Thymic hypoplasia is seen in
**Core Concept**
Thymic hypoplasia refers to the underdevelopment of the thymus gland, a crucial organ responsible for the maturation and selection of T-lymphocytes (T cells) in the immune system. This condition can lead to impaired T-cell function and increased susceptibility to infections and autoimmune disorders.
**Why the Correct Answer is Right**
Thymic hypoplasia is often associated with DiGeorge syndrome, a genetic disorder characterized by thymic aplasia or hypoplasia, parathyroid gland abnormalities, and cardiac defects. The condition is caused by a deletion of the long arm of chromosome 22 (22q11.2 deletion syndrome). This deletion leads to impaired development of the third and fourth pharyngeal pouches, resulting in thymic hypoplasia and other associated anomalies.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately describe a condition associated with thymic hypoplasia.
**Option B:** This option is incorrect as it refers to a condition characterized by thymus hyperplasia, not hypoplasia.
**Option C:** This option is incorrect as it is a condition associated with thymic hyperplasia and is not related to thymic hypoplasia.
**Clinical Pearl / High-Yield Fact**
DiGeorge syndrome should be considered in patients with recurrent infections, congenital heart disease, and hypocalcemia, as it often presents with a triad of these symptoms.
**Correct Answer: D. DiGeorge syndrome**