INS and obesity due to melanocortin 4 receptor deficiency: AAV mediated gene delivery methods are considered safe and have high gene delivery efficacy and are therefore promising tools for gene therapy.37 In adult mice, the same AAV8‐BMP4 vector as used here was shown to increase insulin sensitivity and protected mice on a high‐fat diet from obesity.22 In line with this study,22 we found that while control mice had a weight gain of about 5% in the 8 weeks from viral injections until culling, the weight of BMP4 treated mice remained unchanged during the course of the study.