The TREC/KREC Assay for the Diagnosis and Monitoring of Patients with DiGeorge Syndrome

<div><p></p><p>DiGeorge syndrome (DGS) presents with a wide spectrum of thymic pathologies. Nationwide neonatal screening programs of lymphocyte production using T-cell recombination excision circles (TREC) have repeatedly identified patients with DGS. We tested what proportion of DGS patients could be identified at birth by combined TREC and kappa-deleting element recombination circle (KREC) screening. Furthermore, we followed TREC/KREC levels in peripheral blood (PB) to monitor postnatal changes in lymphocyte production.</p><p>Methods</p><p>TREC/KREC copies were assessed by quantitative PCR (qPCR) and were related to the albumin control gene in dry blood spots (DBSs) from control (n = 56), severe immunodeficiency syndrome (SCID, n = 10) and DGS (n = 13) newborns. PB was evaluated in DGS children (n = 32), in diagnostic samples from SCID babies (n = 5) and in 91 controls.</p><p>Results</p><p>All but one DGS patient had TREC levels in the normal range at birth, albeit quantitative TREC values were significantly lower in the DGS cohort. One patient had slightly reduced KREC at birth. Postnatal DGS samples revealed reduced TREC numbers in 5 of 32 (16%) patients, whereas KREC copy numbers were similar to controls. Both TREC and KREC levels showed a more pronounced decrease with age in DGS patients than in controls (p<0.0001 for both in a linear model). DGS patients had higher percentages of NK cells at the expense of T cells (p<0.0001). The patients with reduced TREC levels had repeated infections in infancy and developed allergy and/or autoimmunity, but they were not strikingly different from other patients. In 12 DGS patients with paired DBS and blood samples, the TREC/KREC levels were mostly stable or increased and showed similar kinetics in respective patients.</p><p>Conclusions</p><p>The combined TREC/KREC approach with correction via control gene identified 1 of 13 (8%) of DiGeorge syndrome patients at birth in our cohort. The majority of patients had TREC/KREC levels in the normal range.</p></div

Quantitative levels of TRECs (A) KRECs (B), relative T cell (CD3^pos) counts (C), relative B cell (CD19^pos) counts (D), absolute T cell counts (E), absolute B cell counts (F), absolute lymphocyte counts (G) and relative NK cell (CD3^negCD16^posCD56^pos) counts (H) in relation to age (x-axis) in patients with DiGeorge syndrome (black diamonds) and in controls (empty diamonds).

<p>Lines show linear regression analyses for patients (full lines) and controls (dotted lines).</p

Quantitative TREC/KREC levels expressed as number of copies per microgram of DNA in A) neonatal dry blood spots B) peripheral blood for control children vs. children with DiGeorge syndrome (0–18 years).

<p>Quantitative TREC/KREC levels expressed as number of copies per microgram of DNA in A) neonatal dry blood spots B) peripheral blood for control children vs. children with DiGeorge syndrome (0–18 years).</p

TREC and KREC numbers expressed as copies per microgram of DNA in A) neonatal dry blood spots B) peripheral blood in children (0–18 years) for controls, patients with DiGeorge syndrome and patients with severe combined immunodeficiency (SCID).

<p>Grey areas represent the abnormal TREC/KREC range.</p