Of note, we identified genetic variants shared by both CVID-discordant twins affecting genes previously associated with CVID, such as CR2, NFKB2, CD19 and TNFRSF13B. This observation reinforces the hypothesis that additional alterations, such as epigenetic changes, might be contributing factors to the differential phenotype of these siblings to the development of CVID. This evidence concerns the gene CD19 and common variable immunodeficiency.