Mutant Arx loss-of-function mice present with severe hypoglycemia, dehydration, and death within the first few days of life; a close look into their pancreas shows that the glucagon-producing alpha-cell population is practically non-existent, with a marked increase in beta- and delta-cell populations, serving as evidence to ARX’s role in defining the fate of endocrine cells. This evidence concerns the gene ARX and Hypoglycemia.