What is Argininosuccinic Aciduria?
Argininosuccinic aciduria (ASL deficiency) is a urea cycle disorder that results from deficiency of the enzyme, argininosuccinate lyase. Defects in this enzyme cause increased levels of argininosuccinic acid and citrulline (amino acids) in the body, because the body cannot convert them into arginine. As a result, ammonia may build up in the body instead of being removed through the urea cycle, which contributes to disease symptoms. There are two forms of the disease:
The neonatal-onset form is severe. It is noticed within the first few days of life by symptoms such as vomiting, lethargy, hypothermia, poor feeding, and tachypnea (rapid breathing). If left untreated, symptoms will progress and eventually lead to seizures, coma, and death. Other early symptoms may include brittle hair and an enlarged liver.
The late onset form can have a wide range of symptoms. Some symptoms include, but are not limited to, periodic increases in ammonia levels, developmental delay/intellectual disability, and behavioral abnormalities.
How common is Argininosuccinic Aciduria?
Argininosuccinic aciduria has an estimated incidence of 1 in 70,000, though this number may vary by region. For example, a founder effect has been described in Finland, Saudi Arabia, and the Druze community and thus, carrier risk and incidence of ASL deficiency may be higher in these areas.
How is Argininosuccinic Aciduria treated?
Argininosuccinic aciduria is primarily controlled by restricting protein from the diet and by taking arginine supplements. Other drugs called nitrogen-scavenging drugs may also help maintain lower amounts of ammonia in the body. In individuals where ammonia levels cannot be managed by the aforementioned therapies, or in those with liver cirrhosis, a liver transplant may be considered.
Acute hyperammonemic episodes are treated in a hospital. Though intravenous supplements and nitrogen-scavenging drugs can help lower the amount of ammonia in the body, hemodialysis may be necessary if these measures are ineffective.
What is the prognosis for a person with Argininosuccinic Aciduria?
There is no cure for argininosuccinic aciduria and the prognosis depends upon the severity of the symptoms. Individuals who have milder symptoms and who are provided with early dietary and therapeutic interventions will have a more favorable outcome, but they will still require long-term treatment to prevent additional neurologic and liver damage. Those who have more severe symptoms could experience seizures, coma, and early death. It is important to remember that treatments to reduce ammonia levels in the body do not prevent cognitive issues (for example, many individuals have mild to moderate intellectual disability), liver disease, brittle hair, and high blood pressure.