This is evidenced by recent results obtained from fluorescent in situ hybridization (FISH)in individual neurons of AD patients’ brain (Yurov et al., 2023),as well as experimental studies on mice with knockdown ofone allele of the BMI1 gene (encodes a protein of the Polycombgroup and regulates compaction of heterochromatin).In adults, BMI1 is normally expressed ubiquitously in brainneurons, but is reduced in AD. The gene discussed is BMI1; the disease is Alzheimer disease.