Although this failed clinical trial, which is in contrast to the demonstrated leptin effect in rodents, may be due to many reasons, including potential differences between humans and rodents, one key difference in human T1D patients is that they are always on insulin treatment, and the leptin level is only reduced 50%, compared to non-T1D humans5,44,45, presumably due to the reason that insulin is capable of increasing leptin levels46,47. This evidence concerns the gene INS and type 1 diabetes mellitus.