Last, in contrast to STIM1 or ORAI1 or a few other T cell deficiencies with a normal number of circulating lymphocytes (8), our patients were generally lymphopenic (data S1 and Table 1), and abnormally low T cell receptor excision circles (TREC) levels were detected in the only patient (patient 4) screened at birth for severe T cell lymphopenia. Here, TBXT is linked to congenital T-cell immunodeficiency.