Alterations in the genes ABCC8, KCNJ11, and GCK can result in phenotypes at opposite ends of the glycemic control spectrum (hypoglycemia or hyperglycemia), or alternatively a phenotype corresponding to the middle of the spectrum, resulting in maturity onset diabetes of the young (MODY), transient neonatal diabetes, or diabetes mellitus type II. The gene discussed is GCK; the disease is Hypoglycemia.