Complement studies then revealed persistently low C4 with normal C3, a biochemical pattern regarded as characteristic of C1-INH deficiency and recommended by the World Allergy Organization/European Academy of Allergy and Clinical Immunology (WAO/EAACI) guideline as the initial screening clue before measuring C1-INH concentration and function [7,8]. The gene discussed is C3; the disease is hyperinsulinemic hypoglycemia, familial, 4.