Some further studies also describe different monoaminergic dysfunctions on the VMAT2 hypomorphic mice model, such as the exhibition of progressive noradrenergic neurodegeneration in the locus ceruleus as it preceded degeneration of the substantia nigra pars compacta (Taylor et al., 2014), the disruption of serotonin signaling without degeneration of serotonin neurons (Alter et al., 2016), and especially the general loss of monoamines with some of the non-motor symptoms associated with PD (Taylor et al., 2009). Here, SLC18A2 is linked to Parkinson disease.