Signaling of IGF-I, IGF-II, and neurotrophin are more impaired in DLB than PD, corresponding with DLB’s more pronounced neurodegeneration, oxidative stress, and alpha-synuclein accumulation, causing PD/DLB associated abnormalities in central nervous system neurons, and therefore may contribute to their molecular pathogenesis. Here, IGF2 is linked to Parkinson disease.