Enzyme activity in dried blood spot as a diagnostic tool for adenosine deaminase 2 deficiency

Background Deficiency of adenosine deaminase 2 (DADA2) is an autoinflammatory disease caused by mutations in the adenosine deaminase 2 (ADA2) gene. Loss of functional ADA2 activity results in vasculitis syndrome, immunodeficiency, and hematopoietic disorders. Early diagnosis is required for effective treatment. Methods We developed a dried blood spot (DBS)-based ADA2 activity colorimetric assay. Heparin-affinity purification was used during sample preparation to improve the assay more efficiently. The stability of ADA2 during DBS storage and ADA2 activity of DADA2 patients and healthy controls were examined. Results Active ADA2 was extracted from the DBS of healthy controls. ADA2 activity in DBS, stored either frozen or refrigerated, remained stable for at least 90 days. A significant difference in ADA2 activity was observed between healthy controls and patients. No ADA2 activity was detected in DBS from patients. Conclusions Our new DBS ADA2 activity assay is experimentally simple, highly adaptable, and requires no special equipment except for a microplate reader. A low background was achieved with heparin-affinity purification. The method differentiates clearly between healthy controls and patients. ADA2 activity can be reliably measured in DBS, providing an opportunity to diagnose DADA2 at an early stage.