Maple syrup in urine disease is an inheritable metabolic disease of amino acid metabolism characterized by acidosis , central nervous system symptoms, and urine that may smell sweet like maple syrup.

Alternative Names

MSUD

Causes, incidence, and risk factors

Maple syrup urine disease (MSUD) is caused by the inability to metabolize the so-called '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, MSUD results in mental retardation and bouts of acidosis precipitated by stresses such as ordinary infections.

Signs and tests

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 leves of ketone bodies in urine and plasma

Acidosis = excess acid in blood

Treatment

Treatment of the acute episode:

Acute

acidosis is treated to restore normal pH.

Stop protein in diet as this is a protein intolerance disease.

High levels of intravenous fluid, sugar and fat are important 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

can be used to remove the high levels of

amino acids .

Prompt institution of a special diet that is free of branch chain amino acids.

Long range treatment: Treatment includes a special diet. Strict compliance is necessary to prevent neurological damage. This requires close supervision by a registered dietitian or physician, and cooperation by parent(s). The diet includes a synthetic infant formula with low levels of the amino acids leucine, isoleucine, and valine. Frequent blood testing of amino acids allows doctors/dieticians to adjust the balance of these branch chain amino acids so that they are neither deficient nor in excess. Affected people must remain on this diet permanently.

Expectations (prognosis)

If left untreated, life-threatening neurological damage may result. Despite dietary treatment, stressful situations can still precipitate bouts of acidosis and death may occur during these episodes. With strict dietary treatment, children have grown up healthy and able to attend college.

Complications

Neurological damage, for example lower IQ if poorly treated

Acidosis

episodes (may be fatal)

Calling your health care provider

Call your health care provider if you have a family history of MSUD and are contemplating starting a family. Also call immediately if you have a newborn who exhibits symptoms suggestive of maple syrup urine disease.

Prevention

Genetic counseling is suggested for prospective parents with a family history of maple syrup urine disease. Some states, such as Pennsylvania, screen all newborn babies blood for signs of MSUD. You may receive a call from your pediatrician stating that your baby had an abnormal blood test for MSUD. This may be a 'false positive' test, but a blood test (amino acid levels) should be done right away to tell for certain.