In addition, a reduction in recent thymic emigrants (CD45RA+CD31+) was also shown.6, 58 Finally, the T-cell receptor excision circle (TREC) is a gene segment by-product of VDJ rearrangement not replicated during cell division and is considered as the gold standard in measuring thymic output and recent thymic emigrants.59 As much as a 10× fold reduction in TREC was reported in both CD4 and CD8 T cells of patients with CVID when compared with age-matched healthy controls.60, 61. This evidence concerns the gene CD4 and common variable immunodeficiency.