This is the third 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 a gene is and details genetic testing as well as counseling.

What Is a Gene?

A gene is a section of DNA that tells the body how to make a specific protein – in the case of long-chain fatty acid oxidation disorders (LC-FAODs), the protein is an enzyme.

Genetic Testing

LC-FAODs are inherited genetic disorders. They happen because the gene that carries the instructions for making the specific enzyme has a misprint or change. This means that not enough of the enzyme is made or it is made incorrectly and does not work properly.

Your doctor may suggest genetic testing to identify the genetic changes that are present. The test is carried out on a blood sample.

There are many different genetic changes that can lead to LC-FAODs. The name of the gene that is altered or changed in each of the LC-FAODs is shown in the table below.

Name of the altered or changed gene in each of the long-chain fatty acid oxidation disorders

We have two copies of most of our genes – one copy from each of our biological parents. A person will have an LC-FAOD only if both copies of the gene passed on from their parents have the genetic change. If only one parent passes on a copy with a change, the other copy of the gene may be able to make a working enzyme. If this happens, the person will not have an LC-FAOD but is said to be a carrier. A carrier can pass the genetic change on to their child. The illustration shows the different combinations – the pattern is called recessive inheritance.

How Many People Are Affected?

LC-FAODs are very rare. Overall, it is estimated that 1 newborn is identified with a fatty acid oxidation disorder in every 9,300 babies. The conditions tend to be more common in European countries and populations with European ancestry. In contrast, they are much less common in Asian countries. Some disorders are particularly common in specific groups: for example, CPT1 deficiency seems to occur more often in Inuit people living in northern Canada. VLCAD deficiency is the most common LC-FAOD. It is identified in 1 in 30,000 to 1 in 100,000 newborns, depending on the population.

Transmission of the genetic change: carriers, affected and those unaffected

Genetic Counseling

Genetic counseling involves discussing the likelihood that the genetic change that you carry would be passed on to your children.

If you are a parent of a child with an LC-FAOD, you most likely were not aware that you carried the genetic change. A health professional or geneticist will talk to you about the likelihood of other or future children being affected.

You and your partner may also be offered carrier testing. Blood samples will be sent to the laboratory, and the gene will be checked to see if it has the same genetic change as your child has.

Prenatal Diagnosis

Prenatal diagnosis is a way of checking during pregnancy whether a baby carries two copies of the genetic change. Your doctor or geneticist will talk to you about what is involved and the information that the test will provide.

In vitro fertilization so that the genetic make-up of the embryo can be checked before implantation may also be a possibility. Again, this is something to discuss with your healthcare team.


If you are a woman with an LC-FAOD and you become pregnant, you may require closer monitoring during the pregnancy. There may be changes in your dietary recommendations or supplements.

You should notify your metabolic care team if you are planning a pregnancy and as soon as you know that you are pregnant.


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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