ICOS and common variable immunodeficiency: Mutations in several B-cell-related genes have been observed in a minority of patients with CVID, including 10% to 15% of patients with amino acid substitutions in Transmembrane activator and CAML interactor (TACI), less than 1% with deletion in Inducible T-cell co-stimulator (ICOS), and rare mutations in CD19 and B-cell activating factor receptor (BAFFR)[7, 8].