SLC12A2 and Alzheimer disease: In AD, however, pathological alterations in the excitatory–inhibitory (E/I) balance have been documented, most notably the downregulation of KCC2 in hippocampal and prefrontal circuits, together with the aberrant upregulation of NKCC1, which is normally suppressed in mature neurons (Kreis et al., 2021; Lam et al., 2022; Del Turco et al., 2023; Lam et al., 2023; Barbour et al., 2024).