RBP4 and obesity due to melanocortin 4 receptor deficiency: Moreover, long-term treatment with fenretinide for several months prevented high-fat diet induced obesity, insulin resistance, and hepatic steatosis, whereas, unexpectedly, some of these beneficial effects were also observed in mice lacking RBP4 (Preitner et al., 2009), proposing also RBP4-independent mechanisms at play.