FLAD1 and multiple acyl-CoA dehydrogenase deficiency: The expected central role of FADS in human muscle bioenergetics has been recently proved by the occurrence of certain riboflavin-responsive and non-responsive cases of Multiple Acyl CoA dehydrogenase deficiency (MADD, OMIM 231680) and/or of multiple respiratory-chain deficiency caused by mutations in FLAD1 [30,31].