VMAT2 LO mice, a PD animal model lacking VMAT2, the monoamine transporter that we found to be reduced in the striatum of 12-month-old c-rel–/– mice (Parrella et al., 2019), show an age-dependent apathetic behavior in the nest building test similar to that observed in our study (Baumann et al., 2016). This evidence concerns the gene REL and Parkinson disease.