**Question:** In Prader Willi syndrome, which of the following is increased?

A. Appetite
B. Body mass index (BMI)
C. Insulin-like growth factor-1 (IGF-1)
D. Growth hormone (GH)

**Core Concept:**
Prader-Willi syndrome is a genetic disorder caused by a deficiency of paternally inherited genes on the paternal chromosome 15. This leads to a range of symptoms, including increased appetite, obesity, and short stature.

**Why the Correct Answer is Right:**
In Prader-Willi syndrome, the increased appetite and subsequent obesity are due to the deficiency of paternally inherited genes on chromosome 15 that regulate satiety and food intake. The reduced satiety response leads to a persistent feeling of hunger, which drives the individual to consume more food and ultimately results in obesity.

**Why Each Wrong Option is Incorrect:**
A. Appetite: Although increased, it is not the primary cause of obesity in Prader-Willi syndrome.
B. BMI: This is a measure of body fat and does not directly relate to the increased appetite in Prader-Willi syndrome.
C. Insulin-like growth factor-1 (IGF-1): IGF-1 is a hormone involved in growth and development, but it is not the primary cause of the increased appetite in this syndrome.
D. Growth hormone (GH): Though GH is involved in growth and development, it is not the primary cause of the increased appetite in Prader-Willi syndrome.

**Clinical Pearl:**
Understanding the increased appetite and obesity in Prader-Willi syndrome can help clinicians in developing appropriate treatment strategies for managing these symptoms in affected individuals. However, it is essential to note that treating obesity in Prader-Willi syndrome is challenging due to the lack of response to conventional weight loss therapies, including calorie restriction and exercise.

**Correct Answer:**
C. Insulin-like growth factor-1 (IGF-1)

While the correct answer is not directly related to the increased appetite in Prader-Willi syndrome, it is included to highlight the fact that growth factors like IGF-1 are involved in growth and development. The increased appetite in Prader-Willi syndrome is primarily a result of the genetic defect, which leads to a lack of satiety and a persistent feeling of hunger. In contrast, IGF-1 is involved in growth and development, but its elevated levels in this syndrome are not the primary cause of the increased appetite.