In this study, we focus on two diseases of mitochondrial fatty acid metabolism, i.e., very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) and malonyl-CoA synthetase deficiency (acyl-CoA synthetase family member 3 (ACSF3) deficiency). This evidence concerns the gene ACSF3 and very long chain acyl-CoA dehydrogenase deficiency.