Long-Chain Fatty Acid Oxidation Disorders (LC-FAODs): Symptoms, Causes, Treatment

Written by Stephanie Watson
Medically Reviewed by Dan Brennan, MD on May 21, 2025
12 min read

Long-chain fatty acid oxidation disorders (LC-FAODs) are a group of rare inherited conditions that affect metabolism, or how your body converts food into energy. Fatty acids are made from chains of carbon atoms, and long-chain fatty acids have at least 14 carbon atoms. They're in foods like olive oil, fish, avocado, and meat.

People born with LC-FAODs are missing an enzyme that their body needs to break down long-chain fatty acids into energy. As a result, their body doesn't make enough energy to power organs like their heart, muscles, and liver. When fatty acids aren't broken down, they build up in organs and damage them.

LC-FAODs can lead to serious complications like muscle damage, liver failure, severely low blood sugar, high levels of ammonia in the blood, and heart muscle disease. Early diagnosis and dietary changes are essential to managing these conditions.

Symptoms depend on the type of LC-FAOD and the enzyme that's missing. People with mild forms of the disorder may not show symptoms until they're teenagers or adults. Those with more severe forms may start to show symptoms in their first few months or years of life.

What is the first sign of LC-FAODs?

That depends on when symptoms start. Newborns often have heart muscle disease, with symptoms like a hard time breathing, trouble eating, and sleepiness. Infants and children may first show signs of liver problems, such as yellow eyes and skin (jaundice) and low blood sugar.

Other symptoms of (LC-FAODs)   

Children with LC-FAODs may also have symptoms like these:

  • Muscle pain and weakness
  • Trouble exercising
  • Slowed development of speech and movement 

Other symptoms depend on what specific problems the disorder that you have causes.

Symptoms of hypoglycemia (low blood sugar):

  • Pale skin
  • Shaking
  • Sweating
  • Headache
  • Nausea
  • Fast or irregular heartbeat
  • Tiredness
  • Crankiness
  • Dizziness

Symptoms of hyperammonemia (high ammonia levels in the blood):

  • Nausea and vomiting
  • Belly pain
  • Headache
  • Trouble with balance and coordination
  • Behavior changes
  • Reduced muscle tone
  • Slowed development

Symptoms of cardiomyopathy (heart muscle disease):

  • Trouble breathing
  • Chest pain
  • Fast heartbeat
  • Swelling of the legs, ankles, feet, and belly
  • Cough while lying down
  • Tiredness
  • Dizziness

How long do symptoms of LC-FAODs last?

Symptoms usually start during infancy or childhood. They may get worse over time. Some people with LC-FAODs only have symptoms at certain times, such as when they're sick, hungry, or stressed.

FAODs include more than 20 disorders. In each one, a different enzyme is missing. 

There are six main types of LC-FAODs:

Very long chain acyl-CoA dehydrogenase (VLCAD) deficiency

This is the most common LC-FAOD. The most severe form of VLCAD deficiency starts in the first few months of life. Infants and children with this deficiency are at risk of serious heart and liver problems. In the milder form, symptoms often don't show up until the teen or adult years. Adults with VLCAD deficiency may get muscle damage called rhabdomyolysis.

Long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) deficiency

This disorder affects fewer than 1 in 62,000 pregnancies. It usually starts in the first few years of life. Babies and children with LCHAD deficiency have low blood sugar, liver problems, a weak heart, and slowed development. Later in childhood, they may develop muscle pain and damage and lose feeling in their arms and legs from nerve damage.

Trifunctional protein (TFP) deficiency

People with this rare condition, called TFPD, are missing a group of three enzymes in the mitochondria – the energy-producing part of the cell. These enzymes are needed to break down fatty acids. 

Carnitine acylcarnitine translocase (CACT) deficiency

CACT is a protein that helps break down fatty acids and convert them into energy. This type of deficiency is very rare. It usually appears in newborns, and it's very serious. People with the milder form often develop muscle damage as they get older.

Carnitine palmitoyltransferase (CPT) 1 and 2 deficiency

The two CPT enzymes help cells pull in and use fatty acids. CPT deficiencies are very rare. Symptoms usually appear in babies, although some people don't get a diagnosis until later in life. 

Gene changes called mutations cause LC-FAODs. A different gene mutation is responsible for each type. Each of the mutated genes carries instructions for making an enzyme that helps convert long-chain fatty acids into energy. For example, the CPT1A gene that causes CPT1 deficiency codes for an enzyme that helps fatty acids get inside cells. 

LC-FAODs pass down from parents to their children. A child needs to inherit one copy of the mutated gene from each parent to have the disorder. People who only inherit one copy of the gene are carriers. They won't have the disorder, but they can pass it to their children.

No. You can't catch an LC-FAOD from someone else. These disorders pass down from parents to their children through genes.

