Maple syrup urine disease: treatment of the acutely ill newborn

Animal models of maple syrup urine disease

Maple syrup urine disease (MSUD) is an inherited aminoacidopathy resulting from dysfunction of the branched-chain keto acid dehydrogenase (BCKDH) complex. This disease is currently treated primarily by dietary restriction of branched-chain amino acids (BCAAs). However, dietary compliance is often challenging. Conversely, liver transplantation significantly improves outcomes, but donor organs are scarce and there are high costs and potential risks associated with this invasive procedure. Therefore, improved treatment options for MSUD are needed. Development of novel treatments could be facilitated by animal models that accurately mimic the human disease. Animal models provide a useful system in which to explore disease mechanisms and new preclinical therapies. Here we review MSUD and currently available animal models and their corresponding relevance to the human disorder. Using animal models to gain a more complete understanding of the pathophysiology behind the human disease may lead to new or improved therapies to treat or potentially cure the disorder.

Hudson memorial lecture. Neonatal management of organic acidurias. Clinical update

Therapeutic guidelines have been obtained from a retrospective review of 41 patients affected with organic acidaemias, 16 patients with neonatal maple syrup urine disease (MSUD), 11 methylmalonic acidaemia, (MMA) seven propionic acidaemias (PA) and seven isovaleric acidaemias (IVA), and by comparing this personal series with similar reported cases. The emergency treatment of these organic acidurias in the neonate has to main goals: toxin removal and anabolism. Anabolism is always promoted by early diet therapy. The best method of toxin removal depends on the nature of the defect; peritoneal dialysis with exchange transfusions or multiple or prolonged exchange transfusions in MSUD and in PA, diuresis and exchange transfusions in MMA and glycine supplementation in IVA. Vitamin supplementation (thiamine 20 mg, biotin 10 mg, B12 2 mg and riboflavin 100 mg) should be tried in all cases although the neonatal forms of these defects are very rarely vitamin responsive. Additional treatments such as carnitine or insulin may prove to be useful.

Maple syrup urine disease--therapeutic use of insulin in catabolic states

High and neurotoxic blood levels of leucine and its ketoanalogue develop in catabolic patients with maple syrup urine disease. The use of relatively high doses of insulin and additional glucose had a more pronounced effect on lowering leucine (and alpha-ketoisocaproate) blood levels than dietary elimination of leucine alone. This is demonstrated in 2 neonates after blood exchange transfusion and in one 4-months old patient suffering from febrile diarrhea.

Exchange transfusion in acute episodes of maple syrup urine disease. Studies on branched-chain amino and keto acids

Two neonates with maple syrup urine disease were treated by exchange transfusion. Within 15 h blood leucine and KICA concentrations were lowered from 2.6 mM to 1.1 mM using 570 to 620 ml blood per kg body weight. The other branched-chain amino acid/keto acid pairs fell to normal. During exchange transfusion the patient's nitrogen balance seems to be negative. Further exchange transfusion was useless. More importantly the patient should be forced into an anabolic state by high caloric supply or insulin plus glucose treatment. More KICA than leucine was eliminated, however, KICA blood levels remained slightly higher than that of leucine indicating different leucine/KICA equilibria in extravascular compartments than in blood. In a given time interval exchange transfusion was more effective than peritoneal dialysis, probably due to a lack of an additional (peritoneal) membrane. Renal excretion of branched-chain amino and keto acids was very inefficient. The allegedly most toxic metabolite, KICA, had the lowest renal clearance of the branched-chain keto acids.