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HADHB gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

HADHB gene

The HADHB gene provides instructions for creating the beta subunit of the mitochondrial trifunctional protein, which is essential for fatty acid metabolism.

Overview

The HADHB gene provides instructions for making the beta subunit of the mitochondrial trifunctional protein. This enzyme complex, located in the mitochondria, consists of eight subunits: four alpha subunits (from the HADHA gene) and four beta subunits (from the HADHB gene). The beta subunits contain the enzyme long-chain 3-keto-acyl-CoA thiolase.

This protein complex is required for fatty acid oxidation, the process of breaking down long-chain fatty acids into energy. This energy is vital for the heart, muscles, and liver, particularly during periods of fasting.

Health Conditions Related to Genetic Changes

Mitochondrial trifunctional protein deficiency

Mutations in the HADHB gene can cause mitochondrial trifunctional protein deficiency. These mutations reduce all three enzyme activities of the complex, leading to:

  • Structural alterations in the beta subunit.
  • Inability to convert long-chain fatty acids into energy.
  • Symptoms such as lethargy and hypoglycemia.
  • Damage to the liver, heart, and muscles caused by the buildup of partially metabolized fatty acids.

Other disorders

Some HADHB mutations specifically decrease only the long-chain 3-keto-acyl-CoA thiolase enzyme activity. This isolated deficiency presents with symptoms similar to the broader protein deficiency, including:

  • Feeding difficulties, lethargy, and hypotonia (weak muscle tone).
  • Liver problems and hypoglycemia.
  • High risk for serious heart complications, breathing difficulties, and sudden death.

Additionally, HADHB mutations are associated with an increased risk of acute fatty liver of pregnancy (AFLP) and HELLP syndrome in mothers carrying a fetus with mutations in both copies of the HADHB gene.

Frequently Asked Questions

Newborns may present with poor feeding, lethargy, low blood sugar, and muscle weakness. Cardiac arrhythmias or a heart murmur may be detected on an ECG or echocardiogram, and liver enlargement or abnormal liver enzymes can also be present.
Frequent, balanced meals with adequate carbohydrates and moderate protein help maintain glucose levels. Avoid prolonged fasting, especially during illness. In some cases, a medical nutritionist may recommend a specialized diet or the use of medium‑chain triglyceride supplements to provide an alternative energy source.
Patients with HADHB mutations are at risk for arrhythmias, cardiomyopathy, and sudden cardiac death. Regular cardiac evaluation—including ECG, Holter monitoring, and echocardiography—should be performed at least annually, or more frequently if symptoms arise. Early detection of rhythm abnormalities allows timely intervention.
Pregnancy can increase the risk of acute fatty liver of pregnancy (AFLP) and HELLP syndrome in mothers carrying a fetus with biallelic HADHB mutations. Maternal monitoring should include liver function tests, coagulation panels, and regular obstetric ultrasounds. Early detection of liver dysfunction can guide timely delivery and treatment.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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