). This evidence concerns the gene APOE and Alzheimer disease.