This is the first part of our mini-series about the condition based on our patient booklet “Fast Facts for Patients: Long-Chain Fatty Acid Oxidation Disorders”. This article explains what fats and fatty acids are, what they do, and what long-chain fatty acid oxidation disorders are.

First, the Facts

  • Long-chain fatty acid oxidation disorders (LC-FAODs) are rare, inherited conditions.
  • With an LC-FAOD, the body has trouble breaking down fat for energy, which can lead to symptoms such as low blood sugars, muscle pain/weakness, and heart problems.
  • LC-FAODs are diagnosed by newborn screening or symptoms later in life.
  • Management includes a specialized nutrition plan, and prevention of fasting, especially during illness.
  • A person with an LC-FAOD can live a full, active and healthy life with lifestyle changes and close coordination with, and support from, an expert healthcare team.

Fats and Fatty Acids

Fat as an Energy Source

Our bodies need energy to keep muscles, organs and normal processes working. The three types of food that provide energy are carbohydrates (in the form of sugars and starches), protein and fats. The body stores fat under the skin and around the organs so that it can be used to provide energy when needed.

Fatty Acids Are Building Blocks

Fats are made up of building blocks called fatty acids. Fatty acids are usually joined in groups of three (tri) to a glycerol backbone – this is called a triglyceride. Each fatty acid is made up of a chain of carbon atoms with hydrogen atoms attached.

Fatty acids are usually joined in groups of three (tri) to a glycerol backbone – this is called a triglyceride.

Fats enter the body from our diet. Fatty acids are released from triglycerides. They are either stored as fat or used as a source of energy in the body.

The number of carbon atoms varies between different fatty acids; for example:

  • Palmitic acid has 16 carbons and is found in palm oil.
  • Oleic acid has 18 carbons and is found in olive oil.
  • Arachidonic acid has 20 carbons and is found in meat and dairy products.

Fatty Acids for Energy

When the body needs to use fat as an energy source, it breaks down the triglyceride and releases fatty acids. These fatty acids then travel in the blood to the muscles and organs where they can be used for energy.

Introducing Beta Oxidation

Once the fatty acids are in the muscle or organ where they will be used for energy, they go through a complicated process called beta oxidation. This takes place in mitochondria, which are specialized areas in cells.

Fatty acids and beta oxidation.

The body takes energy from fatty acids.

What is an enzyme?

Long-Chain Fatty Acid Oxidation Disorders

Each fatty acid contains a chain of carbons. The length of this chain varies, with most fatty acids having between 4 and 24 carbons.

Short-chain, medium-chain and long-chain fatty acids.

Enzymes are needed to move long-chain fatty acids into the mitochondria and process them for energy. LC-FAODs happen when one of the enzymes involved in breaking down long-chain fatty acids for energy is not made or is not working properly.

As a result, the body is unable to use these fatty acids for energy in the usual way. This can lead to problems with energy supplies. Not being able to use energy from stored fat can cause harmful effects. Having partially digested fatty acids in the body may also cause problems.

LC-FAODs are named according to the enzyme that is affected. The most common types of LC-FAOD are:

  • Carnitine palmitoyltransferase 1 or CPT1 deficiency (sometimes written as CPT I)
  • Carnitine acylcarnitine translocase or CACT deficiency
  • Carnitine palmitoyltransferase 2 or CPT2 deficiency (sometimes written as CPT II)
  • Very-long-chain acyl-CoA dehydrogenase or VLCAD deficiency
  • Long-chain 3-hydroxy-acyl-CoA dehydrogenase or LCHAD deficiency
  • Trifunctional protein or TFP deficiency.

The affected enzymes are important for either:

  • the carnitine shuttle, which moves the long-chain fatty acids into the mitochondrion, or
  • the long-chain beta-oxidation spiral, which breaks down long-chain fatty acids into shorter and shorter pieces, two carbons at a time.

The two carbons removed in each round of beta oxidation form a molecule called acetyl-CoA, which then enters another energy producing cycle in the mitochondrion.

Long-chain fatty acid oxidation disorders are named according to the enzyme that is affected.


Please check out the other posts of our series here:


Information based on Fast Facts for Patients: Long-Chain Fatty Acid Oxidation Disorders (Karger, 2021).

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