What deficiency is typically seen in patients with DiGeorge syndrome?

DiGeorge syndrome is primarily characterized by a deficiency in T cells, which results from a developmental defect in the third and fourth pharyngeal pouches during embryogenesis. These pouches are responsible for forming the thymus and parathyroid glands, both of which are crucial for the immune system. The thymus is essential for the maturation of T lymphocytes (T cells), so when it's underdeveloped or absent, patients exhibit a significant reduction in T cell levels. This leads to immunodeficiency, making individuals more susceptible to infections.

While the other deficiencies listed may occur due to various pathological processes, they are not the defining characteristics of DiGeorge syndrome. Iron deficiency anemia is related to nutritional factors rather than the genetic and developmental issues seen in DiGeorge. Vitamin D deficiency and calcium deficiency can also be associated with various health conditions but are not specific to the syndrome. The hallmark of DiGeorge syndrome is indeed the T cell deficiency, which profoundly impacts the patient's overall immune function.