## **Core Concept**
DiGeorge's 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's syndrome because the 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. The parathyroid gland abnormalities result in hypocalcemia.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately represent the genetic abnormality associated with DiGeorge's syndrome.
- **Option B:** This option is incorrect as it does not correspond to the specific chromosomal deletion seen in DiGeorge's syndrome.
- **Option D:** This option is incorrect because it does not accurately describe the genetic defect found in DiGeorge's syndrome.

## **Clinical Pearl / High-Yield Fact**
A key clinical feature of DiGeorge's syndrome is the triad of congenital heart disease, cleft palate, and hypocalcemia. The immunodeficiency aspect makes patients susceptible to infections. A classic mnemonic to remember some features of DiGeorge syndrome is "CATCH 22": Cardiac defects, Abnormal facies, Thymic hypoplasia, Cleft palate, and Hypocalcemia, with the "22" referring to the chromosome 22 deletion.

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