Complete histopathologic examination of one group of mutant and MCAD+/+ control mice after a 24-h fast demonstrated diffuse microvesicular and macrovesicular hepatic steatosis in 6–8-wk-old MCAD−/− mice whereas MCAD+/+ mice had no histologic changes (Figure 5A and 5B). In another group of 4-wk-old MCAD+/+ and MCAD−/− mice fasted for 24-h, there were minimal to no abnormalities in all organs evaluated. Only the older MCAD−/− mice, therefore, demonstrated hepatic steatosis. In addition, we found sporadic cardiac lesions in multiple MCAD−/− mice.