PIK3CD and Immunodeficiency: As it identifies the particular gain-of-function mutations in PIK3CD or PIK3R1 that define APDS, molecular diagnosis via genetic testing is the most dependable way of differentiation [10,12]. Functional experiments, including PI3Kδ overactivation research, can also show abnormal activation of the PI3K-AKT-mTOR pathway [13,46], further justifying the diagnosis. Understanding these differences is key to guaranteeing that patients receive the proper treatment since the therapy for APDS varies quite from that for other immunodeficiencies.