NOD2, the most studied NLR in relation to XIAP deficiency, is expressed mainly by cells of haematopoietic origin and by Paneth cells in the gut, and is activated by muramyl dipeptide (MDP), a constituent of Gram-negative and Gram-positive bacteria (41, 42). The gene discussed is XIAP; the disease is hyperinsulinemic hypoglycemia, familial, 4.