Interestingly, in mouse hepatocytes TBC1D1 localises to insulin-like growth factor 1 (IGF1)-containing storage vesicles, and a TBC1D1 S231A (equivalent to Ser237 in humans) knock-in mutation promotes increased IGF1 secretion from the liver, leading to lipogenic gene expression in adipose tissue and consequent obesity [19]. Here, IGF1 is linked to obesity due to melanocortin 4 receptor deficiency.