Primary immunodeficiency disorders (PID) comprise a group of more than 200 different diseases. Major efforts are currently being undertaken to develop methods for detection of the clinically most severe forms in the neonatal period. Polymerase chain reaction (PCR)-based detection of signal joint T cell receptor excision circles (TRECs), extracted from Guthrie cards, has already proved to be a valuable tool for identifying children with T cell lymphopenia, including patients with severe combined immunodeficiencies (SCID) 1, and is now carried out routinely in selected states in the United States. Recently, a similar method for analysis of B cell κ-deleting excision circles (KRECs) was developed 2, allowing identification of patients with B cell lymphopenia for the detection of patients with X-linked agammaglobulinaemia (XLA).
To evaluate the possibilities for neonatal screening for different forms of PID, we combined the TREC and KREC assays into a triplex PCR method and evaluated its potential in a large number of anonymized control samples and retrospective samples from patients with a variety of PIDs 3.
Retrospective samples from patients with SCID and XLA were identified easily, and the former could also be assigned to subgroups (T−B+, T−B−). In addition, patients with ataxia–telangiectasia, dedicator of cytokinesis 8 (DOCK8) mutations and Nijmegen breakage syndrome showed low frequencies of TRECs and/or KRECs. However, patients with selective immunoglobulin (Ig)A deficiency, hyper-IgM or common variable immunodeficiency could not be identified 3,4.
‘Additional positive’ results were observed in a proportion of prematurely born children and in those with trisomy 21 (Down syndrome) 4 and DiGeorge syndrome 5. The reduced number of TRECs in approximately one-third of the latter patients appeared to correlate with disease severity. Second-tier tests were also developed to identify the two latter disorders. Selected patients with Wiskott–Aldrich syndrome also showed reduced TREC/KREC numbers 6. Initial screening of 20 000 anonymized Guthrie cards from Swedish and German children helped to define suitable cut-off values that would allow identification of patients with suspected PID, and an open prospective pilot trial in Sweden was initiated in November 2013. This trial will run for 3 years, followed by an evaluation of the results. It currently covers approximately one-third of all newborn children in Sweden (the Stockholm region) and will subsequently, if successful, be implemented nationwide.
In conclusion, neonatal screening for severe forms of PID is feasible and fulfils the Wilson–Jungner criteria 7,8. This screening will help to identify newborn children with a variety of PID, allowing early diagnosis and therapy.
Acknowledgments
The presented work has been performed mainly by Stephan Borte and the samples have been obtained from the Swedish Screening Centre for Metabolic Diseases (CMMS; Ulrika von Döbeln).
Disclosure
Part of the costs for the ongoing trial is being covered by an unrestricted research grant from Baxter Healthcare.
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