PRNP and concussion: In chronic mTBI, there were elevated CD81-normalized NDE levels of usually neuropathologic β-amyloid peptide 1–42 (Aβ42), 1.6-fold (P < 0.0001 relative to controls); XIIIa, 1.3-fold (P = 0.042); P-T181-tau, 2.2-fold (P < 0.0001); P-S396-tau, 1.6-fold (P < 0.01); IL-6, 16-fold (P < 0.0001); and prion cellular protein (PRPc), 5.1-fold (P < 0.0001), with lesser or greater (XIIIa, IL-6, PRPc) increases in acute mTBI.