APP and Down syndrome: Interestingly, examination of the α1–3 and γ2 subunits revealed the α1, α3, and γ2 subunits to have considerably altered expression profiles in growing Down syndrome hippocampi, with the α3 subunit being most impacted; specifically, all fetal hippocampus subfields and developmental periods showed a preferential downregulation of α3 subunits, an effect linked to higher levels of amyloid precursor protein in the hippocampus (Milenkovic et al., 2018).