Current diagnostic features for CVID, according to the European Society for Immunodeficiencies (ESID)/Pan American Group for Immune Deficiency (PAGID) (1999), ESID (2014) and new diagnostic criteria proposed by Ameratunga et al. [13] for CVID, include reduction in levels of serum IgG in combination with low levels of IgA with or without low levels of IgM, poor or absent response to immunizations and/or low number of switched memory B cells and an absence of any other defined immunodeficiency states [14]. The gene discussed is CD40LG; the disease is common variable immunodeficiency.