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BCKDHB gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

BCKDHB gene

The BCKDHB gene is essential for producing the beta subunit of the BCKD enzyme complex, which is required to process specific amino acids for cellular energy.

Normal Function

The BCKDHB gene provides instructions for making the beta subunit of the branched-chain alpha-keto acid dehydrogenase (BCKD) enzyme complex. Two beta subunits pair with two alpha subunits (produced from the BCKDHA gene) to form the E1 component of the enzyme complex.

The BCKD enzyme complex functions within mitochondria to break down three dietary amino acids: leucine, isoleucine, and valine. This process is vital for converting these protein building blocks into molecules that the body uses for energy.

Health Conditions Related to Genetic Changes

Maple syrup urine disease

Over 90 mutations in the BCKDHB gene have been linked to maple syrup urine disease. These mutations often result in the severe, classic form of the disorder.

  • Symptoms: Affected infants may exhibit poor feeding, vomiting, lethargy, abnormal movements, delayed development, and urine that has a characteristic sweet odor.
  • Mechanism: Mutations in the BCKDHB gene prevent the BCKD enzyme complex from breaking down leucine, isoleucine, and valine. The buildup of these amino acids and their byproducts is toxic to the nervous system, causing seizures and developmental issues.
  • Specific Mutations: Mutations may involve single amino acid changes or small insertions/deletions of DNA. A common mutation in the Ashkenazi Jewish population replaces arginine with proline at position 183 (Arg183Pro or R183P).

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)
  • ODBB_HUMAN

Frequently Asked Questions

Maple syrup urine disease linked to the BCKDHB gene is inherited in an autosomal recessive pattern. This means an affected child must inherit one altered copy of the gene from each parent. Parents are typically asymptomatic carriers with one functional gene copy. Genetic counseling and carrier screening are strongly recommended for reproductive partners and extended family members, particularly within higher-risk groups such as individuals of Ashkenazi Jewish ancestry where the Arg183Pro founder mutation is more prevalent.
Management requires a strict lifelong, protein-restricted diet that severely limits the intake of branched-chain amino acids, specifically leucine, isoleucine, and valine. Infants and children rely on specialized, leucine-free metabolic formulas paired with carefully measured amounts of natural protein to support growth without overwhelming the missing enzyme. Patients require regular quantitative blood amino acid monitoring to keep plasma leucine levels within a safe, non-toxic range.
liver transplant is considered a functional cure. Although the BCKDHB defect persists in other body tissues like muscle, the donor liver supplies approximately 10 to 13 percent of total body branched-chain keto acid dehydrogenase activity. This is sufficient to normalize amino acid metabolism, eliminate the risk of acute metabolic decompensation, and allow patients to transition to an unrestricted, normal protein diet, although it cannot reverse preexisting neurological damage.
Metabolic crises are triggered by physiological stress that causes muscle breakdown (catabolism), including common viral infections, high fever, prolonged fasting, trauma, or surgery. Warning signs include an intensification of the sweet, maple syrup odor in cerumen or urine, followed by poor feeding, sudden lethargy, vomiting, irritability, muscle rigidity, and unsteady gait. Because high leucine levels rapidly cause cerebral edema, any sign of illness demands immediate hospital intervention with high-calorie intravenous fluids to halt catabolism.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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