**Core Concept**
Rett syndrome is a neurodevelopmental disorder caused by mutations in the MECP2 gene, leading to severe intellectual disability, impaired speech, and distinctive hand movements. It is characterized by a triad of features: intellectual disability, loss of purposeful hand use, and distinctive hand stereotypies.

**Why the Correct Answer is Right**
Rett syndrome is a genetic disorder that affects the brain, leading to severe developmental delays and intellectual disability. The MECP2 gene plays a crucial role in brain development, and mutations in this gene disrupt normal brain function, resulting in the characteristic features of Rett syndrome. The disorder is typically diagnosed in early childhood, and affected individuals often require lifelong care and support.

**Why Each Wrong Option is Incorrect**
**Option A:** Microcephaly is not a characteristic feature of Rett syndrome, although some individuals may have a smaller head size. However, it is not a defining feature of the disorder.
**Option B:** Seizures are a common feature of Rett syndrome, occurring in approximately 70% of affected individuals. Therefore, this option is incorrect because seizures are indeed a characteristic of the disorder.
**Option C:** Autistic features are not typically seen in Rett syndrome, which is often characterized by a more profound intellectual disability and distinctive hand movements. While some individuals with Rett syndrome may exhibit behavioral problems, autistic features are not a defining feature of the disorder.

**Clinical Pearl / High-Yield Fact**
Rett syndrome is a genetic disorder that is typically diagnosed in early childhood, and affected individuals often require lifelong care and support. The disorder is caused by mutations in the MECP2 gene, which plays a crucial role in brain development.

**Correct Answer:** A. Microcephaly is not a characteristic feature of Rett syndrome, although some individuals may have a smaller head size.