Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency is a rare condition that prevents the body from converting certain fats to energy, particularly during periods without food (fasting).

Signs and symptoms of LCHAD deficiency typically appear during infancy or early childhood. Many affected infants have feeding difficulties, such as an extreme dislike of certain foods or of eating at all (food or feeding aversion), nausea, and vomiting. Other signs and symptoms include lack of energy (lethargy), low blood glucose (hypoglycemia), weak muscle tone (hypotonia), delayed development of milestones, liver problems, and abnormalities in the light-sensitive tissue at the back of the eye (retina). Affected individuals can have impaired vision or difficulty seeing things far away (myopia) or in low light (night blindness). These vision problems worsen over time. Later in childhood, people with this condition may experience muscle pain, breakdown of muscle tissue (rhabdomyolysis), and a loss of sensation in their arms and legs (peripheral neuropathy). Infants and children with LCHAD deficiency are also at risk of serious heart problems, such as a weakened heart (cardiomyopathy) and heart failure; breathing difficulties; coma; and sudden death.

Problems related to LCHAD deficiency can be triggered when the body is under stress, for example during periods of fasting, illnesses such as viral infections, or weather extremes. This disorder is sometimes mistaken for Reye syndrome, a severe disorder that may develop in children while they appear to be recovering from viral infections such as chicken pox or flu. Most cases of Reye syndrome are associated with the use of aspirin during these viral infections.

Variants (also known as mutations) in the HADHA gene cause LCHAD deficiency. The HADHA gene provides instructions for making part of an enzyme complex called mitochondrial trifunctional protein. This enzyme complex functions in mitochondria, the energy-producing centers within cells. As the name suggests, mitochondrial trifunctional protein contains three enzymes that each perform a different function. This enzyme complex is required to break down (metabolize) a group of fats called long-chain fatty acids. Long-chain fatty acids are found in foods such as milk and certain oils. These fatty acids are stored in the body's fat tissues. Fatty acids are a major source of energy for the heart and muscles. During periods of fasting, fatty acids are also an important energy source for the liver and other tissues.

Variants in the HADHA gene that cause LCHAD deficiency disrupt one of the functions of this enzyme complex. These variants prevent the normal processing of long-chain fatty acids from food and body fat. As a result, these fatty acids are not converted to energy, which can lead to some features of this disorder, such as lethargy and hypoglycemia. Long-chain fatty acids or partially metabolized fatty acids may also build up and damage the liver, heart, muscles, and retina. This abnormal buildup causes the other signs and symptoms of LCHAD deficiency.

Normal Function

The HADHA gene provides instructions for making part of an enzyme complex called mitochondrial trifunctional protein. This enzyme complex functions in mitochondria, the energy-producing centers within cells. Mitochondrial trifunctional protein is made of eight parts (subunits). Four alpha subunits are produced from the HADHA gene, and four beta subunits are produced from the HADHB gene. As the name suggests, mitochondrial trifunctional protein contains three enzymes that each perform a different function. The alpha subunits contain two of the enzymes, known as long-chain 3-hydroxyacyl-CoA dehydrogenase and long-chain 2-enoyl-CoA hydratase. The beta subunits contain the third enzyme. These enzymes are essential for fatty acid oxidation, which is the multistep process that breaks down (metabolizes) fats and converts them to energy.

Mitochondrial trifunctional protein is required to metabolize a group of fats called long-chain fatty acids. Long-chain fatty acids are found in foods such as milk and certain oils. These fatty acids are stored in the body's fat tissues. Fatty acids are a major source of energy for the heart and muscles. During periods of fasting, fatty acids are also an important energy source for the liver and other tissues.

Health Conditions Related to Genetic Changes

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency

Researchers have identified several HADHA gene mutations that cause long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency. These mutations decrease the long-chain 3-hydroxyacyl-CoA dehydrogenase enzyme activity of mitochondrial trifunctional protein. (The protein's other enzyme activities remain normal or nearly normal.) Many of the HADHA mutations change one of the protein building blocks (amino acids) used to make the alpha subunit. The most common mutation replaces the amino acid glutamic acid with the amino acid glutamine at position 474 in the alpha subunit. This mutation is written as Glu474Gln or E474Q. The Glu474Gln mutation and other amino acid replacements probably alter the structure of the alpha subunit, preventing it from functioning normally. Other HADHA mutations result in an abnormally short, nonfunctional version of the alpha subunit.

With a shortage (deficiency) of functional alpha subunits, long-chain fatty acids cannot be metabolized and processed. As a result, these fatty acids are not converted to energy, which can lead to some features of LCHAD deficiency, such as lack of energy (lethargy) and low blood glucose (hypoglycemia). Long-chain fatty acids or partially metabolized fatty acids may also build up and damage the liver, heart, muscles, and light-sensitive tissue at the back of the eye (retina). This abnormal buildup causes the other signs and symptoms of LCHAD deficiency.

Mitochondrial trifunctional protein deficiency

Researchers have identified several HADHA gene mutations that cause mitochondrial trifunctional protein deficiency. These mutations reduce all three enzyme activities of mitochondrial trifunctional protein. Some of these mutations result in abnormally short, nonfunctional alpha subunits and lead to decreased levels of mitochondrial trifunctional protein. Other mutations replace one amino acid with another amino acid in the alpha subunit, which probably alters the subunit's structure and disrupts all three functions of the enzyme complex.

When mitochondrial trifunctional protein activity is lost, long-chain fatty acids cannot be metabolized and processed. As a result, these fatty acids are not converted to energy, which can lead to some features of this disorder, such as lethargy and hypoglycemia. Long-chain fatty acids or partially metabolized fatty acids may build up in tissues and damage the liver, heart, and muscles. This abnormal buildup causes the other signs and symptoms of mitochondrial trifunctional protein deficiency.

