What Is Carnitine Palmitoyltransferase 1a Deficiency?

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is a rare disorder affecting how the body processes and turns energy into a type of fat called fatty acids. Specifically, it is something called an inborn error of metabolism (a genetic condition altering the body's ability to process and convert substances like fats and proteins), and this happens when something is wrong with the oxidation of long-chain fatty acids. It is caused by a mutation (change) in the CPT1A gene and produces symptoms like hypoglycaemia (low blood sugar) and issues with the liver.

This article will go into depth about CPT1A deficiency, exploring its causes, how people find out they have the deficiency, and the current management strategies.

Genetics and inheritance

Genes are made up of Deoxyribonucleic acids (DNA) and are the codes for producing different proteins in the body, including enzymes – which help with chemical reactions in the body. CPT1A deficiency occurs when there is a mutation in the CPT1A gene, leading to the production of defective CPT1A enzymes. This enzyme is critical for the energy generation that comes from fatty acids and takes place in the energy-creating mitochondria, the powerhouse of the cell.

This disorder is inherited in an “autosomal recessive” manner.  This means that each individual has two genes for the enzyme, and for a child to inherit the disorder, both parents would need to be carriers, therefore having only one copy of the mutation of the same gene, with the other gene being normal. The mutated gene is then passed on to the affected child from each parent, meaning the child now has both copies of the defective gene, causing this deficiency.  The probability of this happening is 25%, meaning that, on average, 1 in 4 of children will have this deficiency.  Genetic counselling regarding future pregnancies may be provided to couples who may have a child with the deficiency.  They can also advise on testing other members of the family.

What is the mechanism behind it?

Most of the energy production by oxidation from fatty acids happens in the mitochondria, and long-chain fatty acids cannot enter them unmodified. CPT1A codes for the liver version of the enzyme are required to be added to carnitine, allowing them to enter the mitochondria.¹   

Different mutations cause different problems with the enzyme. One mutation termed P479L is called the “Arctic variant” and is found in relatively high numbers in the Inuit population. This version does not appear to cause liver failure and has around 20% activity of the normal enzyme. Also, the “Micronesian variant” (S34P) exists, and this has been found in increasing numbers following newborn screening in Hawai’i and New Zealand, although this appears to be less harmful than other types.²  Other less common versions can be found, with different frequencies.

Most of our energy comes from glucose, a type of sugar. When the glucose level is low, the body creates energy from other sources, including fats. With the CPT1A enzyme missing, this energy from fatty acids isn’t produced in the same quantities as normal, and the glucose reserves can decrease so much that hypoglycaemia may occur.³

What signs and symptoms are there, and what else can happen?

Symptoms typically occur when the body is under stress, such as when individuals fast (not eating for a prolonged period of time) or during an illness when the demand for energy increases. This leads to a state called hypoketotic hypoglycaemia, which is low blood sugar and a low amount of ketone bodies (an alternative energy source) in the blood.

The disorder is usually picked up in early childhood, and the onset of symptoms can be rapid. 

Some symptoms include:

• Poor appetite
• Irritable mood
• Changes in behaviour
• Fever
• Diarrhoea
• Vomiting

CPT1A deficiency may cause sudden liver failure and problems with the brain and nervous system resulting from liver dysfunction (hepatic encephalopathy). It is also associated with a kidney condition called renal tubular acidosis.

As well as hypoketotic hypoglycaemia, there may be a build-up of ammonia in the blood (hyperammonaemia) and increased liver enzymes.

If left untreated, it can progress to loss of consciousness, seizures, coma and possibly death.  Learning difficulties, problems with walking and other motor skills have also been reported.³

How is it diagnosed?

Newborn screening is available in certain areas, although this does not give a diagnosis of CPT1A deficiency – instead, detecting that it may be a possibility.

Genetic tests are required for a firm diagnosis, and confirmation requires a demonstration of a mutation in the CPT1A gene or testing of the level of enzyme activity in skin cells.  Laboratory tests could also look at carnitine levels, ammonia levels, liver enzymes and ketones.⁴

What about pregnancy?

