TNFSF12 and common variable immunodeficiency: Monogenic CVID, particularly NFKB1, NFKB2, IKZF1, TNFSF12 and ICOS mutations, are all reported in viral illnesses, and should be investigated for in severe cases, particularly if there are other associated factors, such as the lymphoproliferative disease seen in NFKB1 LOF.