## Core Concept
Rett's syndrome is a genetic disorder that primarily affects girls, causing severe mental and physical disability. It is characterized by normal early growth and development followed by a slowing of development, intellectual disability, and physical disability. The disorder is caused by mutations in the MECP2 gene.

## Why the Correct Answer is Right
The MECP2 gene provides instructions for making a protein called methyl-CpG-binding protein 2, which is essential for normal brain function. Mutations in this gene lead to Rett's syndrome by disrupting the normal functioning of neurons. The syndrome is not caused by a deficiency in dopamine or problems with the dopamine pathway directly; rather, it's related to the MECP2 gene mutation affecting brain development.

## Why Each Wrong Option is Incorrect
* **Option A:** Not provided, but typically, options related to Rett's syndrome might include statements about MECP2 gene mutation being the cause, which would be true.
* **Option B:** Similarly, not provided, but if it stated something about the syndrome's effects on physical and mental development, it could be true.
* **Option C:** Without specifics, if an option suggested a link to a metabolic disorder or another genetic cause, it would be incorrect because Rett's syndrome is primarily associated with MECP2 mutations.
* **Option D:** Given as the correct answer but without context, we assume it provides a statement that does not align with known facts about Rett's syndrome.

## Clinical Pearl / High-Yield Fact
A key clinical pearl for Rett's syndrome is that it predominantly affects girls. This is because the MECP2 gene is located on the X chromosome, and girls have two X chromosomes. A mutation in one of the X chromosomes can lead to the syndrome, while boys, having only one X chromosome, usually do not survive if they inherit the mutated gene.

## Correct Answer: D.