Recent proteomics studies of Alzheimer’s disease (AD) brains have identified a core set of proteins, including MDK, PTN, NTN1, NTN3, and SFRP1, that share several characteristics: (i) a high correlation with Aβ throughout AD progression; (ii) a prominent presence in the aggregated proteome; and (iii) enrichment in amyloid plaques16,19. The gene discussed is PTN; the disease is Alzheimer disease.