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Genetic and Rare Diseases Information Center (GARD)

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Maple syrup urine disease

Other Names for this Disease
  • BCKD deficiency
  • Branched chain ketoaciduria
  • Branched-chain alpha-keto acid dehydrogenase deficiency
  • Keto acid decarboxylase deficiency
  • MSUD
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Your Question

I recently began having a maple syrup smell. Is it possible for an adult to develop maple syrup urine disease? How can I get tested?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is maple syrup urine disease?

Maple syrup urine disease is an inherited disorder in which the body is unable to process certain protein building blocks (amino acids) properly. Beginning in early infancy, this condition is characterized by poor feeding, vomiting, lack of energy (lethargy), seizures, and developmental delay. The urine of affected infants has a distinctive sweet odor, much like burned caramel, that gives the condition its name. Maple syrup urine disease can be life-threatening if untreated.[1]
Last updated: 5/10/2012

Are there different types of maple syrup urine disease?

There are four general types of maple syrup urine disease. The different types are classified based on the amount and type of enzyme activity present in the affected individual.[2]

  • Classic maple syrup urine disease is the most common type. Individuals with classic maple syrup urine disease have little or no enzyme activity (usually less than 2 % of normal). Infants with this type of maple syrup urine disease will show symptoms within the first several days of life. It is managed through diet with severe protein restriction.
  • Intermediate maple syrup urine disease is a variant of the classic type. Individuals with intermediate maple syrup urine disease have a higher level of enzyme activity (approximately 3 to 8% of normal) and can tolerate a greater amount of leucine. However, in periods of illness or fasting, these individuals may react like a child with the classic type of maple syrup urine disease. Management is similar to that used for the classic type.
  • Intermittent maple syrup urine disease is a milder form of the disease. Individuals with this type have a greater level of enzyme activity (approximately 8 to 15% of normal) and often do not have symptoms until 12 to 24 months of age, usually as a result of an illness or surge in protein intake. During an illness, an individual with intermittent maple syrup urine disease may exhibit a strong maple syrup odor and/or go into a metabolic crisis.
  • Thiamine-responsive maple syrup urine disease is so named because large doses of thiamine given to these individuals will result in an increase in the enzyme activity which breaks down leucine, isoleucine and valine. Only moderate protein restriction is needed to manage this type of maple syrup urine disease.  
Last updated: 5/10/2012

Is it possible for an adult to develop maple syrup urine disease?

At times a peculiar maple syrup smell in the urine or sweat can occur in older, healthy children or adults who are non-symptomatic. The reason for this is unknown. However, these individuals should be checked for a milder form of maple syrup urine disease, especially if there are other symptoms suggestive of maple syrup urine disease.[3]
Last updated: 5/10/2012

How can I get tested for maple syrup urine disease?

GeneTests lists laboratories offering clinical genetic testing for maple syrup urine disease. Clinical genetic tests are ordered to help diagnose a person or family and to aid in decisions regarding medical care or reproductive issues. Talk to your health care provider or a genetic professional to learn more about your testing options.
Last updated: 5/10/2012

How can I find a genetics professional in my area?

Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.

The following online resources can help you find a genetics professional in your community:  

  • GeneTests has a searchable directory of US and international genetics and prenatal diagnosis clinics.
  • The National Society of Genetic Counselors provides a searchable directory of US and international genetic counseling services.
  • The American College of Medical Genetics has a searchable database of US genetics clinics.  
  • The American Society of Human Genetics maintains a database of its members, which includes individuals who live outside of the United States. Visit the link to obtain a list of the geneticists in your country, some of whom may be researchers that do not provide medical care.
Last updated: 12/13/2012