**Core Concept**
The patient's symptoms suggest a condition known as Alport syndrome, characterized by a triad of congenital glomerulonephritis, hearing loss, and otopalatodigital syndrome (OPD) spectrum disorders. However, the key aspect here is the presence of a cleft palate and hypocalcemia, which points towards a condition known as DiGeorge syndrome or 22q11.2 deletion syndrome. This syndrome is caused by a deletion in the long arm of chromosome 22 and is associated with thymic hypoplasia, which can lead to immunodeficiency.

**Why the Correct Answer is Right**
The correct answer involves understanding the relationship between the thymus and the lymphoid organs. The thymus plays a crucial role in the development and maturation of T-lymphocytes. In DiGeorge syndrome, the thymic hypoplasia results in reduced T-cell production, which affects the lymphoid organs. The periaeriolar lymphoid sheath (PALS) of the spleen is a critical component of the immune response, responsible for the activation and proliferation of T-cells. With reduced T-cell production, the PALS of the spleen would be expected to be decreased in size.

**Why Each Wrong Option is Incorrect**
* **Option B:** Increased size of splenic follicles is not expected in DiGeorge syndrome. Splenic follicles are primarily involved in the humoral immune response, which is not directly affected in this condition.
* **Option C:** Increased size of para cortical areas of lymph nodes is not a characteristic feature of DiGeorge syndrome. The para cortical areas are involved in the immune response, but the key issue in this condition is the reduction in T-cell production, which would not lead to an increase in these areas.
* **Option D:** Decreased size of germinal centres of lymph nodes is not a direct consequence of DiGeorge syndrome. The germinal centres are involved in the humoral immune response, and while they may be affected indirectly due to reduced T-cell help, the primary issue is the reduction in T-cell production.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that DiGeorge syndrome is associated with a characteristic facial appearance, which includes a small chin, narrow palate, and low-set ears. Additionally, the presence of cleft palate and hypocalcemia should raise suspicion for this condition.

**✓ Correct Answer: A. Decreased size of periaeriolar lymphoid sheath of spleen**