Depending on the number of genetic modifier loci, the analysis of a large sample of TNFRSF13B mutation carriers will be needed to determine whether a specific combination of genetic markers (including the TNFRSF13B mutation) is associated with a specific phenotype or predisposition to the common features of PAD, including infections, autoimmunity, lymphoproliferation, or malignancy. The gene discussed is TNFRSF13B; the disease is infection.