APP and Alzheimer disease: However, postmortem analyses of AD patients' tissues have shown a decline in Olig2+ cells (Behrendt et al. 2013), and a reduction in OPC density has been observed in the APP/PS1 (Chacon‐De‐La‐Rocha et al. 2020) and 5xFAD model (Zota et al. 2024).