SNCA and Parkinson disease: Our current results extend previous studies from our group and others showing that neurogenesis is reduced in the olfactory bulb and the hippocampus of adult α-synuclein transgenic mice by diminished survival of neuronal precursors [14] and, importantly, that the neurogenic system is compromised in human PD brains, where proliferation of neural progenitor cells is decreased in the hippocampus and SVZ [28].