MCADD is an inherited fatty acid oxidation disorder caused by deficiency or ineffective functioning of an enzyme called "medium-chain acyl-CoA dehydrogenase" (MCAD). Without this enzyme, certain fats called "medium-chain fatty acids" cannot be metabolized.
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. People with MCADD rely on glucose for main source of energy. When glucose has been used up, for example after skipping a meal or no eating for a long time, the body will try to use fat for energy but without success. This can cause low blood sugar level (hypoglycaemia). At the same time, medium-chain fatty acids or other partially metabolized fatty acids may build up in tissues and cause damage to the body.
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Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCADD)
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 Medium Chain Acyl-CoA Dehydrogenase to break down the medium chain fatty acids for energy made for cells. In people with MCADD, the Medium Chain Acyl-CoA Dehydrogenase is either missing or not working properly, making the medium 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.
Medium-chain acyl-CoA dehydrogenase deficiency is an autosomal recessive disease. Only when babies inherit two faulty copies of the gene for medium-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.
MCADD deficiency is inherited in autosomal recessive manner. If both parents are MCADD deficiency 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 MCADD deficiency.
With prompt and careful treatment nowadays, children with MCADD usually have healthy lives with normal growth and development.
Most MCADD babies diagnosed and treated early through newborn screening may never develop signs or symptoms of the disease.
However, if MCADD is not diagnosed early, patients may develop problems in early infancy or childhood with episodic bouts of illness called metabolic crisis.
Metabolic paediatricians and dieticians will work together to give expert advice and care to the babies with MCADD. The goal of treatment is to prevent metabolic crisis and accumulation of toxic metabolites.
Babies with MCADD can usually eat a normal diet. However, it is very important to observe the following:
avoid long periods without eating during the newborn and infancy period even when baby is well. The length of time MCADD patients can go without eating varies depending on their age; generally speaking, the younger they are, the more frequent they need to be fed.
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 MCADD, 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