ACADVL and mitochondrial trifunctional protein deficiency: Enzyme assays using lymphocytes to test for CPT-I deficiency and trifunctional protein (TFP) deficiency/long-chain hydroxyacyl-CoA dehydrogenase (LCAHD) deficiency have been reported from the limited laboratories [11], despite our recent development of enzyme assays for CPT-II, very long-chain acyl-CoA dehydrogenase (VLCAD), and medium long-chain acyl-CoA dehydrogenase (MCAD) using lymphocytes [1, 7, 12].