**Core Concept**
Obesity is often linked to alterations in appetite-regulating hormones, particularly ghrelin, which is involved in the stimulation of appetite. Normally, obese individuals exhibit decreased ghrelin levels, whereas individuals with normal weight have elevated ghrelin levels.

**Why the Correct Answer is Right**
In Prader-Willi syndrome, a rare genetic disorder characterized by severe infantile hypotonia, feeding difficulties, and obesity, patients exhibit increased ghrelin levels despite their obesity. This anomaly is thought to be related to the complex interplay between ghrelin, leptin, and other appetite-regulating hormones in this syndrome. The increased ghrelin levels in Prader-Willi syndrome may be a contributing factor to the excessive appetite and food-seeking behavior seen in these patients.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because there is no established link between obesity and high ghrelin levels in Cushing's syndrome, a condition characterized by excess cortisol production.
**Option B:** This option is incorrect because Prader-Willi syndrome is a specific condition where high ghrelin levels are observed in the context of obesity, rather than a general characteristic of all obese individuals.
**Option C:** This option is incorrect because Prader-Willi syndrome is not associated with decreased ghrelin levels; instead, it is characterized by increased ghrelin levels.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize that Prader-Willi syndrome can present with a complex array of symptoms, including obesity, hyperphagia, and developmental delay, and that high ghrelin levels may be a distinguishing feature of this condition.

**Correct Answer:** D.