Other disorders

In a small number of cases, HADHA mutations appear to increase a woman's risk of developing two serious liver disorders during pregnancy, known as acute fatty liver of pregnancy (AFLP) and HELLP syndrome. AFLP begins with abdominal pain and can rapidly progress to liver failure. HELLP stands for hemolysis (the breakdown of red blood cells), elevated liver enzyme levels, and low platelets (cells involved with blood clotting).

A woman is more likely to have AFLP or HELLP syndrome if she has a mutation in one copy of the HADHA gene and the fetus she carries has two copies of a HADHA mutation, particularly the Glu474Gln mutation. Little is known about the relationship between HADHA mutations and liver problems in the mother during pregnancy. One possibility is that partially metabolized long-chain fatty acids produced by the fetus or placenta accumulate in the mother and are toxic to her liver. In very rare cases of maternal liver disease, the mother has one copy of an altered HADHA gene and the fetus is not affected. In these cases, the role of the mother's HADHA mutation in liver disease is unclear.

Other Names for This Gene

• ECHA_HUMAN
• GBP
• hydroxyacyl dehydrogenase, subunit A
• hydroxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase/enoyl-CoA hydratase (trifunctional protein), alpha subunit
• hydroxyacyl-Coenzyme A dehydrogenase/3-ketoacyl-Coenzyme A thiolase/enoyl-Coenzyme A hydratase (trifunctional protein), alpha subunit
• LCEH
• LCHAD
• long-chain hydroxyacyl-CoA dehydrogenase
• mitochondrial trifunctional protein, alpha subunit
• MTPA

Genomic Location

LCHAD deficiency is a genetic condition. Babies inherit it from their biological (birth) parents.

• LCHAD deficiency is an autosomal recessive condition. Babies inherit the condition when each parent passes down a nonworking HADHA gene to their baby. Only babies with two nonworking HADHA genes—one from the mom and one from the dad—have this condition.
  • People with one working copy and one nonworking copy of the HADHA gene are called carriers.
  • Carriers do not have or develop the condition. However, they may pass down a nonworking copy of the gene to their children.
  • If two parents are carriers of a nonworking copy of the HADHA gene, they have a 1 in 4 chance of having a child with LCHAD deficiency.
  • Carriers for LCHAD deficiency often do not know they are carriers before having a child with the condition. In most cases, families have no history of the condition until the birth of a child with LCHAD deficiency.
  • Parents who already have a child with LCHAD deficiency still have a 1 in 4 chance of having another child with LCHAD deficiency. This 1 in 4 chance stays the same for all future children.
• Genetic counselors and medical geneticists can help families learn about this condition and the chance of having children with it.

Signs of LCHAD deficiency can vary widely and may appear anytime from infancy to adulthood. Common illnesses, like a cold or flu, or going a long time without food can trigger symptoms.

Signs of the condition may include the following:

• Problems feeding
• Weak muscle tone (hypotonia)
• Tiredness or lack of energy (lethargy)
• Enlarged liver (hepatomegaly)
• Eye problems (retinopathy)
• Heart problems (cardiomyopathy)
• Low blood sugar (hypoglycemia)

Newborn screening for LCHAD deficiency is done using a small amount of blood collected from your baby’s heel. During screening, a special machine measures how much of certain substances (called acylcarnitines) are in your baby’s blood. Your body produces these substances when it makes energy from fats. Babies with high levels of these substances might have LCHAD deficiency.

If your baby has LCHAD deficiency, this condition could have caused their mother to experience health problems during the pregnancy. If the baby's mother had acute fatty liver of pregnancy (AFLP) or hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome, screening your baby for LCHAD deficiency is even more important.

What Happens After an Out-of-Range Screening Result?

If your baby’s blood spot screening result for LCHAD deficiency is out-of-range, your baby’s health care provider will contact you. Together, you will discuss next steps and follow-up plans.

An out-of-range screening result does not mean that your baby definitely has the condition. It does mean that your baby needs more follow-up testing.

Your baby may need the following tests after an out-of-range screening result:

• Blood and/or urine tests
• Genetic testing using a blood sample

You should complete any recommended follow-up testing as soon as possible. Babies with this condition can have serious health problems if they are not diagnosed and treated quickly.

False-positive newborn screening results for this condition are rare. However, certain medications, like carnitine supplements, may affect the results of screening.

Newborn screening helps babies lead healthier lives. If your baby has an out-of-range result, follow up with your health care provider quickly. It is important to follow their instructions. Your baby may need to get treatment right away, even if they are not showing signs or symptoms. In some cases, your baby’s health care provider may decide it is best to watch (monitor) your baby to decide next steps. Careful monitoring and early treatment will help your baby stay as healthy as possible.

It is important to talk to your health care provider about which treatment(s) are best for your baby. The goal of treatment is to prevent the health problems caused by this condition.

Treatments may include the following:

• Regular and frequent meals and snacks
• Diet high in carbohydrates and low in fat
• Medium chain triglyceride (MCT) oil to help give the body fats it can break down
• L-carnitine supplements to help the body break down fats
• People with LCHAD deficiency must be very careful if they get sick and have vomiting or diarrhea, or do not want to eat. They may need emergency care to prevent low blood sugar levels.

Children who receive early and ongoing treatment for LCHAD deficiency can have healthy growth and development. Continuing care is needed for problems that occur later in affected people (muscle and vision problems).

The incidence of LCHAD deficiency is unknown. One estimate, based on a Finnish population, indicates that 1 in 62,000 pregnancies is affected by this disorder. In the United States, the incidence is probably much lower.