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Disease Profile

3-methylcrotonyl-CoA carboxylase deficiency

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.


US Estimated

Europe Estimated

Age of onset

All ages





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)

3MCC; 3-MCC deficiency; 3-methylcrotonylglycinuria;


Congenital and Genetic Diseases; Metabolic disorders; Newborn Screening


3-methylcrotonyl-CoA carboxylase deficiency (3-MCC deficiency) is an inherited condition in which the body is unable to breakdown the amino acid, leucine (a building block of protein). Some children with 3-MCC deficiency will begin developing signs and symptoms during infancy or early childhood; however, more recent studies suggest that many affected babies identified through newborn screening will never experience symptoms of the condition.[1] 3-MCC deficiency may be associated with episodes of "metabolic crisis" in which affected people experience poor appetite, lack of energy, irritability, weakness, nausea and/or vomiting. If metabolic crises are untreated, the condition can lead to developmental delay, seizures, coma, and even death. 3-MCC deficiency is caused by changes (mutations) in MCCC1 or MCCC2 gene and is inherited in an autosomal recessive manner. Treatment may include a low-leucine diet and appropriate supplements.[2]


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
Abnormal circulating leucine concentration
Low blood sugar
Muscular hypotonia
Low or weak muscle tone
Organic aciduria
30%-79% of people have these symptoms
Abnormality of movement
Movement disorder
Unusual movement

[ more ]

Failure to thrive in infancy
Faltering weight in infancy
Weight faltering in infancy

[ more ]

High blood ammonia levels
5%-29% of people have these symptoms
Abnormality of the cerebral vasculature
Abnormality of the cerebral blood vessels
Respiratory insufficiency
Respiratory impairment
Involuntary muscle stiffness, contraction, or spasm


Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

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.
  • Orphanet lists international laboratories offering diagnostic testing for this condition.

    Newborn Screening

    • 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.


      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 Genetics contains information on 3-methylcrotonyl-CoA carboxylase deficiency. This website is maintained by the National Library of Medicine.
        • 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

          • 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 3-methylcrotonyl-CoA carboxylase deficiency for health care professionals.
          • Online Mendelian Inheritance in Man (OMIM) lists the subtypes and associated genes for 3-methylcrotonyl-CoA carboxylase deficiency in a table called Phenotypic Series. Each entry in OMIM includes 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 3-methylcrotonyl-CoA carboxylase deficiency. Click on the link to view a sample search on this topic.


            1. Rips J, Almashanu S, Mandel H, Josephsberg S, Lerman-Sagie T, Zerem A, Podeh B, Anikster Y, Shaag A, Luder A, Staretz Chacham O, Spiegel R. Primary and maternal 3-methylcrotonyl-CoA carboxylase deficiency: insights from the Israel newborn screening program. J Inherit Metab Dis. March 2016; 39(2):211-217. https://www.ncbi.nlm.nih.gov/pubmed/26566957.
            2. 3-methylcrotonyl CoA carboxylase deficiency. STAR-G. August 2013; https://www.newbornscreening.info/Parents/organicaciddisorders/3MCC.html.