Maple syrup urine disease (MSUD) is caused by the inability to metabolize the branched-chain amino acids leucine, isoleucine, and valine. The disease is called MSUD because urine from affected people smells like maple syrup.

In the most severe form, MSUD causes severe acidosis during the first week of life. This is characterized by progressively poorer feeding, vomiting, seizures, lethargy, and finally coma.

Untreated infants may die in the first few weeks of life in severe forms of the disease. MSUD also occurs in an intermittent form and a mild form. Even in the mildest form, infections can cause mental retardation and bouts of acidosis.

• Family history of MSUD or unexplained infant death
• Urine which smells like maple syrup
• Feeding difficulties
• Lethargy
• Vomiting
• Seizures
• Coma
• Avoiding food

• Urine amino acids (elevated levels of the amino acids leucine, isoleucine, and valine)
• Plasma amino acids (elevated levels of leucine, isoleucine, and valine)
• Ketosis (elevated levels of ketone bodies in urine and plasma)
• Acidosis (excess acid in blood)

• Acute acidosis is treated to restore normal pH.
• Because this is a protein intolerance disease, protein is cut from the diet .
• High doses of intravenous fluid, sugar and fat are given to prevent dehydration and provide energy to stimulate protein synthesis, which lowers the levels of the amino acids which cannot be broken down.
• Peritoneal dialysis or hemodialysis are used to remove the high levels of amino acids.
• A special diet free of branched-chain amino acids is started immediately.

Long range treatment requires a special diet. Strict compliance is necessary to prevent neurological damage. This requires close supervision by a registered dietitian and a physician, and parental cooperation. The diet includes a synthetic infant formula with low levels of the amino acids leucine, isoleucine, and valine.

Frequent blood testing for amino acid levels allows doctors and dieticians to adjust the balance of these branched-chain amino acids so that they are neither deficient nor in excess. Affected people must remain on this diet permanently.

• Neurological damage such as low IQ, if poorly treated
• Possibly fatal acidosis episodes