HNF1A and HNF1B, which are associated with MODY3 and MODY5, respectively, act together with HNF4A in an autoregulatory circuit in an overlapping set of tissues, with HNF4A proposed to be the most upstream regulator of this circuit (Boj et al., 2001; Nagaki and Moriwaki, 2008). Here, HNF4A is linked to maturity-onset diabetes of the young type 3.