Since these initial studies, systemic delivery of LVs has been considered for a number of monogenic diseases, including the coagulation deficiencies hemophilia A2 and hemophilia B,3 inborn errors of metabolism such as lysosomal storage disorders MPS1,4 MPS3a,5 MPS3b,6 bilirubin-UDP-glucuronosyltransferase deficiency (Crigler-Najjar),7 Pompe disease,8 and adenosine deaminase (ADA) deficiency,9 among others. The gene discussed is ADA; the disease is hyperinsulinemic hypoglycemia, familial, 4.