**Question:** Angelman syndrome is due to -

A. UBE3A gene mutation
B. Prader-Willi syndrome
C. Paternal deletion of chromosome 15
D. Brain abnormality

**Correct Answer:** C. Paternal deletion of chromosome 15

**Core Concept:** Angelman syndrome is a neurodevelopmental disorder characterized by global developmental delay, severe speech impairment, ataxia, and characteristic facial features. It is caused by various genetic abnormalities affecting the UBE3A gene, which is located on chromosome 15.

**Why the Correct Answer is Right:** Angelman syndrome is primarily caused by a paternal deletion of chromosome 15 (Option C). This deletion results in the absence of the UBE3A gene expression in the brain, leading to the characteristic symptoms seen in Angelman syndrome patients. The UBE3A gene plays a crucial role in neuronal development and function, particularly in the hippocampus and cortex, areas that are essential for learning, memory, and motor control.

**Why Each Wrong Option is Incorrect:**

A. UBE3A gene mutation (Option A) is a cause of Angelman syndrome, but it is not the primary mechanism. While a mutation in the UBE3A gene can lead to loss of function, it is the absence of the UBE3A gene expression due to the paternal deletion of chromosome 15 that directly impacts neuronal development and function, leading to the syndrome.

B. Prader-Willi syndrome (Option B) is a different genetic disorder caused by a maternal deletion of chromosome 15, involving the same gene (UBE3A) but with opposite effects (increased gene expression) and distinct clinical manifestations.

D. Brain abnormality (Option D) is a broad term that could be related to other neurological disorders, but does not specifically address the genetic cause of Angelman syndrome. The core clinical feature of Angelman syndrome is the absence of UBE3A gene expression, primarily due to paternal deletion of chromosome 15.

**Clinical Pearl:** The relationship between genetic abnormalities, neuronal development, and the resulting clinical features in Angelman syndrome highlights the importance of understanding genetic causes and their impact on neuronal function in understanding complex neurodevelopmental disorders.