Angelman syndrome is due to
## **Core Concept**
Angelman syndrome is a genetic disorder primarily characterized by developmental delays, intellectual disability, severe speech impairment, and microcephaly. It is often associated with a deletion on chromosome 15 inherited from the mother. The underlying principle involves the loss of function of the **UBE3A** gene, which is crucial for normal neurological development.
## **Why the Correct Answer is Right**
The correct answer involves the deletion of the maternal copy of chromosome 15, specifically the region that includes the **UBE3A** gene. This gene is paternally imprinted, meaning it is normally expressed only from the maternal allele in the brain. A deletion or mutation affecting the maternal allele leads to the absence of UBE3A protein in the brain, causing Angelman syndrome. This is a classic example of a disorder caused by the loss of a maternal gene due to genomic imprinting.
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because Angelman syndrome is not caused by a duplication of the paternal chromosome 15. However, a similar condition, Prader-Willi syndrome, results from the loss of function of genes on the paternal copy of chromosome 15.
- **Option B:** This option is incorrect because the syndrome is specifically related to the maternal copy of chromosome 15, not the paternal copy. The paternal copy of the UBE3A gene is usually imprinted and silenced.
- **Option C:** While this option might seem plausible because it mentions a deletion, it does not specify the parental origin of the deleted chromosome 15. Angelman syndrome is associated with a deletion on the maternal chromosome 15.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that patients with Angelman syndrome often exhibit a happy demeanor with frequent laughter, which is a distinctive feature of the disorder. Additionally, the condition is associated with a characteristic EEG pattern and a high risk of seizures.
## **Correct Answer:** . Deletion of maternal chromosome 15.