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Exploring hyperammonemia: How does this dangerous metabolic disorder occur?
Hyperammonemia, or elevated blood ammonia concentration, is a metabolic disorder characterized by excess ammonia in the blood. Severe hyperammonemia is a dangerous condition that can cause brain damage and death. This condition can be divided into primary and secondary. Ammonia is a nitrogenous substance that is typically a product of protein metabolism and is converted into the less toxic urea before being excreted in the urine. The metabolic pathway of urea involves a series of reactions that are first carried out in the mitochondria and then transferred into the cytoplasm. This process is called the urea cycle and involves a chain reaction of multiple enzymes.
Hyperammonemia is generally defined as blood ammonia concentration higher than 50 μmol/L in adults and higher than 100 μmol/L in newborns.
The impact and harm of hyperammonemia
When blood ammonia concentration exceeds 200 μmol/L, severe symptoms may occur, including seizures, encephalopathy, coma and even death. In addition, blood ammonia concentrations above 400 to 500 μmol/L are associated with a 5 to 10 times greater risk of irreversible brain damage.
Hyperammonemia is one of the metabolic disorders leading to hepatic encephalopathy, which causes astrocyte swelling and stimulates NMDA receptors in the brain.
Causes of hyperammonemia
The causes of hyperammonemia can be divided into primary and secondary. Primary hyperammonemia results from multiple inborn errors of metabolism characterized by reduced activity of any enzyme in the urea cycle. The most common example is ornithine aminotransferase deficiency, an X-chromosome genetic disorder.
Secondary hyperammonemia is caused by innate errors in intermediary metabolism. These errors are characterized by reduced activity of non-urea cycle enzymes or cellular dysfunction that contributes significantly to metabolism. For example, both acute liver failure and cirrhosis with liver failure may cause secondary hyperammonemia.
Diagnosis and types of hyperammonemia
Hyperammonemia can be divided into acquired and congenital forms. Acquired hyperammonemia usually results from acute liver failure, cirrhosis, or the effects of hepatotoxins. Chronic hepatitis C, chronic hepatitis B and excessive alcohol consumption are common causes of cirrhosis.
In clinical practice, doctors will determine the type and cause of hyperammonemia based on clinical manifestations, blood ammonia testing and related metabolic tests.
Treatment of hyperammonemia
The main goal of treating hyperammonemia is to limit ammonia uptake and promote its excretion. Common treatment options include limiting dietary protein intake and providing calories through glucose and fat.
Intestinal acidification therapy using lactulose can reduce blood ammonia concentration by protonating ammonia, which is a treatment method for hepatic encephalopathy.
For patients with primary urea cycle defects, intravenous arginine, sodium aminobenzoate, and aminophenylacetic acid can be used as adjuvant therapy. These drugs act as nitrogen excretion substitutes.
Summary
Hyperammonemia is a dangerous metabolic disorder that may be caused by a variety of factors, including congenital enzyme defects and acquired liver dysfunction. Understanding its causes and timely treatment are crucial to reducing the risks it poses. When facing this disease, we can't help but think: How to diagnose and treat hyperammonemia more effectively clinically to ensure the safety of patients' lives?
