The adult forms of CPTII and VLCAD deficiencies are very rare diseases. Twenty-five patients with CPTII deficiency and 15 patients with the myopathic form of VLCAD deficiency are currently followed in our two groups. In case that we can't include enough patients from Denmark and France, we will include patients from our collaborators in the Netherlands and Sweden. All studies will be conducted at Rigshospitalet and Pitié-Salpêtrière Hospital. Only the regularly blood samples will be outsourced to other hospitals, but the results will be faxed or mailed directly to the sponsor or investigators.