PRKN and Parkinson disease: In Drosophila, NAM treatment improved climbing ability in α-synuclein transgenic flies,35 whereas in mice, NAM could rescue the MPTP-induced dopaminergic neuronal loss in the substantia nigra pars compacta.36 The present study extends these observations in a PARKIN model of PD by showing that the enhancement of NAD+ metabolism has a direct impact on mitochondrial function.