NOS3 and hyperinsulinemic hypoglycemia, familial, 4: Further to observations in the eNOS–/– ApoE–/– mouse, where endothelial cell dysfunction is attributed to loss of eNOS and hence NO production,32 we now show that preservation of eNOS, but selective loss of NO generation due to BH4 deficiency is associated with increased endothelial cell superoxide and ROS generation.