AbstractA protein altering variant in the gene encoding zinc finger homeobox-3 (ZFHX3) has recently been associated with lower BMI in a human genome-wide association study. We investigated metabolic parameters in mice harbouring a missense mutation inZfhx3(Zfhx3Sci/+) and looked for alteredin situexpression of transcripts that are associated with energy balance in the hypothalamus to understand how ZFHX3 may influence growth and metabolic effects. One year old male and femaleZfhx3Sci/+mice weighed less, had shorter body length, reduced fat mass, smaller mesenteric fat depots, and lower circulating insulin, leptin, and insulin-like growth factor-1 (IGF1) concentrations thanZfhx3+/+littermates. In a second cohort of 9 – 20-week-old males and females,Zfhx3Sci/+mice ate less than wildtype controls, in proportion to body weight. In a third cohort of female-onlyZfhx3Sci/+andZfhx3+/+mice that underwent metabolic phenotyping from 6 - 14 weeks old,Zfhx3Sci/+mice weighed less and had lower lean mass and energy expenditure, but fat mass didn’t differ. We detected increased expression of somatostatin, and decreased expression of growth hormone-releasing hormone and growth hormone-receptor mRNAs in the arcuate nucleus (ARC). Similarly, ARC expression of orexigenic neuropeptide Y was decreased and ventricular ependymal expression of orphan G protein-coupled receptorGpr50was decreased. We demonstrate for the first time an energy balance effect of theZfhx3Scimutation, likely by altering expression of key ARC neuropeptides to alter growth, food intake and energy expenditure.