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Carbonic anhydrase VA deficiency
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Carbonic anhydrase VA deficiency

Carbonic anhydrase VA deficiency is an inherited metabolic disorder that causes life-threatening episodes of brain dysfunction and chemical imbalances in the blood.

Overview

This disorder is characterized by episodes of metabolic crisis and acute encephalopathy. These episodes typically begin by age 2 and can be triggered by fasting or increased energy demands, such as illness. Between episodes, affected children are generally healthy, and the risk of crisis is thought to decrease after childhood.

Symptoms

During a metabolic crisis, individuals may experience:

  • Poor feeding, vomiting, and weight loss.
  • Lethargy and rapid breathing (tachypnea).
  • Seizures or coma.
  • Hyperammonemia: Excess ammonia in the blood.
  • Metabolic acidosis and respiratory alkalosis.
  • Hypoglycemia: Low blood glucose.

Causes

The condition is caused by mutations in the CA5A gene, which provides instructions for the carbonic anhydrase VA enzyme. This enzyme is vital in the liver for producing bicarbonate, which maintains the body's acid-base balance and supports mitochondrial enzymes. Impaired enzyme function leads to reduced bicarbonate, causing the biochemical imbalances that trigger metabolic crises.

Inheritance

Carbonic anhydrase VA deficiency is inherited in an autosomal recessive pattern, meaning both copies of the gene in each cell must have mutations. Parents of an affected individual typically carry one mutated copy but do not show symptoms. The condition exhibits reduced penetrance, meaning some individuals with two mutated copies may never develop symptoms.

Frequently Asked Questions

Yes. A high‑carbohydrate, low‑protein diet reduces ammonia production; supplementing with oral sodium bicarbonate supports the missing enzyme activity. During illness, give frequent carbohydrate‑rich fluids (e.g., dextrose‑containing oral rehydration solution) and avoid prolonged fasting. Some clinicians also prescribe chronic nitrogen‑scavenger therapy for children with frequent episodes.
Reduced penetrance means that two pathogenic CA5A copies may not always cause symptoms. Genetic testing can confirm carrier status in parents and siblings. Couples can consider pre‑implantation genetic diagnosis or prenatal testing, but they should discuss the uncertainty of disease expression with a genetic counselor.
Look for sudden poor feeding, vomiting, rapid breathing (tachypnea), lethargy, or a change in mental status. Even a mild drop in blood glucose or a new seizure‑like movement can be the first clue. Prompt measurement of blood ammonia and a basic metabolic panel is essential.
The team should start nitrogen‑scavenging drugs (e.g., sodium phenylbutyrate or sodium benzoate) to lower ammonia, provide intravenous glucose to prevent catabolism, and correct acid‑base disturbances with bicarbonate if needed. Hemodialysis may be considered for severe ammonia levels (>200 µmol/L) or if medical therapy fails.
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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