The SLC22A5 gene helps move carnitine, a substance your body uses to turn fat into energy, into cells and back into the kidneys so it is not lost in urine. If this transport system does not work well, carnitine levels can drop and the body may struggle to fuel the heart, muscles, and liver. Pathogenic variants in the SLC22A5 gene can cause primary carnitine deficiency, which may lead to low blood sugar, muscle weakness, tiredness, or heart problems. Some people first learn about this gene through newborn screening or a relative’s diagnosis.
What is a gene?
Genes are stretches of DNA that hold instructions your cells use to make molecules or manage processes in the body. Some genes provide the directions for producing proteins, the active parts of cells. Others mainly regulate when certain processes happen, where they happen, and how strongly they occur. Taken together, genes affect how the body develops and works, and they can influence how you respond to food, stress, or medications. For a more detailed look at this topic, you can find additional information in LearnHub.
Overview
SLC22A5Gene function
What if the gene works
The SLC22A5 gene helps move carnitine into cells and keep enough of it in the body. This supports fat use for energy, especially in the heart, muscles, and during fasting.
Risk
What if the gene does not work
Variants in the SLC22A5 gene can cause primary carnitine deficiency by reducing carnitine transport. People may develop low blood sugar, muscle weakness, tiredness, or heart problems. Milder and severe variants can change when symptoms start and how marked they are.
Treatment
What does that mean for your treatment
Pathogenic variants in the SLC22A5 gene make carnitine replacement the key treatment, usually as lifelong oral levocarnitine. Intravenous carnitine may be used during illness or when oral treatment is not possible.
Conditions associated with SLC22A5
Gene function
What if the gene works
Your muscles, heart, and other tissues need a steady supply of carnitine to use fat for energy. The SLC22A5 gene helps move carnitine from the blood into cells and helps the kidneys keep it in the body. This supports everyday energy needs, especially between meals and during longer activity.
The SLC22A5 gene makes a transporter that brings carnitine into many cells from the bloodstream. This gives cells access to a nutrient they need to move long chain fats into the parts of cells that make energy.
In the kidneys, carnitine enters the forming urine, and the SLC22A5 gene helps take much of it back into the blood. This helps your body conserve carnitine instead of losing large amounts in urine.
By keeping carnitine available, this gene supports normal fat use for energy, especially in muscle and heart. This is a key part of how the SLC22A5 gene helps your body use fat for energy during daily activity and overnight fasting.
What is a variant?
A genetic variant is a small difference in the DNA sequence within a gene. These differences are common and are part of normal human diversity, including differences in appearance, metabolism, or the way the body responds to environmental influences. Many variants do not have any noticeable effect and simply represent natural genetic variation. In some situations, though, a variant can change how a gene functions to a greater extent and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Understanding how SLC22A5 gene variants affect carnitine transport starts with the fact that these DNA changes can alter the transporter’s shape, stability, or placement on the cell surface. Some variants leave partial activity, while more disruptive variants can sharply reduce or stop carnitine uptake into cells. When both copies of the SLC22A5 gene are affected, lower remaining transport is often linked to earlier or more noticeable primary carnitine deficiency, while milder variants may have a less marked effect.
How variants are linked to conditions
Pathogenic variants in both copies of the SLC22A5 gene cause primary carnitine deficiency, also called carnitine uptake defect. This well-established SLC22A5 gene condition can be linked to low carnitine levels and may affect the heart, liver, muscles, and blood sugar, although some people are identified only through newborn screening. Carrying one variant is usually not enough to cause the condition.
A variant is not necessarily a diagnosis
Genetic variants are a usual part of human biology and are widespread in the general population. Most do not directly affect health and instead represent natural human diversity. For many genes, carrying a variant associated with a condition indicates a possible link rather than a definite diagnosis, particularly when multiple genes and environmental factors play a role. 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 people with disease-causing changes in both copies of SLC22A5, risk is mostly set by the gene itself. Long periods without food, infections, and other physical stress can bring on symptoms or make them worse, and pregnancy can add extra strain. Early diagnosis and steady treatment help lower the risk of serious complications.
Inheritance of SLC22A5 variants
SLC22A5-related primary carnitine deficiency is inherited in an autosomal recessive pattern. This means a child usually inherits one SLC22A5 gene variant from each parent, and the parents are often healthy carriers. When both parents carry a variant, each pregnancy has a 25% chance of being affected, a 50% chance of producing a carrier child, and a 25% chance of producing a child without either familial variant. In practical terms, how SLC22A5 variants are inherited depends on both copies of the gene being changed for the condition to develop.
What does my SLC22A5 result mean for my family?
For families, an SLC22A5 result usually matters most for brothers, sisters, and future children. This gene is linked to primary carnitine deficiency in a recessive pattern, so close relatives may also be carriers, and some may have the condition if they inherited changed copies from both parents. A parent, brother, sister, or adult child may choose to learn whether they carry the family’s gene change, especially when planning a pregnancy.
Genetic information
Genetic testing
How you find out about variants
Variants in the SLC22A5 gene are found with SLC22A5 genetic testing, usually on a blood or saliva sample. A lab reads the DNA code to look for changes in this gene and may compare the result with known disease causing and benign variants to clarify whether a finding supports a diagnosis or carrier status.
When should I consider getting a genetic test?
Consider testing for the SLC22A5 gene if newborn screening shows low carnitine, or if someone has unexplained low blood sugar, muscle weakness, or heart problems that suggest primary carnitine deficiency, an inherited condition that affects energy use. Testing can also help when a close family member has this condition or a known SLC22A5 variant.
A genetic result is only one part of your health story
A genetic result can provide useful insight, but what it can tell you varies based on the condition and the kind of variant involved. How the body functions over time is shaped by many factors, including lifestyle, environment, age, and medical history. With some conditions, especially those influenced by many genes, genetic information offers context rather than certainty and is most helpful when viewed alongside other parts of care. In other situations, a genetic result may give a clear answer. In areas like medication response, genetic results can also help put individual experiences into context.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how people respond to medicines. Small differences in genes can change how the body absorbs, moves, breaks down, or clears a drug. This helps explain why the same treatment works well for one person, seems weaker in another, or causes more side effects in someone else. These differences are common and are just one part of the bigger picture, along with age, overall health, and other medicines.
What is Pharmacogenetics?
Pharmacogenetics examines how genetic differences can affect a person’s response to medications. By looking at relationships 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 how strongly a drug works or how the body processes it. This information can support treatment decisions that are both more informed and more individualized. If you want to learn more about this topic, more information is available in the LearnHub.
Drugs influenced by the SLC22A5 gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in guiding medication choices, so questions about side effects, new symptoms, or how a treatment may affect you are best discussed with your doctor. SLC22A5 has been studied in research on carnitine handling and possible interactions with some medicines, but this has not become standard prescribing guidance.
History
Primary carnitine deficiency was recognized clinically before the SLC22A5 gene was identified, as doctors described children and adults with low carnitine levels and problems affecting energy use. In the late 1990s, researchers linked these cases to variants in the SLC22A5 gene, which marked an important step in clarifying the inherited cause. From these first observations, research expanded steadily. Scientists then connected the gene to the OCTN2 transporter, helping unify earlier reports that had seemed separate. As newborn screening became more common in many countries, more people with SLC22A5-related findings were identified early, including some who had few or no symptoms at the time of testing. This shift helped move the condition from a rare clinical puzzle to a better recognized inherited condition.