RAB18 and obesity due to melanocortin 4 receptor deficiency: Using an in vitro model of hyperglycemia/hyperinsulinemia, which induces obesity-associated insulin resistance in 3T3-L1 adipocytes, we recently showed that these conditions significantly reduced Rab18 binding to adipocyte LDs, thus indicating that high concentrations of glucose and insulin, such as those occurring in obesity, prevent Rab18 trafficking to LDs [9].