During a recent literature review on maple syrup urine disease, I came across an older article from 1998 (Suryawan et al. Am J Clin Nutr. 1998;68:72–81.) in which the authors examined branch chain amino acid metabolism (BCAT and BCKD) in various tissues. They found that most of the oxidative capacity was in skeletal muscle and liver (with muscle  representing the greatest proportion of activity)  and that  brain (10-20%) and kidney (8-13%)  also contribute significantly to  BCAA metabolism.

Since the muscle quantitatively has the strongest role in BCAA metabolism, “domino” transplants, in which individuals with MSUD receive liver transplants, and then are able to donate their livers to recipients with other diseases, have been successful (Braz J Med Biol Res. 2014 Jun;47(6):522-6. Epub 2014 Apr 25.)

Hilary Vernon, MD PhD