The HNF4A gene is transcribed from either of two promoters, P1 and P2, the resulting mRNA is translated, and the protein products localize in the nucleoplasm. Transcription is positively regulated by HNF1A. Many of the molecular details of these events have not been studied experimentally in humans, but are inferred from mouse model systems (Boj et al. 2001). Transcription in mouse and human pancreatic beta cells is P2-dependent and in humans yields three isoforms of mature HNF4A protein. A point mutation in the human P2 genomic DNA sequence is associated with MODY (maturity onset diabetes of the young), consistent with the hypothesis that P2-mediated transcription is essential for HNF4A expression and normal beta cell function (Hansen et al. 2002).