Other genes that located outside of the MHC region, such as MAD1L1, RERE, SORCS3 and ANKK1, are associated with neuronal development and guidance of neuronal growth [58], transcriptional processes [59, 60] and other risk factors for depression, for example, obesity, smoking and abnormal physical development [61]. This evidence concerns the gene RERE and obesity due to melanocortin 4 receptor deficiency.