Neonatal screening for severe combinedimmunodeficiency caused by an adenosine deaminase defect: a reliable andinexpensive method using tandem mass spectrometry.

Background: Adenosine deaminase (ADA)–severe combined immunodeficiency (SCID) is an SCID caused by a defect in the enzyme adenosine deaminase. It is usually fatal in infancy because of severe recurrent infections. When diagnosis is made, permanent damage caused by infections or by metabolites is often present. Gene therapy, bone marrow transplantation, or enzyme therapy might be effective if performed early. ADA-SCID complies with all the criteria for inclusion in a newborn screening program. However, screening methods are still expensive or provide a non-negligible number of indeterminate results. Objective: The aim of the present study was to develop a simple, reliable, and inexpensive method for diagnosis of ADA-SCID by using dried blood spot (DBS) samples taken at birth. Cost per test was calculated, including the cost for reagents, equipment, and operators. Methods: DBS samples from 4 patients with genetically confirmed ADA-SCID and 12,020 DBS samples from healthy newborns were examined. Adenosine and 29-deoxyadenosine were tested by using tandem mass spectrometry (PCT EP2010/ 070517). Results: The mean levels of adenosine and 29-deoxyadenosine were 7.8 6 3.1 and 8.5 6 6.0 mmol/L, respectively, in affected children; adenosine was found at 0.23 6 0.09 mmol/L, whereas 29-deoxyadenosine was never detected in healthy control subjects (adenosine: P < 1026 [95% confidence limit, 7.59-7.78] and 29-deoxyadenosine: P < 1026 [95% confidence limit, 8.65-8.82] for control subjects vs patients with ADA-SCID). No indeterminate or false-positive results were found. Cost per test was V0.01 ($0.013). A pilot population-based newborn screening for ADA-SCID has started in Tuscany, Italy. Conclusion: Tandem mass spectrometry can be used for diagnosis of one of the most frequent form of SCID at a negligible cost.