Invariable expression of tropomyosin-related kinase A (TrkA) and sortilin (Additional file 1: Fig. S6), the co-receptors of p75NTR for cell survival and death respectively, suggest their insignificant role in prion disease, so also with proNGF/NGF, the genuine ligand of p75NTR [132]. The gene discussed is NGF; the disease is prion disease.