Our finding that even partial downregulation of HNF4α either in cultured hepatocytes after siRNA-mediated Hnf4α knockdown (Fig. 4b) or in vivo in heterozygous Hnf4a knockout mice (Fig. 5c) still leads to a statistically significant proportional decrease in Agxt2 expression suggests that the effect of HNF4a on Agxt2 transcription is dose-dependent, which makes our study relevant to the large number of patients with mild HNF4α deficiency. Here, HNF4A is linked to hyperinsulinemic hypoglycemia, familial, 4.