Very-Long Chain Acyl CoA Dehydrogenase Deficiency
What else is it called?
- Acyl-CoA dehydrogenase very long chain deficiency
- Very long-chain acyl coenzyme A dehydrogenase deficiency
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What causes it?
VLCAD deficiency is caused by mutations (changes) in the ACADVL gene. This gene encodes (converts) an enzyme that is responsible for the break-down of a group of fats called very long-chain fatty acids. Changes in the ACADVL gene cause a decrease in the levels of this enzyme which stops the proper breakdown of these fats.
Very long-chain fatty acids are an important source of energy, mainly for the heart and muscles. Therefore, individuals with VLCAD have symptoms such as lethargy (tiredness) and hypoglycaemia (low blood sugar). The fats that are not broken down properly can build up and damage the heart, liver and muscles.
How common is it?
The exact number of individuals affected by the disorder is currently unknown. Estimates suggest that the disorder may affect 1 in 40,000 to 120,000 people.
What are the signs and symptoms?
Symptoms of VLCAD can start anytime between infancy and adulthood.
- Sleeping longer or more often
- Behavior changes
- Muscle weakness (hypotonia)
- Poor appetite
- Low blood sugar (hypoglycaemia)
Most of the time these signs occur when the patient eats food that their body cannot break down. Signs and symptoms can also be triggered by fasting, illnesses and infection.
Less common symptoms:
- High liver enzymes
- Enlarged liver (Hepatomegaly)
- Abnormally low body temperature (hypothermia)
- Jaundice (yellow tinge of the skin and whites of the eyes)
- Difficulties breathing
- Small for gestational age (low birth weight)
- Ventricular septal defect (Hole in heart wall separating two lower heart chambers)
How is it diagnosed?
A diagnosis of VLCAD deficiency may be discovered through an abnormal newborn screen or a number of signs and symptoms. Testing for VLCAD is included in newborn screening in the United States however it is not currently part of the new-born screening in the UK.
Additional testing is then carried out to confirm the diagnoses through specialized blood, urine, skin cells, muscle and liver tissue tests. Another way to confirm the diagnosis is to carry out genetic testing in order to detect mutations (changes) in the ACADVL gene.
Can it be treated?
Treatment of VLCAD is in the form of a restricted diet. Patients need to avoid fats that they cannot break down. The patients should also eat more often to avoid many of the signs mentioned above. Please be noted that any dietary changes require specialist dietitian’s advice and monitoring.
Individuals with VLCAD often also need dietary supplements. Medium Chain Triglyceride oil is often used for VLCAD patients. The oil contains medium chain fatty acids which are fats that the body of patients can break down. Be sure to talk to a doctor before using any supplements.
When treated early, babies with VLCAD can have healthy growth and development. However, treatment needs to continue throughout life.
Without treatment, babies with VLCAD usually die young. It is important to treat VLCAD. When left untreated it can cause breathing problems, seizures, coma or brain damage.
Do my family need to be tested?
Very-Long Chain Acyl CoA Dehydrogenase Deficiency is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents.
The pattern of inheritance of Very-Long Chain Acyl CoA Dehydrogenase Deficiency is autosomal recessive. This means that carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with Very-Long Chain Acyl CoA Dehydrogenase Deficiency are carriers.
When both parents are carriers, the risk to the baby in each pregnancy is
- 25% chance (1 in 4) of developing the condition
- 50% chance (1 in 2) for the baby to be a carrier of the condition
- 25% chance (1 in 4) for the baby to have two working genes and neither have the condition nor be a carrier
Genetic counselling can be requested to get a full explanation.