2-Methylbutyryl-CoA dehydrogenase deficiency disorder, also known as short/branched-chain acyl-coA dehydrogenase deficiency, is an inborn error of L-isoleucine catabolism. It is characterized by increased urinary excretion of 2-methylbutyrylglycine (2-MBG), and increased whole blood and plasma concentrations of 2-methylbutyryl (C5) carnitine. The phenotype is not well defined, ranging from completely asymptomatic patients to those with muscle hypotonia, cerebral palsy, developmental delay, lethargy, hypoglycemia, and metabolic acidosis.