Activated phosphoinositide 3-kinase delta syndrome (APDS) is caused by heterozygous gain of function mutations in pi3kδ catalytic p110δ (pik3cd) or regulatory p85α (pik3r1) subunits leading to APDS1 and APDS2, respectively (64). The gene discussed is PIK3CD; the disease is activated PI3K-delta syndrome.