Overview
Hyperammonemic encephalopathy due to carbonic anhydrase VA deficiency (also called CA-VA deficiency) is an extremely rare inherited metabolic disorder. It is caused by mutations in the CA5A gene, which provides instructions for making an enzyme called carbonic anhydrase VA. This enzyme plays an important role inside the mitochondria (the energy-producing parts of cells), where it helps produce bicarbonate. Bicarbonate is needed for several critical metabolic pathways, including the urea cycle (which removes toxic ammonia from the body) and other processes involved in making glucose and fatty acids. When carbonic anhydrase VA is not working properly, ammonia builds up in the blood — a condition called hyperammonemia. High ammonia levels are toxic to the brain and can cause a condition known as encephalopathy, which involves confusion, lethargy, poor feeding, vomiting, and in severe cases, seizures and coma. Symptoms typically appear in the newborn period or early infancy, often triggered by illness or metabolic stress. Some patients also show low blood sugar (hypoglycemia) and abnormal levels of certain acids in the blood (metabolic acidosis or lactic acidosis). Treatment focuses on lowering ammonia levels quickly during acute episodes and preventing future crises. This may include medications that help remove ammonia (such as sodium benzoate or sodium phenylbutyrate), supplementation with N-carbamylglutamate (carglumic acid), and careful dietary management. With early diagnosis and proper management, outcomes can be improved, though long-term follow-up is essential. Because this disease is so rare, knowledge about its full spectrum and long-term prognosis is still growing.
Also known as:
Key symptoms:
High ammonia levels in the bloodLethargy or excessive sleepinessPoor feeding in infancyVomitingSeizuresLow blood sugar (hypoglycemia)Rapid breathingLow muscle tone (floppiness)IrritabilityConfusion or altered consciousnessMetabolic acidosis (too much acid in the blood)Elevated lactic acid levelsDevelopmental delays if untreatedComa in severe episodes
Autosomal recessive
Passed on when both parents carry the same gene change; often skips generations
Neonatal
Begins at or shortly after birth (first 4 weeks)
Treatments
No FDA-approved treatments are currently listed for Hyperammonemic encephalopathy due to carbonic anhydrase VA deficiency.
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Specialists
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Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
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Caregiver Resources
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Questions for your doctor
Bring these to your next appointment
- Q1.What is my child's current ammonia level, and what is the target range we should aim for?,Should my child take carglumic acid (Carbaglu), and if so, what is the right dose?,What is the sick-day emergency plan, and when should we go to the emergency room?,Does my child need a special diet, and should we see a metabolic dietitian?,How often should blood tests and metabolic monitoring be done?,What developmental milestones should we watch for, and does my child need early intervention services?,Are there other family members who should be tested for this condition?
Common questions about Hyperammonemic encephalopathy due to carbonic anhydrase VA deficiency
What is Hyperammonemic encephalopathy due to carbonic anhydrase VA deficiency?
Hyperammonemic encephalopathy due to carbonic anhydrase VA deficiency (also called CA-VA deficiency) is an extremely rare inherited metabolic disorder. It is caused by mutations in the CA5A gene, which provides instructions for making an enzyme called carbonic anhydrase VA. This enzyme plays an important role inside the mitochondria (the energy-producing parts of cells), where it helps produce bicarbonate. Bicarbonate is needed for several critical metabolic pathways, including the urea cycle (which removes toxic ammonia from the body) and other processes involved in making glucose and fatty a
How is Hyperammonemic encephalopathy due to carbonic anhydrase VA deficiency inherited?
Hyperammonemic encephalopathy due to carbonic anhydrase VA deficiency follows a autosomal recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does Hyperammonemic encephalopathy due to carbonic anhydrase VA deficiency typically begin?
Typical onset of Hyperammonemic encephalopathy due to carbonic anhydrase VA deficiency is neonatal. Age of onset can vary across affected individuals.