CUD is an inherited fatty acid oxidation disorder due to inadequate or dysfunction of "carnitine transporter" resulting in failure of carnitine reabsorption from the kidney leading to the lack of carnitine inside the cells.
Carnitine, a natural substance acquired mostly through the diet, is used by the cells to process fats and produce energy.
If there is inadequate carnitine intracellularly, long chain fatty acids, predominantly oxidized in the mitochondria of the cells, are unable to be completely broken down resulting in failure of energy production leading to muscle weakness and low blood glucose level (hypoglycaemia). Other toxic metabolites may also build up inside the cells and damage multiple organs including the liver, the heart and the muscles.
Other names for carnitine uptake deficiency (CUD) include:
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Carnitine Uptake Deficiency (CUD)
Our body breaks down fats from food into fatty acids when we eat, and breaks down fats from body stores into fatty acids during prolonged fasting and stress. Most fatty acids especially long chain fatty acids need to be carried to mitochondria by a protein called carnitine through a multi-step process. When functioning normally, our body will produce carnitine transporter enzyme to transport carnitine to our cells, and then help long chain fatty acids to be transported into mitochondria for energy production. In people with CUD, the carnitine transporter is either missing or not working properly. Fatty acids cannot enter mitochondria and be used to make energy without enough carnitine in the cell. As a result, energy production is disrupted and metabolites build up in the body to harmful levels, causing serious health problems.
Everybody has two copies of genes, one from each parent, which tell the body how to make specific enzymes.
Carnitine uptake deficiency is an autosomal recessive disease. Only when babies inherit two faulty copies of the gene for carnitine uptake 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. CUD is inherited in autosomal recessive manner.
If both parents are CUD 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 CUD.
With prompt and careful treatment nowadays, children with CUD can have healthy lives with normal growth and development. Many CUD babies diagnosed and treated early through newborn screening may never develop signs or symptoms of the disease. However, if CUD is not diagnosed early, patients may develop problems in early infancy or childhood with episodic bouts of illness called metabolic crisis.
Other problems that some CUD patients may have include:
Metabolic paediatricians and dieticians will work together to give expert advice and care to your baby. When necessary, treatment is usually needed throughout the life.
The goal of treatment is to prevent accumulation of toxic metabolites and metabolic crisis. It is important that babies with CUD be fed regularly and do not go for long periods without eating.
Specific treatment for this condition includes L-carnitine which is a safe and natural substance that helps the body cells to make energy and get rid of harmful wastes. It is usually a lifelong treatment for most CUD patients.
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 CUD, 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