Balanced Reelin and FMRP activity stabilize the network, whereas deficiencies in either—compounded by Aβ, tau, or ApoE4—produce hypoplastic (Liu et al., 2001) or hyperdepressed synaptic states characteristic of ASD, FXS, and AD (Bleuzé et al., 2021). The gene discussed is MAPT; the disease is fragile X syndrome.