We analyzed PBMCS from five patients with FAO disorders; one with a mutation in the CPT1A gene (OMIM 600528, causing CPT1α deficiency), two with mutations in CPT2 gene (OMIM 600650), and two with mutations in HADHA, one of the two genes encoding for the mitochondrial trifunctional protein (MTP) (OMIM 600890, causing MTP deficiency). The gene discussed is HADHA; the disease is abetalipoproteinemia.