The ACAD9 gene helps mitochondria, the parts of cells that make energy, build complex I, a key part of the cell’s energy system. If the ACAD9 gene is not working well, cells may struggle to make enough energy, especially in the heart, muscles, brain, and liver. People with harmful variants in the ACAD9 gene can have an inherited mitochondrial condition that may cause low muscle tone, feeding problems, tiredness, developmental delay, or heart problems. Symptoms and severity vary widely from person to person.
What is a gene?
A gene is a stretch of DNA that holds instructions your cells use to make molecules or regulate processes in the body. Some genes carry the information needed to produce proteins, the parts of cells that do the work. Others mainly help control when certain processes occur, where they take place, and how strongly they run. Together, genes affect how the body develops and functions, and they can also influence how you respond to food, stress, and medications. For a closer look at this topic, you can find more in the LearnHub.
Overview
ACAD9Gene function
What if the gene works
The ACAD9 gene helps mitochondria, your cells’ energy centers, build an important system for making energy. It also helps break down certain fats for fuel.
Risk
What if the gene does not work
When the ACAD9 gene does not work properly, cells make less energy, which can lead to muscle weakness, heart problems, and delayed development. Milder to more severe variants can affect when symptoms begin and how strongly they appear.
Treatment
What does that mean for your treatment
For pathogenic variants in the ACAD9 gene, no treatment or medication selection approach is currently established in clinical guidelines. Riboflavin is often tried in ACAD9 deficiency because some people improve, especially in heart or muscle symptoms, but response varies.
Conditions associated with ACAD9
Gene function
What if the gene works
Your mitochondria need the ACAD9 gene to keep cellular energy production running smoothly. Its main job is helping build complex I, a major part of the energy-making chain in mitochondria. Understanding ACAD9 gene function helps explain how cells make steady energy for everyday work.
The ACAD9 gene helps your cells put together complex I, a large protein group inside mitochondria. It supports the step by step joining of parts so this energy-making unit forms properly.
By supporting complex I, the ACAD9 gene helps mitochondria start the chain of reactions that makes ATP (the cell’s main energy source). This gives cells a steady supply of usable energy for routine body functions.
What is a variant?
A genetic variant is a small difference in the DNA sequence of a gene. These differences are common and help shape normal human diversity, including variation in appearance, metabolism, and how the body responds to environmental influences. Many variants do not cause any noticeable effect and simply represent natural genetic variation. In some situations, though, a variant can change how a gene functions more substantially and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the ACAD9 gene can make the ACAD9 protein unstable, shorten it, or change its shape so it may not work well or join with mitochondrial complex I, a key part of the cell's energy system. Some ACAD9 gene variants leave partial activity, while more severe variants can greatly reduce or nearly eliminate protein function. This range in effect can influence how much cellular energy drops and, in ACAD9 deficiency, may affect how early and how strongly features appear.
How variants are linked to conditions
Pathogenic variants in the ACAD9 gene cause ACAD9 deficiency, a mitochondrial condition with a range of ACAD9 deficiency symptoms. People may have heart muscle disease, low muscle tone, feeding problems, developmental delay, exercise intolerance, or episodes of lactic acidosis (a buildup of acid in the blood). Symptoms can differ greatly, from severe illness in infancy to milder adult forms. Finding disease causing variants in both copies of the ACAD9 gene can confirm the diagnosis.
A variant is not necessarily a diagnosis
Genetic variants are a routine part of human biology and are widely present in the general population. Most do not have a direct impact on health and instead are part of normal human diversity. For many genes, carrying a variant associated with a condition suggests a possible link rather than a certain diagnosis, especially when several genes and environmental factors are involved. In some situations, however, 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 ACAD9, the main risk comes from inheriting disease-causing changes in both copies of the gene, so lifestyle does not meaningfully change whether the condition occurs. Symptoms can be brought on or worsened by illness, fasting, or heavy physical stress in some people, which can raise the chance of complications.
Inheritance of ACAD9 variants
Variants in the ACAD9 gene are inherited in an autosomal recessive pattern, which means a person usually needs to inherit two disease-causing ACAD9 variants, one from each parent, to have ACAD9-related disease. Parents who each carry one variant are typically unaffected carriers, and with each pregnancy they have a 25% chance of having an affected child, a 50% chance of having a child who is a carrier, and a 25% chance of having a child with neither variant. This ACAD9 inheritance pattern affects sons and daughters equally because the ACAD9 gene is on chromosome 3, which is not a sex chromosome.
What does my ACAD9 result mean for my family?
For families with an ACAD9-related condition, the pattern is usually recessive, which means parents are often healthy carriers. Brothers and sisters may also be affected or may be carriers, and other close relatives could carry the same gene change without knowing it. This can matter for future pregnancies and for relatives who want to understand their own chance of being a carrier.
Genetic information
Genetic testing
How you find out about variants
Genetic testing for ACAD9 variants uses a blood sample, saliva, or sometimes a cheek swab. A lab reads the DNA in the ACAD9 gene to look for changes that may explain symptoms or help confirm an inherited condition. Results may identify a pathogenic variant, a benign variant, or a variant of uncertain significance, meaning its effect is not yet clear.
When should I consider getting a genetic test?
Genetic testing for the ACAD9 gene may be worth considering if a child or adult has signs of an inherited condition that affects how the body makes energy, such as weak muscles, tiring easily, heart muscle disease, developmental delay, or repeated high lactic acid levels. It can also help clarify a family history of this condition.
A genetic result is only one part of your health story
Genetic results can provide insight, but what they show varies with the condition and the type of variant involved. Lifestyle, environment, age, and medical history shape how the body works over time. For some conditions, especially those influenced by many genes, genetic information adds context rather than certainty and is best understood with other aspects of care. In other cases, a genetic result can give a clear answer. In areas like medication response, it can also help place experiences in context.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how people respond to medicines. Small differences in DNA can change how the body breaks down a drug, moves it through the body, or responds to it at the target tissue. This helps explain why the same treatment may work well for one person, work less well for another, or cause more side effects in someone who is more sensitive to it.
What is Pharmacogenetics?
Pharmacogenetics looks at how differences in a person’s genes affect their response to medications. It examines connections between genes and drugs to help explain why the same treatment may work differently from one person to another. For many medicines, genes influence both how strong a drug’s effects are and how the body handles it. This information can support more informed and more personalized treatment decisions. You can read more about this topic in the LearnHub.
Drugs influenced by the ACAD9 gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in helping doctors choose or adjust medicines, so concerns about side effects, new symptoms, or medicine changes are best discussed with your doctor.
History
The ACAD9 gene entered the medical literature in the early 2000s, when researchers identified it as a member of a known gene family involved in energy metabolism. Over time, scientists’ understanding of the gene’s function has changed. Early work focused on its similarity to other related genes, but later studies showed that ACAD9 also had an important role in mitochondrial disease, especially complex I deficiency. As medical science evolved, so did understanding of this gene, and ACAD9 became recognized as a cause of inherited problems with energy production in some children and adults. These discoveries helped move ACAD9 from a little known research finding into routine discussions in mitochondrial genetics.