MTAP and nevus: The usefulness of nevus counts as an intermediate phenotype to melanoma has already been shown in genome-wide association studies (GWAS), as common single nucleotide polymorphisms (SNPs) in the loci PLA2G6 and MTAP were first associated with total body nevus count (Falchi et al., 2009, Nan et al., 2011) and then subsequently with melanoma risk (Barrett et al., 2011, Bishop et al., 2009).