For example, several GWAS loci for type 2 diabetes contain genes known to harbour causal coding variants for rare Mendelian syndromes related to type 2 diabetes (e.g. HNF1A, HNF1B, WFS1, PPARG, KCNJ11, HNF4A, GCK). Here, HNF4A is linked to type 2 diabetes mellitus.