Furthermore, with the use of the CRISPR/Cas9 system, iPSCs with the APOE ε4 allele were converted to the APOE ε3 allele and this consequently caused a reduction in AD pathology (Lin et al., 2018), suggesting that the role of APOE as a risk factor for AD might be triggered by microglia. The gene discussed is APOE; the disease is Alzheimer disease.