A 43-year-old male high-level executive presents to his physician due to a persistent dizziness when standing quickly. He also has been exhibiting chronic fatigue, some muscle weakness, and an unusual craving for salty foods. The physician notices that the patient has a constant "bronze tan," and blood obtained during the visit demonstrated not only normal cholesterol levels but also hypoglycemia, hyperkalemia, and hyponatremia. The underlying cause for these problems is which one of the following?