If you are pregnant with a baby who has the condition, you are at an increased risk of developing acute fatty liver during pregnancy and should be monitored for this. Symptoms start in the third trimester and can include nausea, vomiting, anorexia, and abdominal pain.⁵

How common is CPT1A deficiency?

Roughly 60 individuals have been reported to have the condition, and it occurs in males and females equally.⁴ It is more common among certain populations, including the North American Hutterite community, the Native American Inuit people and Micronesian groups in New Zealand and Hawai’i.² It may be more common in other countries but remains undetected because of the lack of a screening programme.

Management and treatment

When hypoglycaemia occurs, prompt treatment is necessary to prevent complications. This may be in the form of an intravenous (IV) infusion of dextrose, a type of sugar, to return the blood sugar levels back to normal.  If untreated, this can lead to a metabolic emergency, where the body is susceptible to both short and long-term damage.⁶ 

Prevention

To prevent hypoglycaemic episodes, individuals with the deficiency should avoid fasting. Infants should eat regularly throughout the day – in general, every 4-6 hours.³  They can also have cornstarch overnight to help provide a slow release of energy.   Fasting should last no more than 12 hours for older children and even less during times of stress to the body, such as illness or medical procedures.⁶  As children may not want or are unable to eat when ill, they may need treatment at a hospital to prevent a metabolic emergency.

A high-carbohydrate, low-fat diet is recommended. Since CPT1A deficiency affects long-chain fatty acids, a dietitian may suggest avoiding long-chain fatty acid foods, such as dairy, coconut and vegetable oil. Supplementation with certain types of fat called medium-chain triglycerides should make up part of the diet.⁷ A doctor and dietitian may give an appropriate feeding plan to follow for your child, and they should be consulted before making any dietary changes.

Affected individuals should have their liver function monitored (especially when they have gone through a period of not eating much or during times of illness), as should pregnant people who are carriers of the gene.⁷

Infection risk

A study looked at a common version of the defective gene and the risk of infection from certain diseases and found that there was an increased susceptibility. It was found to be associated with an impaired response with a type of immune cell called a neutrophil in human and mouse models.⁸

Prognosis

Adhering to the correct diet and avoiding prolonged periods of fasting means individuals with CPT1A deficiency can often have normal or near-normal lives. There is a great variation in how people are affected, and this can be influenced by what specific mutation of the gene they have.

Having repeated episodes of metabolic emergencies, however, can mean some suffer neurological impairment.⁷

There is also the risk of developmental disability.

Support groups

Since it is such a rare deficiency, there may not be specific groups dedicated to CPT1A deficiency.

There is an organisation for inherited metabolic disorders called ‘Metabolic Support UK’ that provides support worldwide for a wide range of conditions (CPT1A deficiency included). They are also involved in advocating for increased screening and the adoption of “orphan drugs” and were instrumental in the creation of EURORDIS, which helps those living with a rare disease in Europe.⁹

Summary

CPT1A deficiency is a very rare metabolic disorder usually diagnosed in childhood that alters how long-chain fatty acids are used in the liver to produce energy. A genetic mutation creates a faulty enzyme, with different mutations associated with varying severity, ranging from having no symptoms to a serious problem with the liver and nervous system called hepatic encephalopathy and possibly death. 

A low blood sugar state called hypoketotic hypoglycaemia can occur when not enough has been eaten or during illnesses.  If untreated, this can lead to a metabolic emergency and hepatic encephalopathy, potentially causing seizures, comas, future learning disabilities and death.

A dietitian may construct a high-carbohydrate, low-fat meal plan to avoid symptoms and advise on avoiding fasting. It is important to seek medical help if your child is suffering from an illness, as they may need help with feeding.

With the correct treatment, many people with this deficiency can lead normal lives, and genetic counselling is available for families. It is also important to be monitored during pregnancy if you are a carrier of the gene.  Support is available through organisations, and talking to a healthcare professional about any concerns is also available.