Such combined SCID/RTE + PIDOT tube approach will also be useful for positive cases from newborn screening (NBS) programs, i.e., cases with strongly reduced T-cell receptor excision circles (TRECs) in blood (14, 75–77).Whenever specific diseases such as ALPS or XLP are suspected (e.g., increased CD4−/CD8− counts or increased total T-cells counts; Figure 1B) additional studies need to be performed (not addressed in this manuscript). This evidence concerns the gene CD4 and X-linked lymphoproliferative disease.