Capillary Electrophoresis in Diagnosis and Monitoring of Adenosine Deaminase Deficiency

Background: The diagnosis and monitoring of severe combined immunodeficiency disease (SCID) attributable to adenosine deaminase (ADA) deficiency requires measurements of ADA, purine nucleoside phosphorylase (PNP), and S-adenosyl-L-homocysteine-hydrolase (SAHH) activity and of deoxyadenosine metabolites. We developed capillary electrophoresis (CE) methods for the detection of key diagnostic metabolites and evaluation of enzyme activities. Methods: Deoxyadenosine metabolites were separated in 30 mmol/L sodium borate-10 mmol/L sodium dodecyl sulfate (pH 9.80) at 25°C on a 60-cm uncoated capillary. For determination of enzyme activities, substrate-product separation and measurements were carried out in 20 mmol/L sodium borate (pH 10.00) at 25°C on a 42-cm uncoated capillary. Results: Deoxynucleotides and deoxyadenosine were readily detectable in erythrocytes and urine, respectively. Both methods were linear in the range 2-500 μmol/L (r >0.99). Intra- and interassay CV were 0.99 for both). In erythrocytes from healthy individuals, mean (SD) ADA activity was 5619 (2584) nmol/s per liter of packed cells. In erythrocytes of SCID patients at diagnosis, ADA activity was 56.9 (48.3) nmol/s per liter of packed cells; SAHH activity was also much reduced. PNP activity was similar in patients and controls. Conclusions: CE can be used to test ADA deficiency and enables rapid assessment of ADA expression in hematopoietic cells of SCID patients during therapy.