As described in the current study, analyses of skin tumor promotion susceptibility using interval specific subcongenic mouse strains indicate that Psl1 is a compound locus made up of a cluster of subloci (see Figure 1), similar to other QTL affecting complex traits such as blood pressure (reviewed in Rapp and Joe 2012), diabetes (Granhall et al. 2006), body composition (Diament and Warden 2004; Farber and Medrano 2007; Ishikawa et al. 2007; Prevorsek et al. 2010), and cancer (Samuelson et al. 2005, 2007). Here, SPPL2B is linked to diabetes mellitus.