Detailed Information on Maple Syrup Urine Disease

Maple Syrup Urine Disease (MSUD) is a disorder abnormally affecting the metabolism of amino acids.  The disorder impresses the way the body metabolizes certain components of protein. These components are the three branch-chain amino-acids leucine, isoleucine, and valine. These amino acids accumulate in the blood causing a toxic effect that interferes with brain function. MSUD is caused by a deficiency of the metabolic enzyme branched-chain a-keto acid dehydrogenase (BCKDH), leading to a buildup of the branched-chain amino acids (leucine, isoleucine, and valine) and their toxic by-products in the blood and urine.

The gene defect for MSUD is an autosomal recessive genetic trait and is unknowingly passed down from generation to generation.  This faulty gene usually emerges when two carriers have children together and pass it to their offspring.  For each pregnancy of two such carriers, there is a 25% chance that the child will be born with the disease and a 50% chance the child will be a carrier for the gene defect. Persons with this condition cannot break down the branched-chain amino acids leucine, isoleucine, and valine.

This leads to a build-up of these chemicals in the blood. In the most severe form, MSUD can damage the brain during times of physical stress (such as infection, fever, or not eating for a long time). The symptoms of maple syrup urine disease involve poor feeding, vomiting, dehydration, lethargy, hypotonia, seizures, ketoacidosis, and neurological decline. The two main aspects to the treatment of maple syrup urine disease (MSUD) are long-term management and the treatment of episodes of acute metabolic decompensation. Peritoneal dialysis or hemodialyses are used to reduce the level of amino acids.

Long term treatment requires a special diet. The diet includes a synthetic infant formula with down levels of the amino acids leucine, isoleucine, and valine. The goal of dietary therapy is normalization of branched-chain amino acids (particularly of leucine) by restricting intake of branched-chain amino acids without impairing growth and intellectual development. Dietary therapy must be lifelong. Gene therapy is also a potential future treatment for patients with MSUD. This would involve replacing the mutated gene with a good copy, allowing the patient's cells to generate a functional BCKD protein complex and break down the excess amino acids.