Homozygous or compound heterozygous mutations in the ACADVL gene (OMIM #609575) cause a metabolic myopathy due to very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency, an enzyme associated with the inner mitochondrial membrane that plays an important role in the first step of mitochondrial long chain fatty acid oxidation. This evidence concerns the gene ACADVL and very long chain acyl-CoA dehydrogenase deficiency.