NPTX2 and Alzheimer disease: BDNF decorrelated at the transcript layer (r = 0.69 → 0.54), while the RNA–protein correlation remained stable at 0.36 in both groups; separation increased from D = 0.72 in RNA to D = 0.97 in RNA–MS, moving from moderate to moderate-to-strong and consistent with lower BDNF RNA together with lower NPTX2 protein in AD (Fig. 3L and 3M).