Final answer:
DiGeorge syndrome is connected to T cell deficiency and pertains to the development of the thymus gland, while Severe Combined Immunodeficiency (SCID) affects both B-cell and T-cell functions, leading to nearly no adaptive immunity.
Step-by-step explanation:
DiGeorge syndrome, also known as thymic aplasia, is primarily associated with T cell deficiency due to aberrations in the development of the thymus gland. This congenital condition, which can lead to a reduction or absence of T cell production, is often a result of a deletion on chromosome 22. Consequently, affected individuals can exhibit various immune system deficiencies and are susceptible to a range of infections.
One disorder that is characterized by a lack of both B and T cells is Severe Combined Immunodeficiency (SCID). This genetic disease leads to a nearly complete absence of adaptive immunity, leaving individuals with SCID extremely vulnerable to infections. Unlike DiGeorge syndrome, which primarily affects T cells, SCID affects both T-cell dependent antibody responses and cell-mediated immune responses due to defects in both B-cell and T-cell functions. The severity of SCID is such that it is often diagnosed within the first few months of life following the occurrence of severe, opportunistic infections.