The advent of viral therapy brought concerns about its safety when retroviral integration causing activation of the proto-oncogene LMO2 led to leukemia in patients treated for SCID [78] and after the death of a patient with ornithine transcarbamylase deficiency treated with adenoviral gene therapy [79, 80]. The gene discussed is OTC; the disease is hyperinsulinemic hypoglycemia, familial, 4.