ACAD8 and metabolic disease: Since the first patient with isobutyryl-CoA dehydrogenase deficiency was diagnosed only over a decade ago [21], and since there is substantial variation in the clinical presentation of this deficiency, it also poses the opportunity to investigate other biochemical effects involved in the pathology of deficient isobutyryl-CoA dehydrogenase, as the elucidation of the development of phenotypic characteristics of metabolic diseases remains a formidable challenge.