Deficiency of adenosine deaminase type 2 (DADA2) is an autosomal recessive monogenic AID caused by ADA2 (formerly known as CECR1) mutations and was first described in 2014 in patients with mild immune deficiency, systemic inflammation, and central nervous system vasculopathy (20). Here, ADA2 is linked to hyperinsulinemic hypoglycemia, familial, 4.