VLCADD is an inherited fatty acid oxidation disorder caused by deficiency or ineffective functioning of an enzyme called "very long-chain acyl-CoA dehydrogenase" (VLCAD). Without this enzyme, certain fats called "very long-chain fatty acids" cannot be broken down properly.
Fatty acids are a major source of energy for the heart and muscles. During periods of fasting, fatty acids are also an important energy source for the liver and other tissues. When very long-chain fatty acids are not metabolized properly, they cannot be converted to energy resulting in low blood sugar level (hypoglycaemia) and lethargy. At the same time, other toxic metabolites may also build up inside cells and damage multiple organs including the liver, heart and muscles.
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Very Long-Chain Acyl-CoA Dehydrogenase Deficiency (VLCADD)
Our body breaks down fats from food into fatty acids when we eat, and breaks down fats from the body stores into fatty acids during prolonged fasting and stress. When functioning normally, our body will produce Very Long Chain Acyl-CoA Dehydrogenase to break down the long chain and very long chain fatty acids for energy made for cells. In people with VLCADD, the Very Long Chain Acyl-CoA Dehydrogenase is either missing or not working properly, making the long chain and very long chain fatty acids unable to be metabolised properly. As a result, energy made for cells is disrupted, causing serious health problems.
Everybody has two copies of genes, one from each parent, which tell the body how to make specific enzymes.
Very long-chain acyl-CoA dehydrogenase deficiency is an autosomal recessive disease. Only when babies inherit two faulty copies of the gene for very long-chain acyl-CoA dehydrogenase deficiency from parents, the enzyme made does not work properly or is not even made at all.
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Autosomal recessive inheritance
In autosomal recessive diseases, people with two faulty copies of gene (one from father and one from mother) will develop symptoms. People with only one faulty copy of gene are normal and they are called disease carriers.
VLCADD is inherited in autosomal recessive manner. If both parents are VLCADD carriers, for each pregnancy (no matter it is a baby boy or girl), there is a 25% (1 in 4) chance that the child has 2 copies of normal gene (who is not affected), a 50% (1 in 2) chance that the child has one normal and one faulty gene who is a carrier like the parents, and a 25% (1 in 4) chance that the child has two copies of faulty gene who is at risk for VLCADD.
VLCADD can be very variable causing mild effects in some patients and more serious problems in others. Symptoms may start in infancy or later in adulthood.
Some VLCADD babies diagnosed and treated early through newborn screening may not develop signs or symptoms of the disease.
However, if VLCADD is not diagnosed early, some patients may develop problems in early infancy or childhood with episodic bouts of illness called metabolic crisis.
Other problems that some VLCADD patients may have include:
Metabolic paediatricians and dieticians will work together to give expert advice and care to the babies with VLCADD. When necessary, treatment is usually needed throughout the life. The goal of treatment is to prevent metabolic crisis and accumulation of toxic metabolites.
It is important that babies with VLCADD be fed regularly and do not go for long periods without eating.
Treatment for VLCADD can be varied in different patients. Certain treatment such as a special diet or medication like L-carnitine may be advised for some patients but not the others. When indicated, L-carnitine is a safe and natural substance that helps body cells make energy. It also helps the body get rid of harmful wastes.
Also very important is to discuss and design a care plan with your doctor and dietician beforehand, to let you know how to care for and provide extra sugary foods during illness or when your baby is not feeding well to prevent a metabolic crisis.
If you are worried that your baby is ill, it is important to follow medical advice. Bring your baby to your local accident and emergency department immediately. Take any information that you have been given about VLCADD, including this pamphlet, to the hospital with you.
For general queries on Newborn Screening Programme for Inborn Errors of Metabolism, please call 5741 4280 (Department of Clinical Genetics, Hospital Authority)
July 2024
Hospital Authority