SIM1 and obesity due to melanocortin 4 receptor deficiency: The obesity phenotype with MYT1L loss of function is associated with disrupted development of the neuroendocrine hypothalamus in zebrafish, manifested by loss of OXT. This is similar to the effects of SIM1 [8, 9] and POU3F2 loss of function [24], both of which are associated with hyperphagic obesity.