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

HLCS gene

The HLCS gene provides instructions for an enzyme essential for the body's effective use of biotin, a critical B vitamin.

Normal Function

The HLCS gene produces the enzyme holocarboxylase synthetase. This enzyme is responsible for activating biotin-dependent carboxylases by attaching biotin to them. These carboxylases are vital for cellular functions, including the metabolism of proteins, fats, and carbohydrates.

Additionally, holocarboxylase synthetase helps regulate the transcription (activity) of genes involved in the transport and use of biotin. This process is necessary for the proper function of tissues such as the brain, muscles, liver, and kidneys.

Health Conditions Related to Genetic Changes

Holocarboxylase synthetase deficiency

Mutations in the HLCS gene lead to holocarboxylase synthetase deficiency, a condition where the body cannot use biotin effectively. Symptoms typically appear in infancy and include:

  • Difficulty feeding
  • Breathing problems
  • Skin rash
  • Hair loss (alopecia)
  • Lethargy

If left untreated, the deficiency can result in severe complications, including delayed development, seizures, and coma. Most known mutations occur in the region of the enzyme that binds to biotin, reducing its ability to activate carboxylases. Without active carboxylases, the body cannot process nutrients effectively, and the regulation of biotin-related genes may be impaired.

Frequently Asked Questions

Holocarboxylase synthetase deficiency is often detected through newborn screening programs, which test for elevated levels of certain organic acids in the blood or urine. If the screening is positive, further diagnostic tests, such as enzyme activity assays or genetic testing for HLCS gene mutations, are performed to confirm the diagnosis.
The primary treatment is lifelong supplementation with biotin, a B vitamin. When started early and maintained consistently, biotin supplementation is highly effective in preventing or reversing most of the severe symptoms and complications, allowing affected individuals to live healthy lives.
Holocarboxylase synthetase deficiency is an autosomal recessive condition. This means both parents must carry a copy of the altered HLCS gene for their child to inherit the disorder. If one child is affected, there is a 25% chance that each subsequent child born to the same parents will also have the condition.
Parents should watch for a return of symptoms such as difficulty feeding, breathing problems, skin rash, hair loss, or increased lethargy. These signs could indicate that the biotin dosage needs adjustment, the child is not taking the medication consistently, or they are experiencing an illness that exacerbates their metabolic state, requiring prompt medical evaluation.
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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