**Core Concept**
Prader-Willi syndrome (PWS) is a genetic disorder characterized by a deletion or inactivation of the paternal copy of chromosome 15. This results in a deficiency of several hormones, including growth hormone, and an imbalance of various neurotransmitters. The clinical manifestations of PWS include hypotonia, failure to thrive, and hyperphagia leading to obesity.

**Why the Correct Answer is Right**
The correct answer is related to the hormone levels that are increased in PWS. In PWS, there is an increase in the levels of **neuropeptide Y (NPY)**, which is a potent stimulator of appetite. This increase in NPY is thought to contribute to the hyperphagia and obesity seen in PWS patients. Additionally, there is also an increase in **ghrelin**, a hormone that stimulates appetite and food intake.

**Why Each Wrong Option is Incorrect**
**Option A:** Growth hormone levels are actually decreased in PWS, not increased.
**Option B:** Insulin levels may be elevated in PWS due to insulin resistance, but this is not the correct answer.
**Option C:** Thyroid-stimulating hormone (TSH) levels may be normal or decreased in PWS, but this is not the correct answer.

**Clinical Pearl / High-Yield Fact**
PWS patients often have a characteristic "cowlick" or "duck bill" appearance of the upper lip, and may also have a small, narrow palate.

**Correct Answer:** .