Your body uses the HLCS gene to activate several enzymes that need biotin (vitamin B7), helping you turn protein, fats, and carbohydrates into energy. This gene plays an important role in keeping these chemical steps running smoothly. When both copies of the gene do not work well, a person can develop holocarboxylase synthetase deficiency, which may cause poor feeding, low energy, skin rash, breathing problems, or seizures, often starting in infancy. Early treatment with biotin can greatly improve symptoms and reduce metabolic crises.
What is a gene?
Genes are sections of DNA that carry instructions your cells use to make molecules or regulate processes in the body. Some genes hold the instructions for making proteins, which are the parts of cells that do much of the work. Other genes mainly help direct when certain processes happen, where they take place, and how strongly they occur. Taken together, genes affect how the body develops and functions, and they can influence how you respond to food, stress, or medications. To explore this topic more deeply, you can learn more in the LearnHub.
Overview
HLCSGene function
What if the gene works
The HLCS gene helps your body attach biotin, a B vitamin, to several enzymes. This supports breaking down protein, fat, and carbohydrates and helps the body make energy.
Risk
What if the gene does not work
Variants in the HLCS gene can cause holocarboxylase synthetase deficiency, a treatable condition that disrupts energy use. Babies may have poor feeding, rash, breathing problems, or seizures, while milder variants can lead to later and less severe symptoms.
Treatment
What does that mean for your treatment
Pathogenic or loss-of-function variants in the HLCS gene usually mean treatment includes lifelong high-dose biotin, which can markedly improve metabolic stability when started promptly. Biotin is a vitamin-based treatment rather than a typical drug, and it is usually continued long term because symptoms can return if it is stopped.
Conditions associated with HLCS
Gene function
What if the gene works
Your cells use the HLCS gene to switch on a small group of enzymes that depend on biotin, also called vitamin B7. Once active, these enzymes support routine jobs in energy use, glucose supply, and fat metabolism. Understanding how the HLCS gene works helps explain how your body keeps fuel supplies steady from meal to meal.
HLCS adds biotin (vitamin B7) to several enzymes that need it to work. This step switches those enzymes into their active forms.
By activating these enzymes, HLCS supports making glucose when your body needs fuel between meals. It also helps cells draw energy from parts of certain amino acids.
HLCS also supports enzymes that help build fatty acids and manage fat use in tissues. These pathways help cells make membranes and store energy in a controlled way.
What is a variant?
A genetic variant is a minor change in a gene’s DNA sequence. These changes are common and are part of normal human diversity, including differences in appearance, metabolism, and the way the body responds to environmental influences. Many do not have any noticeable effect and simply represent natural genetic variation. Sometimes, though, a variant changes how a gene works more substantially and can contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
HLCS gene variants can change the enzyme’s shape, stability, or ability to bind biotin, so cells activate several biotin dependent enzymes less effectively. Descriptions of how HLCS gene variants affect enzyme activity usually reflect a spectrum, not an all or none change. Some missense variants leave partial activity, while more disruptive splice, frameshift, or stop variants can greatly reduce or abolish activity. This can influence how early holocarboxylase synthetase deficiency appears and how broad its features are.
How variants are linked to conditions
Pathogenic variants in the HLCS gene cause holocarboxylase synthetase deficiency, also called HLCS-related multiple carboxylase deficiency. This inherited condition often begins in infancy, though some people are diagnosed later in childhood. In families with a known HLCS gene variant, finding the same pathogenic variant can confirm the diagnosis.
A variant is not necessarily a diagnosis
Genetic variants are a routine part of human biology and are common throughout the general population. Most do not have a direct effect on health and instead reflect natural human diversity. For many genes, carrying a variant associated with a condition suggests a possible link rather than a definite diagnosis, especially when multiple genes and environmental factors also contribute. In some situations, though, a single well-characterized variant in a specific gene is enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For HLCS, risk is mostly set by inheritance: a child is affected when they inherit a changed HLCS copy from both parents, so having two carrier parents raises the chance. In people living with this condition, illness, long gaps without food, or missing biotin treatment can trigger or worsen symptoms.
Inheritance of HLCS variants
HLCS gene inheritance follows an autosomal recessive pattern for HLCS-related holocarboxylase synthetase deficiency. This means a child usually inherits one HLCS variant from each parent. Parents who each carry one variant are often unaffected themselves, but with each pregnancy there is a 25% chance the child will have the condition, a 50% chance the child will be a carrier, and a 25% chance the child will inherit neither variant. Sons and daughters are affected at the same rate.
What does my HLCS result mean for my family?
For HLCS, family members can sometimes carry the same gene change without having symptoms. Parents of a child with an HLCS-related condition are often healthy carriers, and brothers or sisters may also be affected or be carriers. Other close relatives, such as aunts, uncles, and cousins, may also carry the change, so the result can matter beyond one person.
Genetic information
Genetic testing
How you find out about variants
A blood or saliva sample can be used to look for variants in the HLCS gene. This kind of genetic testing for HLCS variants reads the gene’s DNA code to find changes that may help confirm a rare condition that affects how the body uses biotin.
When should I consider getting a genetic test?
Consider HLCS genetic testing if a baby or child has a positive newborn screen or signs of this rare condition, such as poor feeding, vomiting, unusual sleepiness, breathing problems, seizures, a skin rash, or hair loss. It may also help when there is a family history, because a confirmed result can guide quick treatment with biotin.
A genetic result is only one part of your health story
Genetic results can provide useful insight, but what they can tell you varies based on the condition and the kind of variant involved. Over time, how the body works is shaped by many factors, including lifestyle, environment, age, and medical history. For some conditions, especially those influenced by many genes, genetic information offers context rather than certainty and is best considered alongside other parts of care. In other situations, a genetic result can give a clear answer. In areas such as medication response, these results can also help place individual experiences in context.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how people respond to medicines. Some people break down a drug more slowly or more quickly, while others may be more or less sensitive to its effects. This helps explain why the same treatment can work well for one person, have little effect for another, or cause more side effects in someone else.
What is Pharmacogenetics?
Pharmacogenetics examines how genetic differences can affect a person’s response to medication. By looking at links between genes and drugs, it helps explain why the same treatment may work differently from one person to another. For many medicines, genes can influence both how strongly a drug works and how the body processes it. This information can support treatment decisions that are more informed and more individualized. More detailed information on this topic is available in the LearnHub.
Drugs influenced by the HLCS gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in how people respond to medicines. If you have questions about symptoms, treatment, or supplements such as biotin, it is best to talk with your doctor.