**Core Concept**
Cushing's disease is a form of Cushing's syndrome caused by an ACTH-producing pituitary adenoma, leading to excess cortisol production. This results from an abnormality in the hypothalamic-pituitary-adrenal (HPA) axis, specifically at the level of the pituitary gland.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of Cushing's disease, which involves an overproduction of adrenocorticotropic hormone (ACTH) by a pituitary adenoma. ACTH stimulates the adrenal glands to produce excessive amounts of cortisol. This leads to a range of symptoms, including weight gain, hypertension, and glucose intolerance. The HPA axis is regulated by a balance between corticotropin-releasing hormone (CRH) from the hypothalamus and ACTH from the pituitary gland, which in turn stimulates cortisol production from the adrenal glands.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Cushing's disease is specifically caused by a pituitary adenoma, whereas primary adrenal causes (e.g., adrenal tumors) are classified as Cushing's syndrome due to adrenal disease.

**Option B:** This option is incorrect because Cushing's disease is not typically associated with an excess of aldosterone, which is a different mineralocorticoid produced by the adrenal glands.

**Option C:** This option is incorrect because Cushing's disease is not typically caused by a deficiency of cortisol, but rather an excess.

**Clinical Pearl / High-Yield Fact**
A classic clinical feature of Cushing's disease is **buffalo hump** formation, a fatty deposit that develops on the upper back due to excess cortisol production.

**Correct Answer:** D.