The results also revealed that genetic variants shared by both twins in CVID-related genes such as TNFRSF13B, NFKB2, CR2, and CD19, which strengthens the hypothesis that another change, such as environmental exposure and epigenetic modifications, may be critical factors in the discordant phenotype of these twins [83]. This evidence concerns the gene NFKB2 and common variable immunodeficiency.