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Maple Syrup Urine Disease

Information for Physicians and
Other Health Care Providers


Maple syrup urine disease (MSUD) is an inherited disorder of amino acid metabolism, caused by a deficiency in an enzyme complex that results in defects in the catabolism of the amino acids leucine, isoleucine and valine.

Clinical Symptoms

Onset of symptoms can be within the first week of life. Initial signs include poor feeding and vomiting. Additional clinical findings may include lethargy, irritability, muscular rigidity, seizures and eventual metabolic decompensation leading to coma and death. There is a life-long risk for episodes of ketoacidosis, and hypoglycemia is common. Mental and neurological deficits are common findings among individuals with MSUD, especially in patients diagnosed after symptoms have developed.

Newborn Screening and Definitive Diagnosis

In Illinois, newborn screening for MSUD is performed using tandem mass spectrometry. False positive and false negative results are possible with this screening. Infants with a presumptive positive screening tests require prompt follow-up and, when notified of these results, the clinician should immediately check on the clinical status of the baby and refer the infant to a metabolic disease specialist.


Early diagnosis and prompt treatment can significantly affect prognosis. Individuals with MSUD need a life-long diet restricted in branched-chain amino acids, and supplemented with vitamin B 1 (thiamine). During periods of metabolic decompensation, peritoneal dialysis and/or treatment with intra-venous hyperalimentation without branched-chain amino acids (leucine, isoleucine, valine) may be necessary.


MSUD has an estimated incidence between one in 100,000 to one in 300,000 births.

Inheritance Pattern

MSUD is inherited in an autosomal recessive pattern. As an autosomal recessive disorder, the parents of a child with one of these conditions are unaffected, healthy carriers of the condition, and have one normal gene and one abnormal gene. With each pregnancy, carrier parents have a 25 percent chance of having a child with two copies of the abnormal gene, resulting in MSUD. Carrier parents have a 50 percent chance of having a child who is an unaffected carrier, and a 25 percent chance of having an unaffected, non-carrier child. These risks would hold true for each pregnancy. All siblings of infants diagnosed with MSUD should be tested; and genetic counseling services should be offered to the family.


Decarboxylation of leucine, isoleucine and valine is accomplished by a multi-complex enzymatic system (branched-chain alpha ketoacid dehydrogenase). Deficiency of a component enzyme within this pathway causes accumulation of branched-chain amino acids and ketoacids in body fluids and tissues resulting in the clinical manifestations of MSUD.

Key Points for Parents

Avoid overly alarming the child’s parents if the diagnosis has not yet been confirmed. If the child needs additional testing or diagnostic evaluation, make certain that the parents understand the importance of following the pediatrician’s and/or specialist’s recommendations for additional testing and referrals.

Follow-up After Confirmation of Diagnosis

These guidelines should be followed after a diagnosis of MSUD has been confirmed:

  1. Parents should understand that treatment is lifelong and that compliance with dietary management is imperative to the child’s health, growth and development.

  2. Infants and children with MSUD should have regular follow-up appointments with a metabolic disease specialist.

  3. Long-term management, monitoring and compliance with treatment recommendations are essential to the child’s well-being. A multi-disciplinary approach including the following specialties is recommended: pediatrics, genetics and nutrition. Parents should understand that treatment is not curative and that all morbidity cannot necessarily be prevented.

  4. Genetic counseling services are recommended. A list of genetic counselors and geneticists whose services are available through the Illinois Department of Public Health should be given to the parents if they have not already seen a geneticist.

  5. Provide a list of available support services in the community, such as the local health department, Early Intervention service providers and the University of Illinois at Chicago Division of Specialized Care for Children (DSCC).

  6. For more information about newborn screening in general and about maple syrup urine disease specifically, contact the National Newborn Screening and Genetics Resource Center, 1912 W. Anderson Lane, Suite 210, Austin, TX 78757; telephone 512-454-6419; fax 512-454-6509. Other resources include: GeneTests and Online Mendelian Inheritance in Man.

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Illinois Department of Public Health
535 West Jefferson Street
Springfield, Illinois 62761
Phone 217-782-4977
Fax 217-782-3987
TTY 800-547-0466
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