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Maple syrup urine disease



Maple syrup urine disease (MSUD) is a disorder in which the body cannot break down certain parts of proteins. The urine of people with this condition can smell like maple syrup.



Maple syrup urine disease (MSUD) is inherited, which means it is passed down through families. It is caused by a defect in 1 of 3 genes. People with this condition cannot break down the 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).

Some types of MSUD are mild or come and go. Even in the mildest form, repeated periods of physical stress can cause mental disability and high levels of leucine to build up.




Symptoms of this disorder include:

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


Exams and Tests


These tests may be done to check for this disorder:

  • Plasma amino acid test
  • Urine organic acid test
  • Genetic testing

There will be signs of ketosis (buildup of ketones, a by-product of burning fat) and excess acid in the blood (acidosis).




When the condition is diagnosed, and during episodes, treatment involves eating a protein-free diet. Fluids, sugars, and sometimes fats are given through a vein (IV). Dialysis through your belly or a vein can be done to reduce the level of abnormal substances in your blood.

Long-term treatment requires a special diet. For infants, the diet includes a formula with low levels of the amino acids leucine, isoleucine, and valine. People with this condition must remain on a diet low in these amino acids for life.

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 parents of children with the condition.


Outlook (Prognosis)


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 adulthood and can remain healthy.


Possible Complications


These complications can occur:

  • Neurological damage
  • Coma
  • Death
  • Mental disability


When to Contact a Medical Professional


Call your health care provider if you have a family history of MSUD and are planning to start a family. Also call your provider right away 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 testing 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.




Enns GM, Cowan TM, Klein O, Packman S. Aminoacidemias and organic acidemias. In: Swaiman K, Ashwal S, Ferriero DM, Ferriero D, eds. Swaiman's Pediatric Neurology: Principles and Practice . 5th ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 32.

Ogier de Baulny H, Dionisi-Vici C, Wendel U. Branched-chain organic acidurias/acidemias. In: Saudubray J-M, van den Berghe G, Walter JH, eds. Inborn Metabolic Diseases: Diagnosis and Treatment . 5th ed. New York, NY: Springer; 2012:chap 19.


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            Review Date: 4/20/2015

            Reviewed By: Chad Haldeman-Englert, MD, FACMG, Wake Forest School of Medicine, Department of Pediatrics, Section on Medical Genetics, Winston-Salem, NC. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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