Tandem mass spectrometry, but not T-cell receptor excision circle analysis, identifies newborns with late-onset adenosine deaminase deficiency

BackgroundAdenosine deaminase (ADA)–severe combined immunodeficiency (SCID) is caused by genetic variants that disrupt the function of ADA. In its early-onset form, it is rapidly fatal to infants. Delayed or late-onset ADA-SCID is characterized by insidious progressive immunodeficiency that leads to permanent organ damage or death. Quantification of T-cell receptor excision circles (TRECs) or tandem mass spectrometry (tandem-MS) analysis of dried blood spots (DBSs) collected at birth can identify newborns with early-onset ADA-SCID and are used in screening programs. However, it is not clear whether these analyses can identify newborns who will have delayed or late-onset ADA-SCID before symptoms appear.ObjectiveWe performed a retrospective study to evaluate whether tandem-MS and quantitative TREC analyses of DBSs could identify newborns who had delayed-onset ADA-SCID later in life.MethodsWe tested stored DBSs collected at birth from 3 patients with delayed-onset ADA-SCID using tandem-MS (PCT EP2010/070517) to evaluate levels of adenosine and 2′-deoxyadenosine and real-time PCR to quantify TREC levels. We also analyzed DBSs from 3 newborns with early-onset ADA-SCID and 2 healthy newborn carriers of ADA deficiency.ResultsThe DBSs taken at birth from the 3 patients with delayed-onset ADA-SCID had adenosine levels of 10, 25, and 19 μmol/L (normal value, <1.5 μmol/L) and 2′-deoxyadenosine levels of 0.7, 2.7, and 2.4 μmol/L (normal value, <0.07 μmol/L); the mean levels of adenosine and 2′-deoxyadenosine were respectively 12.0- and 27.6-fold higher than normal values. DBSs taken at birth from all 3 patients with delayed-onset ADA deficiency had normal TREC levels, but TRECs were undetectable in blood samples taken from the same patients at the time of diagnosis.ConclusionTandem-MS but not TREC quantification identifies newborns with delayed- or late-onset ADA deficiency.