Only a very small number of above-threshold GWAS loci, including SORT1 for LDL cholesterol, the FTO/IRX3 locus for obesity, and the SCN5A/SCN10A locus for QRS duration, have been investigated in detail (Musunuru et al., 2010; van den Boogaard et al., 2012; van den Boogaard et al., 2014; Arnolds et al., 2012; Smemo et al., 2014). The gene discussed is IRX3; the disease is obesity due to melanocortin 4 receptor deficiency.