Study Objective: T cell receptor excision circles (TRECs) are episomal DNA circles excised from the T cell receptor genes during T cell maturation in the thymus. They do not replicate, so they are diluted out as T cells proliferate. Our objectives are to examine the levels of TRECs in blood samples from patients with primary immunodeficiency (PI) diseases; to determine which PI diseases might be detected by testing newborn dried blood spots for low numbers of TRECs; and to use the blood spots collected for future confirmatory or alternative tests to develop newborn screening for PIs.

Population: Patients diagnosed with defined primary T cell immunodeficiency diseases or undefined conditions with very low T cell numbers. There are several known, and additional unknown, gene defects that impair T lymphocyte maturation and function. The frequency of these rare disorders is unknown, but could potentially be learned in the course of population-based newborn screening.

Design: We will contact our network of immunology colleagues to help us identify and enroll patients already diagnosed with PI disorders. These patients will have had HIV ruled out as part of their immune evaluation. We will provide mail-in kits and will receive blood samples for analysis. We will attempt to retrieve the actual Guthrie cards containing the dried blood spots of these patients from their state screening laboratories to determine the number of TRECs that were present at birth in infants with these conditions.

Outcome Measures: We will measure TRECs in dried blood spots, and correlate TREC number with diagnosis and clinical and laboratory data. We hope to determine the range of immunodeficiency diseases that can be demonstrated to have significantly reduced TRECs as compared to healthy subjects using our assay. Because TREC testing may be insufficiently sensitive or specific as a stand-alone test, further tests may be developed and performed on the samples in the future, including DNA re-sequencing, detection of mRNA for T cell specific genes and/or proteins expressed only in T cells.