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Disease Profile

Maple syrup urine disease

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.

1-9 / 1 000 000

US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Branched chain ketoaciduria; Branched-chain alpha-keto acid dehydrogenase deficiency; BCKD deficiency;


Newborn Screening


Maple syrup urine disease (MSUD) occurs when the body is unable to breakdown certain parts of proteins. This leads to the build-up of toxic substances that can cause organ and brain damage. There are several forms of MSUD. The most common is the classic or infantile form. Symptoms of the classic form of MSUD start in early infancy and include poor feeding, irritability, extra sleepiness, and muscle spasms. If untreated, respiratory failure (lack of oxygen getting to the blood) may occur. The earwax and urine of infants with MSUD smells like maple syrup. The symptoms of other forms of MSUD start in adolescence or adulthood. MSUD is caused by genetic variants in the BCKDHA, BCKDHB, or DBT genes. It is inherited in an autosomal recessive pattern. Diagnosis of MSUD is based on the symptoms, clinical exam, and blood and urine testing. MSUD is often diagnosed based on the results of a newborn screening test. Treatment includes a special protein restricted diet, supplements, and liver transplantation in some cases.[1][2][3][4]


The following list includes the most common signs and symptoms in people with maple syrup urine disease (MSUD). These features may be different from person to person. Some people may have more symptoms than others, and they can range from mild to severe. This list does not include every symptom that has been described in the condition.

Symptoms of the classic (infantile) form of MSUD that is untreated may include:[1][2]

  • Irritability
  • Extra sleepiness
  • Difficulty feeding
  • Difficulty breathing
  • Muscle spasms of the head, neck, and spine
  • Breathing failure
  • Intellectual and developmental disability
  • Coma

The severity of symptoms depends on the type of MSUD, when treatment is started, and how strictly the treatment recommendations are followed. Without treatment, MSUD can lead to serious complications and death. Early treatment significantly reduces the risk of severe symptoms. Adolescents and adults with MSUD are at risk for attention deficit disorder, anxiety, and depression. Infections, stress, surgeries, and injuries may lead to neurological damage at any age. Treatment by a medical specialist during these episodes is important to limit long-term impairments.

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
80%-99% of people have these symptoms
Abnormality of the pharynx
Abnormality of the voice
Voice abnormality
Elevated plasma branched chain amino acids
Global developmental delay
Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific

[ more ]

Muscular hypotonia
Low or weak muscle tone
Reduced tendon reflexes
Respiratory insufficiency
Respiratory impairment
30%-79% of people have these symptoms
Paralysis or weakness of one side of body
Percent of people who have these symptoms is not available through HPO
Autosomal recessive inheritance
Cerebral edema
Swelling of brain
Elevated circulating L-alloisoleucine concentration
Feeding difficulties in infancy
Generalized hypotonia
Decreased muscle tone
Low muscle tone

[ more ]

Growth abnormality
Abnormal growth
Growth issue

[ more ]

Sensory hallucination

[ more ]

Low blood sugar
High levels of ketone bodies
Lactic acidosis
Increased lactate in body
Pancreatic inflammation
Throwing up


Maple syrup urine disease (MSUD) occurs when either the BCKDHA, BCKDHB, or DBT gene is not working correctly. Variants in another gene, DLD, cause a condition similar to MSUD but with different symptoms.[1][2]

DNA changes known as pathogenic variants are responsible for making genes work incorrectly or sometimes, not at all.


Maple syrup urine disease (MSUD) is often diagnosed based on the results of a newborn screening test. The diagnosis is then confirmed by urine and blood testing. In some cases, especially in adolescents and adults, MSUD is diagnosed based on the symptoms, clinical exam, and the results of urine and blood testing. The results of genetic testing may help confirm the diagnosis.[1][3]

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.

