Patients of all ages who have given informed consentfor participation in the ESID online Registry and fulfill the ESID ClinicalWorking Definitions for ‘unclassified antibody deficiency’, ‘deficiency ofspecific IgG’, ‘IgA with IgG subclass deficiency’, ‘isolated IgG subclassdeficiency’, ‘selective IgM deficiency’, ‘selective IgA deficiency’ or‘common variable immunodeficiency’ will be included. The gene discussed is CD79A; the disease is Decreased circulating total IgM.