**Question:** All of the following are characteristics of Rett syndrome EXCEPT

A. Seizures
B. Obesity
C. Hypotonia
D. Dysmorphic features

**Core Concept:**
Rett syndrome is a neurodevelopmental disorder primarily affecting girls caused by mutations in the MECP2 gene. It is characterized by regression of previously acquired motor skills, cognitive decline, loss of purposeful hand use, seizures, and respiratory problems. However, obesity is not a typical feature of Rett syndrome. While weight gain and increased appetite may occur in some patients, the overall body composition remains normal or even lean. Obesity is more commonly associated with other conditions, such as Prader-Willi syndrome, which has different genetic causes and clinical features.

**Why the Correct Answer is Right:**
In Rett syndrome, the primary features focus on motor skills regression, cognitive decline, and respiratory complications. Obesity, although a potential consequence in some cases, is not a defining characteristic of the syndrome. It is essential to differentiate Rett syndrome from other disorders that may present with obesity, like Prader-Willi syndrome, as they have distinct genetic causes and clinical manifestations.

**Why Each Wrong Option is Incorrect:**

A. Seizures are a common feature of Rett syndrome, occurring in approximately 80% of cases. They are typically complex partial seizures, often misinterpreted as growth seizures or developmental regression.

B. Obesity is not a typical feature of Rett syndrome, as mentioned above. Instead, weight gain and increased appetite may occur, but overall body composition remains lean.

C. Hypotonia or decreased muscle tone is a hallmark of Rett syndrome, affecting motor development and increasing the risk of respiratory complications.

D. Dysmorphic features are not a key component of Rett syndrome diagnosis. Dysmorphic features are more commonly seen in other genetic syndromes or disorders, such as Prader-Willi syndrome, which has distinct clinical manifestations and genetic basis.

**Clinical Pearl:**
When assessing patients with suspected Rett syndrome, it is vital to differentiate between Rett syndrome and disorders with overlapping features, like Prader-Willi syndrome. While some symptoms like seizures, hypotonia, and respiratory complications are shared between these two conditions, the genetic basis and dysmorphic features are distinctive. Rett syndrome is caused by mutations in the MECP2 gene, while Prader-Willi syndrome is associated with a deletion on chromosome 15. Recognizing these differences can guide appropriate genetic testing and treatment strategies.