MTPD is an inherited fatty acid oxidation disorder caused by deficiency or ineffective functioning of three enzymes called “long-chain enoyl-CoA hydratase, long-chain 3-hydroxyacyl-CoA dehydrogenase and long-chain 3-ketoacyl-CoA thiolase” (MTP). Without these enzymes, certain fats called “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 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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Multiple Trifunctional Protein deficiency (MTPD)
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 for energy production. Mitochondrial Trifunctional Protein has three enzymes that converts specific types of fatty acids namely long-chain fatty acids into energy. In people with MTPD, long-chain enoyl-CoA hydratase, long-chain 3-hydroxyacyl-CoA dehydrogenase and long-chain 3-ketoacyl-CoA thiolase are either missing or function improperly. 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.
Mitochondrial Trifunctional Protein deficiency is an autosomal recessive disease. Only when babies inherit two faulty copies of the gene for mitochondrial trifunctional protein 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 will be normal that they are called disease carriers. MTPD is inherited in autosomal recessive manner.
If both parents are MTPD 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 (whom is not affected), 50% (1 in 2) chance that the child has with one normal and one faulty gene whom is a carrier just like parents, and 25% (1 in 4) chance that the child has two copies of faulty gene that at risk for MTPD.
MTPD can be very variable in presentation causing milder symptoms in some babies and more serious problems in others. Severely affected babies develop symptoms in the neonatal to infancy period and present in metabolic crisis. Metabolic crisis is a period of time when a metabolic disorder makes the baby seriously ill.
Mildly affected/late-onset type babies may develop symptoms in childhood or adolescence.
Metabolic paediatricians and dieticians will work together to give expert advice and care to the babies with MTPD. 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 MTPD be fed regularly and do not go for long periods without eating.
Treatment for MTPD usually includes
It is 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 MTPD, 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)
March 2026
Hospital Authority