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branched chain keto acid dehydrogenase E1 subunit beta

Normal Function

The BCKDHB gene provides instructions for making one part, the beta subunit, of a group of enzymes called the branched-chain alpha-keto acid dehydrogenase (BCKD) enzyme complex. Two beta subunits connect with two alpha subunits, which are produced from the BCKDHA gene, to form a critical piece of the enzyme complex called the E1 component.

The BCKD enzyme complex is responsible for one step in the normal breakdown of three protein building blocks (amino acids). These amino acids—leucine, isoleucine, and valine—are obtained from the diet. They are present in many kinds of food, particularly protein-rich foods such as milk, meat, and eggs. The BCKD enzyme complex is active in mitochondria, which are specialized structures inside cells that serve as energy-producing centers. The breakdown of leucine, isoleucine, and valine produces molecules that can be used for energy.

Health Conditions Related to Genetic Changes

Maple syrup urine disease

More than 90 mutations in the BCKDHB gene have been identified in people with maple syrup urine disease. These mutations most often cause the severe, classic form of the disorder, which becomes apparent soon after birth. Maple syrup urine disease gets its name from the distinctive sweet odor of affected infants' urine. It is also characterized by poor feeding, vomiting, lack of energy (lethargy), abnormal movements, and delayed development.

Most BCKDHB gene mutations change single amino acids in the beta subunit of the BCKD enzyme complex. Other mutations insert or delete small amounts of DNA in the gene. A particular mutation is most common in people of Ashkenazi (eastern and central European) Jewish descent; this mutation replaces the amino acid arginine with the amino acid proline at position 183 in the beta subunit (written as Arg183Pro or R183P).

Mutations in the BCKDHB gene disrupt the normal function of the BCKD enzyme complex, preventing it from effectively breaking down leucine, isoleucine, and valine. As a result, these amino acids and their byproducts build up in the body. This accumulation is toxic to cells and tissues, particularly in the nervous system. The buildup of these substances can lead to seizures, developmental delay, and the other health problems associated with maple syrup urine disease.

More About This Health Condition

Other Names for This Gene

  • 2-oxoisovalerate dehydrogenase beta subunit
  • BCKDH E1-beta
  • branched chain keto acid dehydrogenase E1, beta polypeptide
  • branched chain keto acid dehydrogenase E1, beta polypeptide (maple syrup urine disease)

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Gene and Variant Databases


  • Edelmann L, Wasserstein MP, Kornreich R, Sansaricq C, Snyderman SE, Diaz GA. Maple syrup urine disease: identification and carrier-frequency determination of a novel founder mutation in the Ashkenazi Jewish population. Am J Hum Genet. 2001 Oct;69(4):863-8. doi: 10.1086/323677. Epub 2001 Aug 16. Citation on PubMed or Free article on PubMed Central
  • Flaschker N, Feyen O, Fend S, Simon E, Schadewaldt P, Wendel U. Description of the mutations in 15 subjects with variant forms of maple syrup urine disease. J Inherit Metab Dis. 2007 Nov;30(6):903-9. doi: 10.1007/s10545-007-0579-x. Epub 2007 Oct 8. Citation on PubMed
  • Henneke M, Flaschker N, Helbling C, Muller M, Schadewaldt P, Gartner J, Wendel U. Identification of twelve novel mutations in patients with classic and variant forms of maple syrup urine disease. Hum Mutat. 2003 Nov;22(5):417. doi: 10.1002/humu.9187. Citation on PubMed
  • Nellis MM, Danner DJ. Gene preference in maple syrup urine disease. Am J Hum Genet. 2001 Jan;68(1):232-7. doi: 10.1086/316950. Epub 2000 Dec 7. Citation on PubMed or Free article on PubMed Central
  • Quental S, Macedo-Ribeiro S, Matos R, Vilarinho L, Martins E, Teles EL, Rodrigues E, Diogo L, Garcia P, Eusebio F, Gaspar A, Sequeira S, Furtado F, Lanca I, Amorim A, Prata MJ. Molecular and structural analyses of maple syrup urine disease and identification of a founder mutation in a Portuguese Gypsy community. Mol Genet Metab. 2008 Jun;94(2):148-56. doi: 10.1016/j.ymgme.2008.02.008. Epub 2008 Apr 2. Citation on PubMed
  • Rodriguez-Pombo P, Navarrete R, Merinero B, Gomez-Puertas P, Ugarte M. Mutational spectrum of maple syrup urine disease in Spain. Hum Mutat. 2006 Jul;27(7):715. doi: 10.1002/humu.9428. Citation on PubMed
  • Strauss KA, Puffenberger EG, Carson VJ. Maple Syrup Urine Disease. 2006 Jan 30 [updated 2020 Apr 23]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.