Short Chain Acyl CoA Dehydrogenase Deficiency
What else is it called?
- ACADS Deficiency
- Butyryl-CoA Dehydrogenase Deficiency
- Lipid-Storage Myopathy Secondary to Short Chain Acyl CoA Dehydrogenase Deficiency
- SCAD Deficiency
- SCADH Deficiency
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What causes it?
SCADD belongs to a group of conditions known as the Fatty Acid Oxidation Disorders (FOD’s). It is caused by a problem in the ACADS gene which provides the instructions needed to make an enzyme called short-chain acyl-CoA dehydrogenase. This enzyme is needed to break down a group of fats called short chain fatty acids so that they can be used for energy.
A problem in the ACADS gene means that not enough of the enzyme is produced and therefore you will be unable to break down the short chain fatty acids. These fatty acids are an important source of energy and your body needs them, especially during long periods without foods. If you are unable to break down the fatty acids, it means they cannot be used for energy. High levels of fatty acids can accumulate in the liver and muscles and ammonia and other substances can also build up in the body and blood which is harmful and leads to the symptoms of this condition. It is not fully understood why many people with SCADD do not have symptoms.
How common is it?
This condition is thought to affect approximately 1 in 35,000 to 50,000 newborns. Its prevalence has increased in recent years due to newborn screening in the USA which has detected more babies with the condition and identified many who do not have symptoms.
What are the signs and symptoms?
The signs and symptoms of this condition vary. Most people with SCADD do not show symptoms.
A sudden and severe onset of symptoms, known as a metabolic crisis, may be precipitated by certain triggers such as excessive exercise, long periods without food and illness or infection.
Symptoms of a metabolic crisis include:
- Behaviour changes
- Poor appetite/feeding
Symptoms can progress to include diarrhoea, vomiting and fever. If left untreated, crises can cause seizures and can be fatal.
You may also have the following symptoms:
- Failure to grow and gain weight at the expected rate
- Delays in reaching developmental milestones
- Enlarged liver and/or spleen
- Muscle weakness
In some cases, SCADD presents in adulthood. The adult form causes problems with the muscles and can cause muscle pain and weakness. Adults can also have episodes of nausea, vomiting and short breath. Symptoms worsen after heavy exercise.
How is it diagnosed?
This condition can be diagnosed with a specialised blood and urine tests and by measuring the enzyme activity. SCADD is routinely screened for at birth as part of the newborn screening programmes in Austria, Hungary, Iceland and the USA. Relatives of those who receive a diagnosis may also be tested as they may have the condition but not show symptoms.
Can it be treated?
There is no cure for this condition. Since in many cases there are no symptoms, treatment is not usually required. If it is necessary, you should avoid going for long periods of time without food and eat regularly as advised by your consultant. There is no specific diet to follow, but it should be a balanced diet. You may also be advised to avoid excessive exercise or exertion. You will be given an emergency regimen to follow should a metabolic crisis occur.
Do my family need to be tested?
Humans have chromosomes composed of DNA. Genes are pieces of DNA that carry the genetic instruction. Each chromosome may have several thousand genes. We inherit particular 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.
This is an inherited condition. There is nothing that could have been done to prevent it.
Everyone has a pair of genes that are needed to produce the SCAD enzyme. If you have this condition, neither of these genes works correctly. You will inherit one non-working gene from each parent.
Parents of children with this condition are known as carriers. Carriers do not have the disorder because the other gene of this pair is working correctly.
When both parents are carriers, in each pregnancy the risk to the baby is as follows:
- 25% chance (1 in 4) of developing the condition
- 50% chance (1 in 2) for the baby to be a carrier
- 25% chance (1 in 4) for the baby to have two working genes and neither have the condition, nor be a carrier.