Tricarboxylic acid cycle disorder

Tricarboxylic acid (TCA) cycle disorders, also known as citric acid cycle disorders or Krebs cycle disorders, are a group of rare inherited metabolic diseases caused by deficiency of one or more enzymes involved in the tricarboxylic acid cycle — the central metabolic pathway within mitochondria responsible for generating cellular energy. The TCA cycle is essential for the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins, and defects in this pathway lead to impaired energy production affecting multiple organ systems, particularly those with high energy demands such as the brain, skeletal muscle, and heart. This group encompasses several distinct enzyme deficiencies, including fumarase deficiency, alpha-ketoglutarate dehydrogenase deficiency, succinate dehydrogenase deficiency, aconitase deficiency, and others. Clinical features vary depending on the specific enzyme affected but commonly include neurological impairment (developmental delay, intellectual disability, seizures, encephalopathy), metabolic acidosis, lactic acidosis, hypotonia, and failure to thrive. Some forms present in the neonatal or infantile period with severe encephalopathy, while others may have a more variable age of onset. Characteristic organic acid abnormalities can often be detected in urine, aiding diagnosis. Treatment for TCA cycle disorders is largely supportive and symptomatic, as no curative therapies currently exist for most forms. Management may include dietary modifications, cofactor supplementation (such as thiamine or riboflavin depending on the specific defect), avoidance of metabolic stressors such as fasting or illness, and aggressive management of metabolic crises. Seizure management, physical therapy, and developmental support are important components of care. Prognosis varies widely depending on the specific enzyme deficiency and severity of the presentation, with some forms carrying a very poor prognosis while others may have a milder course.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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