Lastly, several nervous system pathways were underrepresented in the differentially expressed geneset from old mice compared with young mice, including the neuroprotective role of THOP1 (Thimet Oligopeptidase 1) in Alzheimer’s disease (p = 1.15E−02; z = − 3.153), neurotrophin/TRK (neurotrophic receptor tyrosine kinase 1) signaling (p = 1.26–02; z = − 2.887), and the Wnt/Ca+ signaling (p = 4.79E−03; z = − 2.673) pathways that contribute to neuron protection and regeneration. The gene discussed is NTRK1; the disease is Alzheimer disease.