These are present in some quantity in almost all kinds of food, but in particular, protein-rich foods such as dairy products, meat, fish, soy, gluten, eggs, nuts, whole grains, seeds, avocados, algae, edible seaweed, beans, and pulses. Mutation in any of these genes reduces or eliminates the function of the enzyme complex, preventing the normal breakdown of isoleucine, leucine, and valine. As a result, these amino acids and their by-products build up in the body. Because high levels of these substances are toxic to the brain and other organs, this accumulation leads to the serious medical problems associated with maple syrup urine disease.This condition has an autosomal recessive inheritance pattern, which means the defective gene is located on an autosome, and two copies of the gene – one from each parent – must be inherited to be affected by the disorder. The parents of a child with an autosomal recessive disorder are carriers of one copy of the defective gene, but are usually not affected by the disorder. Pathophysiology
MSUD is a metabolic disorder caused by a deficiency of the branched-chain alpha-keto acid dehydrogenase complex (BCKAD), leading to a buildup of the branched-chain amino acids (leucine, isoleucine, and valine) and their toxic by-products (ketoacids) in the blood and urine. The buildup of these BCAAS will lead to the maple syrup odor that is associated with MSUD. The BCKAD complex begins by breaking down leucine, isoleucine, and valine through the use of branch-chain aminotransferase into their relevant α-ketoacids.
Without sufficient calories, catabolism of muscle protein will result in metabolic crisis. Those with MSUD must be hospitalised for intravenous infusion of sugars and nasogastric drip-feeding of formula, in the event of metabolic decompensation, or lack of appetite, diarrhea or vomiting. Food avoidance, rejection of formula and picky eating are all common problems with MSUD. Some patients may need to receive all or part of their daily nutrition through a feeding tube. Toxin removal
Following diagnosis, rapid removal of excess leucine from the body reduces the impact of the disease on development. Exchange transfusion, hemodialysis, or hemofiltration may be used. Diet control
A diet with carefully controlled levels of the amino acids leucine, isoleucine, and valine must be maintained at all times in order to prevent neurological damage. Since these three amino acids occur in all natural protein, and most natural foods contain some protein, any food intake must be closely monitored, and day-to-day protein intake calculated on a cumulative basis, to ensure individual tolerance levels are not exceeded at any time. As the MSUD diet is so protein-restricted, and adequate protein is a requirement for all humans, tailored metabolic formula containing all the other essential amino acids, as well as any vitamins, minerals, omega-3 fatty acids and trace elements (which may be lacking due to the limited range of permissible foods), are an essential aspect of MSUD management. These complement the MSUD patients natural food intake to meet normal nutritional requirements without causing harm.