You're more likely to have one of these disorders if it runs in your family. If both of your parents carry the mutated gene, you have a 25% chance of getting the disorder. Parents who are close relatives are at greater risk of having a child with an LC-FAOD, because they share many of the same genes.

All newborns in the United States are routinely screened for genetic disorders like LC-FAODs. Babies who test positive or show symptoms of these conditions will have more tests to confirm the diagnosis. Screening newborns helps doctors detect these disorders and treat them early. But some people don't get diagnosed until they have symptoms later in life.       

Tests for LC-FAODs 

Tests like these can show whether you or your child has a long-chain fatty acid oxidation disorder:

Newborn screening. When your baby is 1 to 2 days old, a care provider will take a small sample of their blood with a heel stick. A lab tests the blood for different disorders, including LC-FAODs.

Blood and urine tests. These tests check for abnormally high levels of fatty acids and other substances in your blood and urine.

Genetic testing. Testing for the specific gene mutations that cause LC-FAODs can confirm the diagnosis and identify which type of disorder you or your child has.         

What to know when you’re first diagnosed

These conditions are very rare. When you're first diagnosed, it's important to learn about the disorder, how it could affect your health, and what treatment options are available. If you’re planning to have children, you may want to have genetic testing to learn whether your children could also be at risk. If you have a partner, they may want to do the same.

A group of providers will diagnose and care for you or your child. Your treatment team may include a:

Family doctor or pediatrician. This doctor will likely diagnose you, and they'll work with other specialists to manage your care.

Cardiologist. You'll see this doctor for cardiomyopathy or other heart problems.

Hepatologist. This specialist treats liver problems.

Neurologist. This doctor treats nerve and muscle problems.

Metabolic geneticist. This specialist treats children and adults who have inherited metabolic disorders like LC-FAODs.

Dietitian. Nutrition is a big part of managing LC-FAODs. A dietitian will recommend certain foods and supplements to treat your condition.

Diet, supplements, and lifestyle changes are the main treatments for the disorder. Your doctors will also treat any complications that might happen. 

Diet for long-chain fatty acid oxidation disorders (LC-FAODs)

The goal in making dietary changes is to limit the amount of long-chain fats you or your child eats, while still getting enough calories and nutrients to grow and be healthy. Your doctor and dietitian may recommend that you or your child:

  • Eats meals and snacks at regular intervals during the day to keep blood sugar levels steady
  • Avoids foods that are high in long-chain fatty acids, such as meat, vegetable oils, nuts, and fish
  • Adds more carbohydrate-rich foods for energy and to keep blood sugar levels steady. It's especially important to get enough carbs when energy needs are higher, such as during exercise or sickness.
  • If your child's blood sugar level drops very low, they may need to go to a hospital and get a sugar solution through a vein (IV).

Supplements for long-chain fatty acid oxidation disorders (LC-FAODs)

Medium-chain triglycerides (MCTs) are fat molecules made up of shorter carbon chains than long-chain fatty acids. They're easier for people with LC-FAODs to break down and use for energy than long-chain fatty acids. 

Taking an MCT oil supplement can prevent long-chain fats from building up in your body. Some infants with LC-FAODs may need formula with added MCTs because breast milk is too high in fat for their body to process.

Medicine for long-chain fatty acid oxidation disorders (LC-FAODs)

Triheptanoin (Dojolvi) is the only medicine approved to treat LC-FAODs. You can get it only by prescription. It contains calories and fatty acids to supplement your diet and give your body the energy you're missing. The recommended dose is up to 35% of your daily calories. It comes as a liquid that you mix with drinks or soft foods and take by mouth, or take through a feeding tube. 

Possible side effects include belly pain, diarrhea, nausea, and vomiting. 

Lifestyle changes for long-chain fatty acid oxidation disorders (LC-FAODs)

Certain things trigger LC-FAOD symptoms. You'll start to learn what sets off your flares. Common triggers are hunger, intense activity or exercise, illness, and stress.

In general, try to:

  • Avoid fasting. Don't go without food for more than eight hours. 
  • Pace yourself when you exercise or do other activities. Don't overdo it.
  • Use relaxation techniques like deep breathing, meditation, and yoga to calm down when you're stressed.
  • Take care of yourself. Eat a balanced diet, sleep well, and get all the vaccines your doctor recommends to prevent infections.

The different types of LC-FAODs progress in different ways, depending on the specific missing enzyme and the damage it causes. Generally, people with one of these conditions will have muscle and nerve damage by their late teens or early adulthood. But exactly when this happens and how severe it is will be different for different people. 

When your body doesn't break down and use fatty acids properly, it can't make enough energy for your organs to function well. Also, fatty acids can build up in and damage your organs. LC-FAODs can cause problems with your muscles, heart, eyes, and liver.

Low blood sugar

When your body can't use fat for energy, it burns stored glucose (sugar) instead. Glucose stores get depleted, causing a drop in blood sugar. Doctors call this type of low blood sugar hypoketotic hypoglycemia. It causes symptoms like sluggishness and a lack of energy, and it can be life-threatening for a baby.

