Vogel et al. Orphanet Journal of Rare Diseases 2014, 9:73

Full list of author information is available at the end of the articleMaple syrup urine disease (MSUD; branched chain ketoa-cid dehydrogenase (BCKDH) deficiency) and phenylketon-uria (PKU) comprise the large neutral aminoacidopathies. Untreated MSUD results in accumulation of the branched-chain amino acids (BCAAs) leucine (LEU), valine (VAL) and isoleucine (ILE) [1-4]. Additionally, induction of increase the BCAA’s corresponding α-keto acids (BCKAs), including α-ketoisocaproate (KIC, from LEU), α-keto-β-methylvalerate (KMV, from ILE) and α-ketoisovalerate (KIV, from VAL), all of which can freely traverse the blood–brain barrier (BBB) and transaminate to yield the corresponding BCAAs [5]. Treatment of MSUD requires strict protein restriction combined with BCAA supplementation to levels compatible with adequate development and growth. Although dietary interventio