## **Core Concept**
The question describes a child with a unique set of physical and behavioral characteristics, including a history of being underweight and hypotonic in infancy, followed by a rapid onset of obesity, and distinct facial features. This presentation suggests a genetic or syndromic cause.

## **Why the Correct Answer is Right**
The description provided matches **Prader-Willi Syndrome (PWS)**, a genetic disorder caused by the loss of function of genes on chromosome 15 inherited from the father. Key features of PWS include:
- **Infantile hypotonia and failure to thrive**, which later transition into
- **Hyperphagia** (excessive hunger) leading to **obesity** if food intake is not strictly controlled.
- **Distinctive facial features** such as a narrow face, almond-shaped eyes, and a small mouth.
- **Behavioral problems**, including stubbornness, temper tantrums, and obsessive-compulsive behaviors.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Without the specific details of the option, we cannot directly address its incorrectness, but given the match of the description with PWS, any other option not aligning with these characteristics would be incorrect.
- **Option B:** Similarly, without specifics, we assume it does not fit the clinical picture of PWS as closely as the correct answer.
- **Option C:** This option is not provided, but presumably, it does not align with the clinical presentation described.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl in this case is the importance of **early diagnosis and strict dietary management** in PWS to prevent complications of obesity, such as type 2 diabetes, sleep apnea, and cardiovascular disease. Additionally, individuals with PWS often have **developmental delays** and **short stature**.

## **Correct Answer:** D. Prader-Willi Syndrome.