A high-throughput TREC- and KREC-based newborn screening for severe inborn errors of immunity.

INTRODUCTION: Severe combined immunodeficiency (SCID) due to T-cell deficiency is the most severe form of inborn error of immunity (IEI). It frequently leads to severe and recurrent infections and the first infection or live vaccines can sometimes be fatal. Patients with B-cell deficiency (BCD), such as X-linked agammaglobulinaemia (XLA), also suffer from severe or recurrent infections. Thus, early diagnosis via newborn screening (NBS) is suitable for these types of diseases. We developed a lyophylized TaqMan-based quantitative polymerase chain reaction (qPCR) kit with primers and probes for the simultaneous detection of T-cell receptor excision circles (TREC) and κ-deleting recombination excision circles (KREC). We also developed a fully automated DNA extraction and purification process using Magtration technology from dried blood spots (DBS), enabling high-throughput analysis METHODS: We examined 15,258 stored DBS collected from 2014 to 2015 by this method. Newborn screening samples from children with a known SCID, XLA or ataxia-telangiectasia (AT) were also examined as positive controls.

RESULTS: RPPH1 (internal control), TREC, and KREC all had near-normal distributions. One specimen was below the cut-off for TREC (0.00657%) after exclusion of 36 specimens due to the failure of DNA extraction (0.23%). The TREC levels in the patients with AT and SCID, and KREC levels in the patients with AT and XLA were all below cut-off or absent.

CONCLUSIONS: This assay would allow the establishment of qPCR-based NBS in unfamiliar laboratories leading to the early diagnosis of SCID and BCD.