Heart problems

Without fatty acids, the heart doesn't have enough energy to contract. It has to work much harder to pump blood out to the body. Just like any other muscle, the heart muscle gets larger when it works hard. An enlarged heart has even more trouble pumping. The medical term for this condition is hypertrophic cardiomyopathy. Abnormal heart rhythms are also common in people with these conditions. 

Muscle damage

Muscles use fat for energy. When fat isn't available, especially during exercise, muscles can get damaged. Doctors call this damage rhabdomyolysis. Symptoms include pain and trouble walking.

Liver damage

Liver problems are common in LC-FAODs, and they can range from mild to severe. Symptoms include jaundice, pale-colored poop, and very low muscle tone.

High ammonia levels in the blood

Ammonia is a waste product your digestive system makes when it breaks down protein. High levels of ammonia in the blood can damage the brain and spinal cord. This condition is life-threatening and needs treatment right away.

Nerve damage

Nerve damage, called neuropathy, is more common in some LC-FAODs than others. It affects around 80% of people with TFPD and 5% to 10% of those with LCHAD. Nerve damage can cause problems with speech, movement, learning, and talking.

Eye damage

The retina in the back of the eye needs energy to send visual signals to the brain. LC-FAODs can cause retinopathy – damage to the retina that could lead to vision loss.

Children and adults with LC-FAODs need to follow a specific diet and avoid things that trigger their symptoms.

LC-FAODs diet

The diet for LC-FAODs is low in fat and high in carbohydrates. Fats make up 30% to 35% of the diet. MCT oil supplements, instead of long-chain fatty acids, provide energy.           

LC-FAODs cost

Even with dietary changes, people with LC-FAODs get symptom flare-ups that require medical care, sometimes in a hospital. Costs can add up, especially when there are complications like cardiomyopathy or low blood sugar.

The average yearly health care costs for a child with an LC-FAOD is more than $17,000. It rises to nearly $44,000 when the child has a complication. Medical costs for adults with the disorder are almost $44,000 per year, and more than $94,000 with a complication.

LC-FAODs and mental health

An LC-FAOD doesn't just affect your physical health. It also has major impacts on your social life, your ability to work or go to school, and your emotional well-being. Caring for a child with one of these conditions is a difficult job that can cause a lot of stress and anxiety.

These tips can make life with an LC-FAOD easier for you or your child: 

Learn as much as you can about LC-FAODs and their treatments. Knowledge will make you feel more empowered to care for yourself or your loved one.

Get emotional support when you need it. That support can come from friends, family, a therapist, or another mental health care provider.

Join a support group. Meeting people who've been on the same journey can make you feel less alone, and like you're part of a community. Support groups are safe spaces for you to talk honestly about your experiences, learn from others, and gain valuable coping skills.

These organizations offer information, educational materials, and support for people with LC-FAODs and their families.

International Network for Fatty Acid Oxidation Research and Management (INFORM). This organization was founded by doctors and researchers. INFORM does research and educates people with FAODs and their family members about these conditions.

FOD (Fatty Oxidation Disorders) Family Support Group. The goal of this group is to provide support and information to families of people with fatty oxidation disorders.

Global Genes. This nonprofit organization connects people who have rare genetic conditions like LC-FAODs with helpful resources.

LC-FAODs are very serious conditions that cause life-threatening complications of the heart, liver, and other organs. These disorders are usually most severe when they start early in life. Newborn screening has led to earlier detection and improved outcomes. The sooner your child gets diagnosed and treated, the better their prognosis will be.         

Can long-chain fatty acid oxidation disorders (LC-FAODs) be cured?

These conditions aren't curable. But you can manage them with diet changes and supplements. 

What to expect with long-chain fatty acid oxidation disorders (LC-FAODs) 

LC-FAODs are a group of more than 20 disorders. The outcome depends on the type of disorder, when it started, and how it's treated. Your doctor will tell you what you or your child can expect.

LC-FAODs aren't preventable because they're inherited genetic disorders. But they can be detected early with newborn screening.

Long-chain fatty acid oxidation disorders (LC-FAODs) are a group of more than 20 inherited disorders that prevent the body from breaking fatty acids down into energy. Routine newborn screening can detect these conditions early, when they're most treatable. Dietary changes and supplements can help prevent complications and improve outcomes.

How do you treat LC-FAODs?

Treatment involves a diet that's low in long-chain fatty acids and high in carbohydrates, plus supplements of medium-chain triglycerides (MCTs). One medication, Dojolvi, is approved to treat LC-FAODs.

What are the symptoms of fatty acid oxidation disorders?

The specific symptoms depend on the disorder. They can include muscle weakness, low blood sugar, and an irregular heartbeat.

Are LC-FAODs curable? 

These disorders aren't curable, but they are treatable – especially when diagnosed early.