**Core Concept**
Rett's syndrome is a rare genetic disorder primarily affecting females, characterized by mental and physical disability. It is caused by mutations in a specific gene that plays a crucial role in brain development.

**Why the Correct Answer is Right**
The correct answer is the gene responsible for encoding a protein essential for neuronal growth and brain development. The protein, called MeCP2 (methyl CpG-binding protein 2), is involved in the regulation of gene expression and is crucial for normal brain function. Mutations in the MECP2 gene lead to impaired neuronal growth and development, resulting in the characteristic features of Rett's syndrome, including intellectual disability, seizures, and motor dysfunction.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not correspond to any known gene associated with Rett's syndrome.
* **Option B:** This option is incorrect because it refers to a gene involved in a different genetic disorder, such as muscular dystrophy.
* **Option C:** This option is incorrect because it is a gene involved in a different type of genetic disorder, such as sickle cell anemia.

**Clinical Pearl / High-Yield Fact**
Rett's syndrome is an X-linked dominant disorder, meaning that the mutated gene is located on the X chromosome and only affects females, who inherit one X chromosome from each parent. Males with the mutation typically do not survive infancy due to the absence of one X chromosome.

**Correct Answer: C. MECP2**