CD79A and hyperinsulinemic hypoglycemia, familial, 4: CVID is a diagnosis of exclusion and, therefore, requires specific testing to hone in on a definitive diagnosis [6]. One definitive characteristic of CVID is the presence of hypogammaglobulinemia with reduced IgA and, sometimes, concomitant IgM deficiency [1]. CVID patients, in addition to reduced IgA and IgM levels, may also have poor vaccine response and frequent sinopulmonary infections (which is also common among those who are only IgG deficient) [1].