    Newborn Screening

    • An ACTion (ACT) sheet is available for this condition that describes the short-term actions a health professional should follow when an infant has a positive newborn screening result. ACT sheets were developed by experts in collaboration with the American College of Medical Genetics.
    • An Algorithm flowchart is available for this condition for determining the final diagnosis in an infant with a positive newborn screening result. Algorithms are developed by experts in collaboration with the American College of Medical Genetics.
    • Baby's First Test is the nation's newborn screening education center for families and providers. This site provides information and resources about screening at the local, state, and national levels and serves as the Clearinghouse for newborn screening information.
    • The Newborn Screening Coding and Terminology Guide has information on the standard codes used for newborn screening tests. Using these standards helps compare data across different laboratories. This resource was created by the National Library of Medicine.
    • National Newborn Screening and Global Resource Center (NNSGRC) provides information and resources in the area of newborn screening and genetics to benefit health professionals, the public health community, consumers and government officials.


      Treatment for maple syrup urine disease (MSUD) involves a protein-restricted diet and supplements. With early treatment, people with MSUD avoid many of the more severe symptoms. Guidelines exist for medical and diet management of people with MSUD.[1][4][5] 

      Liver transplant is an option in some cases. Liver transplant is considered a cure, although it cannot reverse any neurological damage caused before the transplant was performed.[1]

      Specialists involved in the care of someone with MSUD may include:

      • Medical geneticist
      • Metabolic dieticians
      • Gastroenterologist
      • Neurologist
      • Developmental pediatrician
      • Psychologist/psychiatrist

      Management Guidelines

      • Orphanet Emergency Guidelines is an article which is expert-authored and peer-reviewed that is intended to guide health care professionals in emergency situations involving this condition.


        Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

        Organizations Supporting this Disease

          Learn more

          These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

          Where to Start

          • MedlinePlus was designed by the National Library of Medicine to help you research your health questions, and it provides more information about this topic.
          • MedlinePlus Genetics contains information on Maple syrup urine disease. This website is maintained by the National Library of Medicine.
          • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.
          • The Screening, Technology And Research in Genetics (STAR-G) Project has a fact sheet on this condition, which was written specifically for families that have received a diagnosis as a result of newborn screening. This fact sheet provides general information about the condition and answers questions that are of particular concern to parents.

            In-Depth Information

            • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.
            • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
            • MeSH® (Medical Subject Headings) is a terminology tool used by the National Library of Medicine. Click on the link to view information on this topic.
            • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
            • The New England Consortium of Metabolic Program has written medical guidelines called acute care protocols for Maple syrup urine disease for health care professionals.
            • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
            • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
            • PubMed is a searchable database of medical literature and lists journal articles that discuss Maple syrup urine disease. Click on the link to view a sample search on this topic.


              1. Strauss KA, Puffenberger EG, Carson VJ. Maple Syrup Urine Disease. GeneReviews. Updated Apr 23, 2020; https://www.ncbi.nlm.nih.gov/books/NBK1319/.
              2. Hassan SA, Gupta V. Maple Syrup Urine Disease. StatPearls. Oct 5, 2020; https://pubmed.ncbi.nlm.nih.gov/32491705/.
              3. Blackburn PR, Gass JM, Vairo FPE, Farnham KM, Atwal HK, et al. Maple syrup urine disease: mechanisms and management. Appl Clin Genet. Sep 6, 2017; 10:57-66. https://pubmed.ncbi.nlm.nih.gov/28919799/.
              4. Strauss KA, Carson VJ, Soltys K, Young ME, Bowser LE, Puffenberger EG et al. Branched-chain a-ketoacid dehydrogenase deficiency (maple syrup urine disease): Treatment, biomarkers, and outcomes. Mol Genet Metab. Mar 2020; 129(3):193-206. https://pubmed.ncbi.nlm.nih.gov/31980395/.
              5. Frazier DM, Allgeier C, Homer C, Marriage BJ, et al. Nutrition management guideline for maple syrup urine disease: An evidenceand consensus-based approach. Molecular Genetics and Metabolism. 2014; 112:3:210-217. https://pubmed.ncbi.nlm.nih.gov/24881969/.

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