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BCKDHA
branched chain keto acid dehydrogenase E1 subunit alpha
The *BCKDHA* gene provides instructions for a key component of an enzyme complex critical for breaking down specific amino acids, with variants linked to Maple Syrup Urine Disease. The *BCKDHA* gene encodes an alpha subunit of the branched-chain alpha-keto acid dehydrogenase (BCKD) enzyme complex.
BCKDHA is located on the long (q) arm of chromosome 19, at band 19q13.2. Arm ratio per GRCh38 - banding schematic.
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Overview
The *BCKDHA* gene (branched chain keto acid dehydrogenase E1 subunit alpha) plays a fundamental role in human metabolism [HGNC:986]. It provides the genetic blueprint for one of the subunits of the branched-chain alpha-keto acid dehydrogenase (BCKD) enzyme complex. This enzyme system is essential for the breakdown of branched-chain amino acids (BCAAs), which are crucial for energy production within cells. Disruptions to *BCKDHA* function can lead to metabolic disorders.
What the gene does
The gene product from *BCKDHA* assembles with a corresponding protein from *BCKDHB* to create the E1 component of a multi-part enzyme complex [UniProt:P12694]. Specifically, two copies of the alpha subunit pair with two beta subunits to form this functional unit. Operating within mitochondria, the BCKD complex catalyses a key step in processing leucine, isoleucine, and valine. These three essential amino acids arrive through dietary sources, including protein-rich foods such as meat, dairy products, and eggs. Through the actions of this enzyme complex, these amino acids are transformed into intermediates that cells can harness for energy generation.
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Chromosome location
The *BCKDHA* gene is located on chromosome 19 at band 19q13.2 [HGNC:986]. This specific genomic address helps to pinpoint the gene's position within the human genome. The gene directs the synthesis of a protein comprising 445 amino acids, which forms part of a larger enzyme complex involved in metabolic processes.
Protein structure
The BCKDHA protein consists of 445 amino acids [UniProt:P12694]. Its structural composition includes a disordered region, spanning amino acids 33-52. This region may contribute to the protein's flexibility or its interaction with other molecules within the branched-chain alpha-keto acid dehydrogenase enzyme complex.
Key variants
Genetic variations, or variants, in the *BCKDHA* gene can affect the protein's ability to function correctly. More than 80 different pathogenic variants in *BCKDHA* have been identified in individuals with Maple Syrup Urine Disease. These variants can lead to a range of impacts, from subtle changes in enzyme activity to complete loss of function, influencing the severity and presentation of associated conditions.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1121G>A | p.Trp374Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Maple syrup urine disease |
c.1237dup | p.Tyr413fs | Pathogenic/Likely pathogenic | ★★☆☆ | Maple syrup urine disease |
c.164del | p.Pro55fs | Pathogenic/Likely pathogenic | ★★☆☆ | Maple syrup urine disease type 1A |
c.308T>C | p.Leu103Pro | Pathogenic/Likely pathogenic | ★★☆☆ | Maple syrup urine disease type 1A |
c.402del | p.Tyr135fs | Pathogenic/Likely pathogenic | ★★☆☆ | Maple syrup urine disease |
c.410_426dup | p.Gly143fs | Pathogenic/Likely pathogenic | ★★☆☆ | Maple syrup urine disease |
c.507C>G | p.Tyr169Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Maple syrup urine disease |
c.529C>T | p.Gln177Ter | Pathogenic | ★★☆☆ | Maple syrup urine disease type 1A |
c.67del | p.Leu23fs | Pathogenic/Likely pathogenic | ★★☆☆ | Maple syrup urine disease type 1A |
c.691del | p.Val231fs | Pathogenic/Likely pathogenic | ★★☆☆ | Maple syrup urine disease type 1A |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Pathogenic variants in the *BCKDHA* gene are primarily associated with Maple Syrup Urine Disease, an autosomal recessive metabolic disorder. This condition is characterised by the body's inability to properly break down branched-chain amino acids (leucine, isoleucine, and valine). Many *BCKDHA* variants are linked to the severe, classic form of Maple Syrup Urine Disease, which typically presents shortly after birth.
Inheritance pattern
Conditions caused by pathogenic BCKDHA variants typically follow autosomal recessive inheritance.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
UK clinical status
The *BCKDHA* gene is recognised within several UK NHS National Genomic Test Directory panels, indicating its clinical significance for genetic testing in the UK. It is categorised as 'green' for conditions such as DDG2P, Early onset or syndromic epilepsy (R59), Hyperammonaemia, Intellectual disability (R29), Likely inborn error of metabolism (R98), and Undiagnosed metabolic disorders.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
Individuals with conditions such as Maple Syrup Urine Disease, which are associated with *BCKDHA* variants, typically require strict dietary management to limit the intake of branched-chain amino acids. This often involves specialised formulas and low-protein foods. Any dietary or lifestyle modifications should always be discussed with a healthcare professional or a registered dietitian.
Supplement considerations
While specific dietary management is crucial for conditions related to *BCKDHA* variants, there is no conclusive evidence that dietary supplements can prevent or treat Maple Syrup Urine Disease. Individuals considering any supplements should consult with their healthcare provider to ensure safety and appropriateness.
Frequently asked questions
What is the primary function of the *BCKDHA* gene?
The *BCKDHA* gene provides instructions for making a critical alpha subunit of the branched-chain alpha-keto acid dehydrogenase (BCKD) enzyme complex. This complex is vital for breaking down specific amino acids (leucine, isoleucine, and valine) in the body.
What condition is most commonly associated with *BCKDHA* variants?
Variants in the *BCKDHA* gene are primarily associated with Maple Syrup Urine Disease, a metabolic disorder that affects the body's ability to process branched-chain amino acids.
How is Maple Syrup Urine Disease inherited?
Maple Syrup Urine Disease is inherited in an autosomal recessive pattern. This means an individual must inherit two altered copies of the *BCKDHA* gene (one from each parent) to develop the condition.
References
- Quental S, Macedo-Ribeiro S, Matos R. Molecular and structural analyses of maple syrup urine disease and identification of a founder mutation in a Portuguese Gypsy community. Molecular genetics and metabolism. 2008. PMID: 18378174
- Flaschker N, Feyen O, Fend S. Description of the mutations in 15 subjects with variant forms of maple syrup urine disease. Journal of inherited metabolic disease. 2007. PMID: 17922217
- Rodríguez-Pombo P, Navarrete R, Merinero B. Mutational spectrum of maple syrup urine disease in Spain. Human mutation. 2006. PMID: 16786533
- Puffenberger EG. Genetic heritage of the Old Order Mennonites of southeastern Pennsylvania. American journal of medical genetics. Part C, Seminars in medical genetics. 2003. PMID: 12888983
- Henneke M, Flaschker N, Helbling C. Identification of twelve novel mutations in patients with classic and variant forms of maple syrup urine disease. Human mutation. 2003. PMID: 14517957
- Adam MP, Bick S, Mirzaa GM. Maple Syrup Urine Disease. 1993. PMID: 20301495