## **Core Concept**
DiGeorge syndrome, also known as 22q11.2 deletion syndrome, is a disorder characterized by a defect in the development of the pharyngeal pouch system. This leads to various clinical manifestations, including congenital heart problems, cleft palate, and immunodeficiency due to thymic hypoplasia. The condition is associated with a deletion on chromosome 22.

## **Why the Correct Answer is Right**
The correct answer, , is associated with DiGeorge syndrome because this condition results from a deletion on chromosome 22 (22q11.2 deletion). This deletion affects the development of the third and fourth pharyngeal pouches, which are crucial for the formation of the thymus and parathyroid glands. The thymic hypoplasia or aplasia leads to reduced T-cell production, causing immunodeficiency.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not specify a chromosomal abnormality or a specific gene deletion associated with DiGeorge syndrome.
- **Option B:** This option is incorrect as it does not relate to the known genetic cause of DiGeorge syndrome.
- **Option D:** This option is incorrect because it does not accurately represent the genetic defect seen in DiGeorge syndrome.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl for DiGeorge syndrome is that patients often present with the "4 Cs": Congenital heart problems, Cleft palate, Characteristic facial features, and Cellular immunodeficiency due to thymic hypoplasia. Remembering these features can help in identifying the syndrome.

## **Correct Answer Line**
**Correct Answer: C. 22q11.2 deletion.**