Which of the following syndromes involves a deficiency in both humoral and cellular immunity due to a genetic defect in T and B cell functions?

Severe Combined Immunodeficiency (SCID) is characterized by a genetic defect that affects the development and function of both T cells and B cells, leading to a severe deficiency in both humoral and cellular immunity. Individuals with SCID typically present with recurrent infections due to their inability to mount effective immune responses against pathogens. This disorder can be caused by various genetic mutations, such as those affecting the IL2RG gene or adenosine deaminase (ADA), which are crucial for T and B cell maturation.

In this context, SCID represents a complete failure of both branches of the adaptive immune system, differentiating it from other syndromes mentioned in the options. Wiskott-Aldrich syndrome involves issues primarily related to antibody production and thrombocytopenia, DiGeorge syndrome results from thymic hypoplasia impacting T cell development predominantly, and X-Linked Agammaglobulinemia is primarily a deficiency in humoral immunity due to a defect in B cell maturation. SCID, therefore, is the only condition listed that systematically affects both T and B cells, leading to profound immunodeficiency.