HNF4A and type 2 diabetes mellitus: As a pivotal transcription factor in the progress and functions of the pancreatic β-cells, hepatocyte nuclear factor 4α (HNF-4α) is differentially expressed in many tissues including the liver and pancreas [5]. HNF-4α spans 29 kb on chromosome 20q13.1-13.2 [6], which is a known T2D susceptibility locus. HNF-4α was shown to play a significant role in the development of maturity-onset diabetes of the young-1, which is characterized by impaired insulin secretion [7].