Outcomes of the first 6.5 years of Newborn Screening for Severe Combined ImmunoDeficiencies in New Zealand

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Introduction: Severe combined immunodeficiencies (SCID) are rare and fatal heterogenous congenital disorders characterised by profound impairment of T lymphocyte development. Newborn screening for SCID by quantification of T-cell receptor excision circles (TRECs) was introduced to the New Zealand Newborn Screening Programme in December 2017 (1). We report screening outcomes over the first 6.5 years of screening. Method: TRECs were measured using the EnliteTM Neonatal TREC kit on dried blood spots as part of national newborn screening. Out-of-range results, including those remaining below TREC cut-off after second screening sample, were referred for flow cytometry diagnostic testing, with clinically important T-cell lymphopenia (TCL) defined as ≤1500×106/L; or CD4 naïve T cell count (CD45RA/CD62L) ≤200×106/L or ≤50%, as previously described (1). SCID and complete athymia were primary screening targets. Results: 371948 infants were screened between 7th December 2017 and 6th June 2023. 111 (0.03%) babies had out-of-range results requiring referral, of whom eight were deceased prior to flow cytometry (inconclusive), and 65 (59%) had normal T-cell subsets on diagnostic testing. 58 (52%) were screened in NICU. Five (0.001%) met the primary target (one ARTEMIS–deficient SCID, one MTHFD1-deficient atypical SCID, one atypical SCID unknown, one complete DiGeorge syndrome, and one athymia secondary to CHARGE syndrome). Three had definitive treatment, and two are deceased from a non-SCID cause in the neonatal period. Thirty-three had non-SCID TCL (33%), of whom eleven had syndromic TCL (excluding complete athymia), 5 idiopathic, 12 secondary, and five due to preterm birth alone. There have been no missed cases since screening implementation. Conclusion: SCID newborn screening has been successfully integrated into New Zealand Newborn Screening and identified 5 patients with SCID or complete athymia over the first 6.5 years. Our screen-detected SCID data match the expected population frequency of SCID of 1:50-100000. References: (1) Heather, N., de Hora, M., Brothers, S., Grainger, P., Knoll, D., Webster, D. Introducing Newborn Screening for Severe Combined Immunodeficiency—The New Zealand Experience. Int J Neonatal Screen. 2022;8(2):33. (2) Blom, M., Zetterström, R., Stray-Pedersen, A., Gilmour, K., Gennery, A., Puck, J., van der Burg, M. Recommendations for Uniform Definitions used in Newborn Screening for Severe Combined Immunodeficiency. JACI 2022;149(4):1428–1436.

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