CAT and hyperinsulinemic hypoglycemia, familial, 4: Deficiency of adenosine deaminase 2 (DADA2) is a rare recessive disorder caused by the bi-allelic loss-of-function pathogenic variants in the <i>ADA2</i> gene (MIM: 607575, also known as <i>CECR1</i>, cat eye syndrome chromosome region, candidate 1).