It has also been shown recently that accumulation of nicotinamide mononucleotide (NMN), the substrate for Nmnat isoforms (and WldS enzymic activity), may be a toxic agent that precipitates axonal fragmentation at the onset of WD, following a steep decline in axonal Nmnat-2 levels (Gilley and Coleman, 2010; Gilley et al., 2013; Milde et al., 2013; Conforti et al., 2014; Di Stefano et al., 2014). Here, NMNAT1 is linked to Wilson disease.