HNF1B and type 2 diabetes mellitus: Variation in the P2 promoter of HNF4A, presumably leading to a decrease in HNF4A expression, has been associated with an increased risk of developing Type 2 diabetes (Weedon et al. 2004), whilst bi-allelic inactivation of HNF1A and HNF1B has been shown to cause a number of types of cancer (Bluteau et al. 2002; Terasawa et al. 2004; Rebouissou et al. 2005).