AQP4, the master regulator of the water channel, tightly controls water fluxes into and out of the cell.[45] Increased AQP4 expression leading to excessive water influx is implicated in astrocyte swelling in pathological conditions such as cerebral edema and traumatic brain injury.[57, 58, 59] Thus, peripheral nerve injury may activate NFAT5‐AQP4 signaling, culminating in astrocyte swelling in the SDH. The gene discussed is AQP4; the disease is injury.