Basic and clinical immunology
Development of population-based newborn screening for severe combined immunodeficiency

https://doi.org/10.1016/j.jaci.2004.10.012Get rights and content

Background

Severe combined immunodeficiency (SCID) is a treatable, inherited lack of cellular and humoral immunity caused by diverse mutations in several different genes and leading to death in infancy unless immune reconstitution is provided. Currently no population screening exists for SCID, but early diagnosis would improve outcome.

Objective

Because all patients with SCID make few or no T cells, we asked whether the absence of T-cell receptor excision circles (TRECs), DNA episomes in newly formed T cells, could identify SCID regardless of genotype.

Methods

DNA isolated from dried blood spots was assayed by real-time PCR to quantitate TRECs. Control PCR was performed on a segment of the β-actin gene. After pilot studies with adult and cord blood control subjects, blood from SCID patients was spotted onto filters and tested, followed by screening of actual blood spots from the Maryland Newborn Screening Program. Finally, newborn blood spots were recovered and tested from 2 infants after their diagnosis of SCID.

Results

In contrast to filters from the newborn screening program, which had a mean of 1020 TRECs in two 3-mm punches, samples from 23 infants with SCID had <30 TRECs. The newborn screening filter was retrieved from a state laboratory for one of these infants plus another infant who had died of SCID previously; although both samples had detectable β-actin DNA, neither had TRECs.

Conclusion

TRECs are a stable analyte that can identify T-cell lymphopenia in newborn dried blood spots so that infants with SCID can receive early, life-saving treatment.

Section snippets

Samples

Blood samples from healthy adults and from infants newly diagnosed with SCID were donated with consent under approved research protocols at the National Institutes of Health. SCID molecular diagnosis was performed by sequencing IL2RG in male subjects as described16 and obtaining JAK3 sequence (GeneDx, Rockville, Md) where indicated. Umbilical cord blood was obtained from routine deliveries via the National Disease Research Interchange (Philadelphia, Pa). Simulated blood spots were made by

Results

Although simple to collect, dried blood spots vary widely in cellular content and extractable material, as illustrated by the 10-fold variation in DNA yields in our samples from 0.12 to 1.35 μg (mean, 0.46 μg) per 2 punches. Nonetheless, preliminary experiments showed significant positive correlations between TRECs and DNA content; β-actin copies and DNA content; and TRECs and β-actin copies (not shown). Multiple independent DNA preparations and PCR reactions were performed on a series of spots

Discussion

This study addresses previously unsatisfied criteria for newborn population screening for SCID: unavailability of incidence data and absence of an appropriate screening test. Paradoxically, the true incidence of SCID will be learned only through population screening. However, a minimum incidence can be estimated from our identification of 19 infants with XSCID mutations in a year and the annual US birthrate of 4,000,000.32 If blood from every XSCID infant born in the US were submitted to our

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    Supported by National Human Genome Research Institute Division of Intramural Research, National Institutes of Health.

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