Background: The deficiency of adenosine deaminase 2 (DADA2) is an autosomal recessively inherited disease resulting from loss‐of‐function mutations in ADA2, formerly named CECR1 (cat eye syndrome chromosome region, candidate 1) gene. Disease manifestations could be separated into three major phenotypes: inflammatory/vascular, immune dysregulatory, and hematologic; however, most patients presented with significant overlap between these three phenotype groups. Case Presentation: We present a case of DADA2 deficiency with disease onset at 3 years old, not recognized till the age of 18 with severe gastrointestinal vasculitis and recurrent episodes of neutropenia associated with a new CECR1 mutation. [ABSTRACT FROM AUTHOR]