HNF1A and maturity-onset diabetes of the young type 3: Not surprisingly, patients with MODY3 show a highly heterogeneous clinical phenotype influenced by type and position of HNF1α mutation (Bellanne-Chantelot et al., 2008), patient genetic background (Lango Allen et al., 2010), and environmental effects both before and after birth (Hattersley, 1998; Stride et al., 2002).