**Core Concept**
22q11 deletion syndrome, also known as DiGeorge syndrome, is a genetic disorder caused by a deletion on the long arm of chromosome 22. This deletion leads to various congenital anomalies, including thymic hypoplasia, parathyroid gland aplasia, and cardiac defects.

**Why the Correct Answer is Right**
The deletion affects the development of the third and fourth pharyngeal pouches, resulting in thymic hypoplasia and parathyroid gland aplasia. This leads to reduced T-cell production and hypocalcemia due to decreased parathyroid hormone production. The thymic hypoplasia impairs the development of T-cells, which are essential for cell-mediated immunity.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the deletion does not primarily affect the adrenal glands, which are located in the adrenal cortex and medulla. While there may be associated cardiovascular anomalies, the primary issues in DiGeorge syndrome are related to thymic hypoplasia and parathyroid gland aplasia.
* **Option B:** This option is incorrect because the deletion does not primarily affect the pancreas. While there may be associated gastrointestinal anomalies, the primary issues in DiGeorge syndrome are related to thymic hypoplasia and parathyroid gland aplasia.
* **Option C:** This option is incorrect because the deletion does not primarily affect the kidneys. While there may be associated cardiovascular anomalies, the primary issues in DiGeorge syndrome are related to thymic hypoplasia and parathyroid gland aplasia.

**Clinical Pearl / High-Yield Fact**
DiGeorge syndrome is associated with an increased risk of infections, particularly those caused by encapsulated organisms such as Streptococcus pneumoniae and Haemophilus influenzae. This is due to the impaired T-cell function and reduced antibody response.

**Correct Answer:** D. Cardiac defects