Defects or absences of the enzyme medium-chain acyl-CoA dehydrogenase, as in MCADD, lead to the accumulation of medium fatty acyl-CoAs in the mitochondria matrix, which subsequently binds to the mitochondrial carnitine molecules, resulting in the formation of medium acylcarnitines. The gene discussed is ACADM; the disease is medium chain acyl-CoA dehydrogenase deficiency.