Maple syrup urine disease (MSUD) is a metabolism disorder passed down through families in which the body cannot break down certain parts of proteins. Urine in persons with this condition can smell like maple syrup.

Maple syrup urine disease (MSUD) is caused by a gene defect. Persons with this condition cannot break down the branched-chain amino acids leucine, isoleucine, and valine. This leads to a buildup 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).

MSUD also occurs in an intermittent form and a mild form. Even in the mildest form, repeated periods of physical stress can cause mental retardation and high levels of leucine.

• Avoiding food
• Coma
• Feeding difficulties
• Lethargy
• Seizures
• Urine that smells like maple syrup
• Vomiting

• Plasma amino acid test
• Urine amino acid test

There will be signs of ketosis and excess acid in blood (acidosis).

When the condition is diagnosed, and during episodes, treatment involves eating a protein-free diet. Fluids, sugars, and possibly fats are given through a vein (IV). Peritoneal dialysis or hemodialysis can be used to reduce the level of amino acids.

A special diet free of branched-chain amino acids is started when amino acid levels are normal. The health care provider will follow these levels closely, and will adjust the diet based on amino acid levels.

Long term treatment requires a special diet. The diet includes a man-made infant formula with low levels of the amino acids leucine, isoleucine, and valine. Persons with this condition must remain on this diet permanently.

It is very important to always follow this diet to prevent nervous system (neurological) damage. This requires frequent blood tests and close supervision by a registered dietitian and physician, as well as cooperation by the parents.

This disease can be life threatening if untreated.

Even with dietary treatment, stressful situations and illness can still cause high levels of certain amino acids. Death may occur during these episodes. With strict dietary treatment, children have grown into healthy adulthood.

• Coma
• Death
• Neurological damage

Call your health care provider if you have a family history of MSUD and are planning to start a family. Also call immediately if you have a newborn who has symptoms of maple syrup urine disease.

Genetic counseling is suggested for people who want to have children and who have a family history of maple syrup urine disease. Many states now screen all newborns with blood tests for MSUD.

If a screening test shows that your baby may have MSUD, a follow-up blood test for amino acid levels should be done right away to confirm the disease.

Wendel U, Ogier de Baulny H. Branched-chain organic acidurias/acidemias. In: Fernandes J, Saudubray J-m, van den Berghe G, Walter JH, eds. Inborn Metabolic Diseases: Diagnosis and Treatment. 4th ed. New York, NY: Springer; 2006:chap 19.