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Mitochondrial trifunctional protein deficiency
This condition can lead to serious health problems, particularly affecting the heart, muscles, and liver. It is caused by changes in genes involved in fatty acid oxidation, typically presenting in infancy or early childhood.
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Overview
Mitochondrial trifunctional protein (TFP) deficiency is a rare inherited metabolic disorder. It occurs when the body cannot properly process certain types of long-chain fatty acids, which are important sources of energy, especially during fasting or illness [PMID:31747833]. This inability to convert fats into energy can lead to a build-up of harmful substances and energy shortages in various parts of the body. The condition can manifest with a range of symptoms, from mild to severe, often presenting in infancy or early childhood. While rare, understanding TFP deficiency is important for early diagnosis and management.
Symptoms & clinical features
The symptoms of mitochondrial trifunctional protein deficiency can vary widely among affected individuals, ranging in severity. In infants, common signs may include feeding difficulties, vomiting, muscle weakness (hypotonia), and poor growth. Some children may experience episodes of hypoglycaemia (low blood sugar), which can be life-threatening if not treated promptly [PMID:31747833].
Other potential symptoms include cardiomyopathy (heart muscle disease), liver problems (hepatomegaly, or enlarged liver), and nerve damage (neuropathy), which can cause tingling, numbness, or weakness, particularly in the legs and arms. In some cases, individuals may experience rhabdomyolysis, a breakdown of muscle tissue that releases harmful proteins into the blood. Symptoms often worsen during periods of illness, fasting, or increased energy demand.
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Affected organs
Mitochondrial trifunctional protein deficiency primarily affects organs that rely heavily on fatty acid oxidation for energy. These include the heart, where impaired energy production can lead to cardiomyopathy, and the skeletal muscles, causing weakness, pain, or rhabdomyolysis. The liver is also commonly affected, leading to issues such as hepatomegaly and impaired glucose production, contributing to hypoglycaemia [PMID:20301726]. The nervous system can also be impacted, potentially leading to peripheral neuropathy, which affects the nerves outside of the brain and spinal cord.
Risks & severity
The severity of mitochondrial trifunctional protein deficiency can vary considerably. Some individuals experience severe symptoms from infancy, while others may have a milder presentation that emerges later in childhood or even adulthood. The most severe forms can be life-threatening if not managed appropriately, particularly during metabolic crises triggered by fasting or illness. Complications can include acute liver failure, severe cardiomyopathy, and irreversible neurological damage. While the exact prevalence is not well established, it is considered a rare condition.
Genetic causes
Mitochondrial trifunctional protein deficiency is caused by pathogenic changes in genes that are essential for the function of the mitochondrial trifunctional protein complex. One such gene is HADHB. The HADHB gene provides instructions for making the beta subunit of this complex. The mitochondrial trifunctional protein complex is located in the mitochondria, which are the 'powerhouses' of cells, and plays a crucial role in breaking down long-chain fatty acids to produce energy, a process known as fatty acid oxidation [PMID:31747833].
When there are pathogenic changes in HADHB, the beta subunit may be faulty or absent. This impairs the overall function of the mitochondrial trifunctional protein complex, leading to an inefficient breakdown of long-chain fatty acids. As a result, the body struggles to generate energy from these fats, and partially processed fatty acid by-products can accumulate to toxic levels. This disruption in energy metabolism and accumulation of harmful substances contribute to the varied symptoms observed in affected individuals.
- HADHB hydroxyacyl-CoA dehydrogenase trifunctional multienzyme complex subunit betaThe HADHB gene provides instructions for creating a vital component of the mitochondrial trifunctional protein, which is essential for processing long-chain fatty acids into energy.
Inheritance pattern
Mitochondrial trifunctional protein deficiency typically follows an autosomal recessive inheritance pattern. This means that an individual must inherit two copies of a pathogenic gene variant - one from each parent - to develop the condition.
Parents who each carry one copy of the pathogenic variant (carriers) usually do not show symptoms themselves because their other unaffected copy of the gene can compensate. When two carriers have children, there is a 25% chance with each pregnancy that the child will inherit two copies of the pathogenic variant and develop the condition, a 50% chance that the child will be a carrier like their parents, and a 25% chance that the child will inherit two unaffected gene copies and neither have the condition nor be a carrier.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
Diagnosis & testing
Diagnosis of mitochondrial trifunctional protein deficiency often begins with a clinical suspicion based on a child's symptoms, especially during metabolic crises. Initial investigations may include blood and urine tests to look for markers of fatty acid oxidation disorders, such as abnormal acylcarnitine profiles or organic acids.
