Several obesity- and lipid-metabolism-related genes were differentially expressed in the testis of obese rats, including fatty acid synthesis, such as acyl-CoA thioesterase 4 (O/C −10.75) or fatty acid elongation, including 3-hydroxyacyl-CoA dehydratase 4 (O/C 4.81). The gene discussed is ACOT4; the disease is obesity due to melanocortin 4 receptor deficiency.