Clinical complications such as recurrent respiratory infections, adenopathy and intestinal problems are together with frequently reported immunological abnormalities (increased IgM serum level associated to increased frequency of transitional/immature B cells and of effector/memory CD8 T cells as well as persistent CMV and/or EBV viremia) first and major diagnostic indications to consider further investigation of the PI3Kδ signaling activation. The gene discussed is CD40LG; the disease is lymphatic system disorder.