Confirmation of the diagnosis typically involves genetic testing, which can identify pathogenic variants in genes like HADHB [PMID:31747833]. Genetic testing is available through the NHS Genomic Medicine Service (GMS) and is generally requested by a clinical geneticist or a metabolic specialist. The relevant NHS Genomic Medicine Service 'R-code' for testing for fatty acid oxidation disorders would be discussed with a specialist. Referral to a regional clinical genetics service or a metabolic centre is usually the pathway for obtaining a confirmed diagnosis.
Management & lifestyle
Management of mitochondrial trifunctional protein deficiency focuses on preventing metabolic crises and mitigating symptoms. This typically involves a specialised dietary plan, often supervised by a metabolic dietitian, to ensure adequate energy intake and avoid prolonged fasting. The diet may include regular meals and snacks, and sometimes supplementation with medium-chain triglycerides, which are easier for the body to process.
Patients are generally advised to avoid situations that could trigger a crisis, such as intense exercise or certain medications, and to have an 'emergency plan' for when they are unwell. Regular monitoring of heart function, liver function, and neurological status is important. Care is coordinated through specialist metabolic centres within the NHS, often involving a multidisciplinary team including metabolic paediatricians or physicians, dietitians, genetic counsellors, and other specialists as needed.
UK care pathway
In the UK, individuals suspected of having mitochondrial trifunctional protein deficiency would typically be referred to a specialist metabolic centre. The diagnostic process often involves clinical geneticists and specialist biochemical tests, leading to genetic testing via the NHS Genomic Medicine Service. Genetic counsellors play a vital role in explaining the condition, inheritance patterns, and implications for families. The specific R-code for genetic testing would be determined by the referring clinician based on the suspected gene.
Frequently asked questions
What does 'mitochondrial trifunctional protein' mean?
The mitochondrial trifunctional protein is a complex of three enzymes located inside the mitochondria, the energy-producing parts of our cells. It works like a team to break down long-chain fatty acids into energy for the body, particularly when glucose (sugar) is not readily available.
Is there a cure for mitochondrial trifunctional protein deficiency?
Currently, there is no cure for mitochondrial trifunctional protein deficiency. However, the condition is manageable through strict dietary control, avoiding fasting, and other supportive treatments. Early diagnosis and consistent management can significantly improve outcomes and reduce the severity of symptoms.
Can carriers of HADHB gene variants have symptoms?
Individuals who are carriers for a pathogenic HADHB variant typically do not experience symptoms of mitochondrial trifunctional protein deficiency. They have one working copy of the gene, which is usually enough to prevent the condition from developing. Carrier testing can be important for family planning.
What lifestyle changes are important for someone with this condition?
Key lifestyle changes include adhering to a strict, specialist-designed diet to ensure adequate calorie intake and avoid long periods without food (fasting). During illness, it's crucial to follow an 'emergency regimen' to prevent metabolic crises. Regular communication with a metabolic team is vital for ongoing guidance and support.
How is this condition diagnosed in newborns?
In some regions, fatty acid oxidation disorders, including TFP deficiency, may be part of newborn screening programmes, which involve a heel prick blood test shortly after birth. If the condition is suspected from screening or symptoms, further diagnostic tests like blood acylcarnitine analysis and genetic testing are performed to confirm the diagnosis.
References
- Vieira Neto E, Wang M, Szuminsky AJ. Mitochondrial bioenergetics and cardiolipin remodeling abnormalities in mitochondrial trifunctional protein deficiency. JCI insight. 2024. PMID: 39088276
- Schwantje M, Ebberink MS, Doolaard M. Thermo-sensitive mitochondrial trifunctional protein deficiency presenting with episodic myopathy. Journal of inherited metabolic disease. 2022. PMID: 35403730
- Daley SF, Shah M. Newborn Screening. 2026. PMID: 32644409
- Winter S, Buist NR, Longo N. Round Table Discussion. Annals of nutrition & metabolism. 2016. PMID: 27931031
- Qaiser F, McHugh J, Mullins G. Mitochondrial Trifunctional Protein Deficiency due to HADHA Variants Masquerading as Charcot-Marie-Tooth Disease. Journal of the peripheral nervous system : JPNS. 2025. PMID: 40790338
- Miklas JW, Ruohola-Baker H. Using Mitochondrial Trifunctional Protein Deficiency to Understand Maternal Health. Journal of cellular signaling. 2020. PMID: 32995760
- Bursle C, Weintraub R, Ward C. Mitochondrial Trifunctional Protein Deficiency: Severe Cardiomyopathy and Cardiac Transplantation. JIMD reports. 2018. PMID: 29124685
- Vieira Neto E, Wang M, Szuminsky AJ. Elamipretide Improves Mitochondrial Function in Mitochondrial Trifunctional Protein-Deficient Mice and Human Fibroblasts. Journal of inherited metabolic disease. 2026. PMID: 41500837