What is carnitine palmitoyltransferase deficiency?

Carnitine palmitoyltransferase (CPT) deficiency is a very rare condition that causes muscle weakness and other symptoms. It happens because of a problem with one of two enzymes, CPT1 or CPT2. Enzymes are substances in the body that help cause chemical reactions.

CPT enzymes help get fatty acids into cells to use for energy. They are especially important for certain cells, such as muscle cells. With CPT deficiency, cells that rely on fatty acids for energy may start to work poorly. This leads to symptoms, such as muscle weakness and heart or liver problems. CPT deficiency can happen in men, women, and children of all ages.

There are 2 main types of CPT deficiency:

• CPT 1 deficiency. This type causes problems with the CPT1 enzyme. The CPT1 enzyme helps get fatty acids inside your cells.

• CPT 2 deficiency. This type causes problems with the CPT2 enzyme. The CPT2 enzyme helps make sure your body can use fatty acids once they are inside your cells.

There are 3 subtypes of CPT2 deficiency:

• Myopathic form (most common)

• Severe infantile hepatocardiomuscular form

• Lethal neonatal form

Babies with the lethal neonatal form of CPT2 usually die within the first few weeks to months of life. Babies with the severe infantile form may live somewhat longer but likely have heart problems and sudden death. The myopathic form is milder. Most people with this form have a normal life expectancy.

What causes carnitine palmitoyltransferase deficiency?

CPT deficiency is caused by an abnormal gene. A problem with the gene might cause the CPT1 or CPT2 enzymes to be missing or not work normally.

Who is at risk for carnitine palmitoyltransferase deficiency?

You or your child may be at risk for CPT deficiency if it runs in your family. In most cases, a person needs to inherit an abnormal gene from both parents.

What are the symptoms of carnitine palmitoyltransferase deficiency?

Children with CPT deficiency tend to show symptoms within the first few years of life. But in some cases, symptoms may begin as an adult. 

CPT deficiency can cause: 

• Symptoms of low blood sugar (hypoglycemia)

• Liver problems, such as an enlarged liver

• Nervous system damage, from liver problems

• Coma and sudden death

Symptoms can happen a bit differently in each person. Symptoms may be mild to severe. Between episodes, people with CPT1 or CPT2 deficiency may not have any symptoms.

The myopathic form of CPT2 deficiency causes milder symptoms. It does not cause heart or liver problems. Symptoms may begin any time up to age 60. Symptoms can appear with skipping meals, a lot of exercise, or illness. Symptoms may include:

• Symptoms of low blood sugar (hypoglycemia)

• Temporary muscle pain

• Muscle breakdown

• Muscle weakness

In the lethal neonatal form, symptoms usually begin within a few days after birth. In the severe infantile hepatocardiomuscular form, symptoms begin in the first year of life. These forms can also cause:

• A weakened heart (cardiomyopathy)

• Abnormal heart rhythms

• Facial abnormalities

• Respiratory problems

• Abnormalities of the brain and kidneys (in the lethal neonatal form)

• Muscle weakness (in the severe infantile hepatocardiomuscular form)

How is carnitine palmitoyltransferase deficiency diagnosed?

The condition may be diagnosed by a neurologist or geneticist. An infant may be diagnosed through standard newborn screening tests.

The process to diagnose CPT deficiency starts with a medical history and a physical exam. Your healthcare provider will ask about your symptoms and past medical conditions. They may also ask about your family’s medical history. The physical exam may include a neurological exam. Tests may also be done, including:

• Blood tests. These are done to check the levels of acylcarnitine in the blood. And they check for enzymes in the blood that can show liver disease.

• Urine test. This test looks for ketones. It also looks for myoglobin in the urine to check for muscle breakdown.

• Exercise tests. These help identify the type of metabolic problem.

• Genetic test. This kind of test can confirm CPT deficiency.

• Heart tests. Tests, such as echo cardiography, can show if the heart is affected.

How is carnitine palmitoyltransferase deficiency treated?

A change in diet is the main treatment for CPT deficiency. This diet must stay away from relying on fats for energy. It should provide a high amount of carbohydrates. It should contain a low amount of fats and protein. It’s also important to eat often. This can prevent low blood sugar. It can also prevent the body using fats for energy. And you should stay away from things that may set off symptoms. These may include skipping meals, exposure to cold, stress, and a lot of exercise.

The medicine bezafibrate may help to reduce muscle pain and weakness for people with the myopathic form of CPT2.

What are possible complications of carnitine palmitoyltransferase deficiency?

The adult myopathic form of CPT2 deficiency can sometimes cause kidney failure. This happens when muscle breaks down during exercise, a condition known as rhabdomyolysis. This creates a chemical that can damage the kidneys. You might need extra IV fluids or dialysis to prevent or treat this.

Heart weakness (cardiomyopathy) is a serious possible complication of some forms of CPT deficiency. A heart that is weak may not be able to pump blood as well. This can lead to symptoms, such as swelling and shortness of breath. Untreated heart weakness may lead to death early in life.

Liver problems are another serious possible complication. Liver problems can lead to episodes of low blood sugar (hypoglycemia), often set off by an infection. Untreated hypoglycemia can cause brain damage, leading to coma and death.

What can I do to prevent carnitine palmitoyltransferase deficiency?

If the condition runs in your family, you may want to see a genetic specialist before you have a baby. Genetic testing can be done to find out your risk of passing the disease to your child.

If you do have the abnormal gene for the condition, you have choices. If you use in vitro fertilization, the embryos can be tested for the disease. Amniocentesis can also be used to test for the condition in early pregnancy.

When should I call my healthcare provider?

Call your healthcare provider right away if you think you are having an episode of symptoms. This includes weakness or muscle pain following exercise.

For some people, advocacy organizations can offer information and support that help patients and families manage this condition. The National Institutes of Health Genetic and Rare Disease Information Center (GARD) provides the names of patient advocacy organizations. The organizations are not endorsed by GARD but are made available for informational purposes only.

Key points about carnitine palmitoyltransferase deficiency

• CPT deficiency is a condition that causes muscle weakness and other symptoms. It happens because of a problem with one of two enzymes, CPT1 or CPT2.

• The condition is caused by an abnormal gene.

• Symptoms can include muscle pain and weakness.

• If the condition runs in your family, you may want to see a genetic specialist before you have a baby.

• A low-fat diet is the main treatment for CPT deficiency.

• You may need to stay away from activities that can set off symptoms, like skipping meals or exercising a lot.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

• Know the reason for your visit and what you want to happen.

• Before your visit, write down questions you want answered.

• Bring someone with you to help you ask questions and remember what your provider tells you.

• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.

• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are.

• Ask if your condition can be treated in other ways.

• Know why a test or procedure is recommended and what the results could mean.

• Know what to expect if you do not take the medicine or have the test or procedure.

• If you have a follow-up appointment, write down the date, time, and purpose for that visit.

• Know how you can contact your healthcare provider if you have questions, especially after office hours or on weekends.