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BCS1L gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

BCS1L gene

The BCS1L gene provides instructions for a protein essential for mitochondrial energy production and the assembly of complex III.

Normal Function

The BCS1L protein is critical for the formation of complex III within mitochondria. It specifically adds the Rieske Fe/S protein to the complex. Complex III is a vital part of oxidative phosphorylation, the process by which cells generate adenosine triphosphate (ATP), their primary energy source.

As a byproduct of oxidative phosphorylation, complex III produces reactive oxygen species. While these can damage DNA and tissues, they also serve as important signals for cells, particularly during low-oxygen conditions (hypoxia).

Health Conditions Related to Genetic Changes

Björnstad syndrome

Mutations in BCS1L can cause this syndrome, which is characterized by pili torti (twisted hair) and hearing loss. These mutations impair the ability of BCS1L to assemble complex III, leading to reduced oxidative phosphorylation and an abnormal buildup of Rieske Fe/S protein. The condition is associated with excessive production of reactive oxygen species by complex I, which is believed to damage hair follicles and inner ear tissues.

GRACILE syndrome

Found almost exclusively in Finland, this severe, lethal condition is caused by a specific mutation (Ser78Gly) that leads to a deficiency of the BCS1L protein. This results in decreased complex III activity and oxidative phosphorylation, particularly in the liver and kidneys. Infants with this syndrome exhibit low birth weight, liver and kidney dysfunction, and iron overload.

Mitochondrial complex III deficiency

BCS1L mutations can cause this deficiency, which typically affects the liver (hepatopathy), kidneys (tubulopathy), and brain (encephalopathy). The loss of complex III function reduces cellular energy and increases the production of reactive oxygen species, leading to damage in these vital organs.

Leigh syndrome

The BCS1L gene is also associated with Leigh syndrome, a severe neurological disorder.

Other Names for This Gene

  • BC1 (ubiquinol-cytochrome c reductase) synthesis-like
  • BCS1
  • BCS1-like protein
  • BCS1_HUMAN
  • h-BCS1
  • Hs.6719
  • mitochondrial chaperone BCS1
  • mitochondrial complex III assembly

Frequently Asked Questions

BCS1L-related conditions follow an autosomal recessive inheritance pattern. A child must inherit a mutated copy of the BCS1L gene from both parents to be affected. When both parents are unaffected carriers, each pregnancy carries a 25 percent chance of producing an affected child, a 50 percent chance of producing an unaffected carrier, and a 25 percent chance of producing a child with two normal copies of the gene. Carrier testing and prenatal genetic diagnosis are available for families with known mutations.
The severity and nature of the disorder depend on how significantly the specific mutation disrupts the BCS1L protein's function. Mild or hypomorphic mutations impair the incorporation of the Rieske iron-sulfur protein just enough to cause oxidative stress in rapidly growing, sensitive tissues, manifesting as hair and inner ear defects in Bjornstad syndrome. Conversely, severe missense variants, such as the Finnish founder mutation Ser78Gly, severely decrease complex III assembly across vital organs, causing profound mitochondrial failure in the liver and kidneys characteristic of lethal GRACILE syndrome.
Infants require close multidisciplinary surveillance focusing on organ systems vulnerable to mitochondrial failure. Essential monitoring includes serial liver function tests, coagulation profiles, renal tubular function assessments to detect Fanconi-like tubulopathy, blood lactate and blood gas measurements, and iron studies to track hepatic iron accumulation. Formal audiology evaluations should be initiated early to identify sensorineural hearing loss, and supportive care must prioritize avoiding dehydration, fasting, and medications that worsen mitochondrial toxicity.
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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