Animals with deficiencies in acyl CoA oxidase [44] or short-chain acyl CoA dehydrogenase [45] exhibit spontaneous steatosis, but animals with deficiencies in very long chain acyl CoA dehydrogenase [46], long chain acyl CoA dehydrogenase [42], medium chain acyl CoA dehydrogenase [47], dienoyl CoA reductase [43], enoyl-CoA isomerase [48] and PPARα [49] exhibit steatosis only upon fasting. The gene discussed is ACADS; the disease is steatosis.