The ITT is performed under supervision by intravenous injection of 0.15 units/kg (0.1 units/kg if high suspicion of hypocortisolism, 0.2units/kg in insulin resistant states such as diabetes mellitus or acromegaly) soluble insulin with measurement of plasma cortisol at 0, 30, 45, 60, 90 and 120 min. The gene discussed is INS; the disease is adrenocortical insufficiency.