The ACAT1 gene gives your cells instructions to help break down certain fats and the amino acid isoleucine, especially when your body is using ketones for energy. If it does not work properly, acids and ketones can build up and trigger episodes of vomiting, dehydration, fast breathing, and unusual sleepiness, often during illness or fasting. This gene plays an important role in keeping energy use steady, particularly in infants and children. Pathogenic variants in the ACAT1 gene cause beta-ketothiolase deficiency, a rare inherited condition identified with genetic and metabolic testing.
What is a gene?
Genes are stretches of DNA that give your cells instructions for making molecules or managing activities in the body. Some genes carry the code for proteins, which do much of the work inside cells. Others mainly regulate when certain processes happen, where they occur, and how active they are. Together, genes affect how the body develops and works, and they can also shape how you respond to food, stress, and medications. For a more detailed look at this topic, you can find more in the LearnHub.
Overview
ACAT1Gene function
What if the gene works
The ACAT1 gene helps cells turn certain fats and protein building blocks into energy. It is especially important for using ketones, which are fuels the body makes during fasting or illness.
Risk
What if the gene does not work
More disruptive variants in the ACAT1 gene can cause beta-ketothiolase deficiency, which affects ketone and isoleucine breakdown. Milder and more severe variants can change when acid buildup episodes start, often in infancy or childhood, and how intense they are.
Treatment
What does that mean for your treatment
Pathogenic variants in the ACAT1 gene are managed with a metabolic emergency plan: avoid prolonged fasting, and during illness use early glucose support, sometimes glucose through a vein, to lower the chance of crises. Some people also use carnitine and a tailored protein or isoleucine intake plan, based on metabolic follow up. No approved drug that directly targets the ACAT1 gene is standard care.
Conditions associated with ACAT1
Gene function
What if the gene works
Your cells use the ACAT1 gene to help turn certain fats and protein building blocks into energy. Its protein works mainly inside mitochondria, the parts of cells that act as energy centers. Understanding what the ACAT1 gene does in the body helps explain how your body handles ketones, an energy source made when glucose is lower.
Inside mitochondria, the ACAT1 gene helps split a small fuel molecule called acetoacetyl-CoA into two acetyl-CoA molecules. Your cells can then feed these into their main energy-making pathway. This supports steady energy use in everyday life.
This gene helps your body use ketones, which are made from fat when glucose is less available. That can matter overnight, between meals, or during longer exercise. It supports a flexible fuel supply for many tissues.
The ACAT1 gene also helps process isoleucine, one of the amino acids from dietary protein. This lets your cells recover useful energy parts from food. It is one step in normal nutrient handling.
What is a variant?
A genetic variant is a slight difference in the DNA sequence within a gene. These changes 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. Sometimes, though, a variant changes how a gene works more significantly and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the ACAT1 gene can change the enzyme’s shape, stability, or ability to pair with itself, which lowers or abolishes its activity inside mitochondria, the cell’s energy centers. In descriptions of how ACAT1 gene variants affect enzyme activity, milder changes usually leave some function, while more disruptive variants can cause near-complete loss of activity. In beta-ketothiolase deficiency, this difference may influence how early episodes begin and how pronounced they are.
How variants are linked to conditions
Pathogenic variants in the ACAT1 gene cause beta-ketothiolase deficiency, also called mitochondrial acetoacetyl-CoA thiolase deficiency. This rare inherited condition is linked to episodes of vomiting, dehydration, deep rapid breathing, and reduced alertness, often during illness or fasting, with symptom-free periods in between. Finding disease-causing variants in both copies of the ACAT1 gene can confirm the diagnosis.
A variant is not necessarily a diagnosis
Variants in genes are a routine part of human biology and are widespread in the general population. Most do not directly affect health and instead reflect natural differences among people. 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 play a role. In some situations, though, a single well-characterized variant in a specific gene is enough to confirm the diagnosis.
Are there things that can increase or change my risk?
For ACAT1, the main risk comes from genetics: a child is affected when they inherit changed copies of the gene from both parents, so family history and parents being related by blood can raise the chance. In people living with this condition, illness, long gaps without food, and dehydration can trigger sudden, serious episodes.
Inheritance of ACAT1 variants
Variants in the ACAT1 gene linked to ACAT1-related health conditions are inherited in an autosomal recessive pattern. This means a child inherits one changed copy of the ACAT1 gene from each parent. When both parents carry one variant, each pregnancy has a 25% chance of resulting in a child with the condition, a 50% chance that the child will be a carrier, and a 25% chance that the child will inherit neither variant. In families learning how ACAT1 gene variants are inherited, it helps to know that carriers usually do not have the condition themselves.
What does my ACAT1 result mean for my family?
For families affected by an ACAT1 result linked to beta-ketothiolase deficiency, close relatives may also carry the same gene change, even if they feel completely well. Brothers and sisters may be affected or may be carriers, and parents are usually carriers. Other relatives, such as aunts, uncles, and cousins, may also carry the change, so the result can be relevant beyond just one person.
Genetic information
Genetic testing
How you find out about variants
ACAT1 genetic testing looks for changes in the ACAT1 gene using a blood sample, saliva sample, or cheek swab. This type of testing reads the gene’s DNA to identify variants linked to beta-ketothiolase deficiency and can clarify whether a person has the condition or carries a familial variant.
When should I consider getting a genetic test?
Consider ACAT1 genetic testing if a baby or child has repeated episodes of severe vomiting, dehydration, unusual sleepiness, or fast breathing during illness, especially when doctors find very high ketones or acid buildup in the blood. Testing can also help when this condition runs in the family or a relative has a known ACAT1 variant.
A genetic result is only one part of your health story
Genetic results can be very informative, but what they can tell you varies based on the condition and the specific type of variant. Over time, the way the body works is also shaped by factors such as lifestyle, environment, age, and medical history. For some conditions, especially those influenced by many genes, genetic information provides context rather than certainty and is best considered alongside other parts of care. In other situations, a genetic result may give a clear answer. In areas like medication response, genetic information 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. A treatment that works well for one person may work less well for another, or may cause more side effects, because the body can absorb, break down, transport, or respond to a drug in different ways. These inherited differences are common and are one reason medication response can vary from person to person.
What is Pharmacogenetics?
Pharmacogenetics examines how genetic differences shape a person’s response to medications. It focuses on connections between genes and drugs to help explain why the same treatment may work differently from one person to another. For many medicines, genes can affect both how strongly a drug works and how the body handles it. This understanding can support treatment decisions that are more informed and more individualized. To explore this topic further, more information is available in the LearnHub.
Drugs influenced by the ACAT1 gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in predicting how people respond to medicines, so routine treatment decisions are not usually based on it. If you have concerns about side effects, supplements, or how your health condition may affect treatment, speak with your doctor or pharmacist.
History
ACAT1 entered medical genetics through studies of children with repeated episodes of ketoacidosis, a pattern now known as beta ketothiolase deficiency. Initially understood only through visible traits, later recognized as tied to a specific gene, this condition was described in the 1970s as doctors linked unusual metabolic crises to a missing enzyme activity. From these first observations, research expanded steadily. In the 1990s, scientists identified the ACAT1 gene and confirmed that different variants could cause the condition in affected families. That discovery improved diagnosis and helped distinguish ACAT1 related illness from other inherited metabolic conditions with similar symptoms. Over time, descriptions became more precise as newborn screening and molecular testing made earlier recognition possible.