ICOS and common variable immunodeficiency: In these patients, in whom a monogenic background of CVID was identified, variants in genes, such as cytotoxic T lymphocyte antigen 4 (CTLA4), lipopolysaccharide (LPS)-responsive beige-like anchor protein (LRBA), BTB domain and CNC homolog 2 (BACH2) [17,18], nuclear factor kappa B subunit 1 (NF-kB1) [17,18,19], signal transducer and activator of transcription 3 (STAT3) [18,20], phosphoinositide 3-kinase (PI3K), inducible T-cell costimulator (ICOS), IKAROS family zinc finger 1 (IKZF1), or interferon regulatory factor 2-binding protein 2 (IRF2BP2) [19] were demonstrated.