Argininosuccinate Lyase Deficiency

Gene : ASL

What is Argininosuccinate Lyase Deficiency?

Argininosuccinate lyase (ASL) deficiency, also known as Arginosuccinic aciduria, is an inherited disorder caused by accumulation of ammonia in the blood, due to a deficiency of the enzyme argininosuccinate lyase. Normally the body changes ammonia into urea which can be removed in the urine. People with ASL deficiency can't efficiently convert ammonia into urea, and ammonia will subsequently build up in their body. Highly elevated ammonia level is toxic to the body and may cause damage to the brain. If not treated promptly, babies with ASL deficiency normally show symptoms shortly after birth which may include lack of energy, poor appetite, breathing problems, lack of control of body temperature, seizures and coma. Other effects include developmental delay, intellectual disability, liver damage, skin lesions and brittle hair. Without treatment, affected babies may die within the first few weeks of life. There is no cure for ASL deficiency, though strict dietary management and liver transplantation have shown to have some effect on reversing or correcting some symptoms. ASL deficiency is caused by pathogenic variants in the ASL gene.

How is ASL deficiency inherited?

ASL deficiency is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

What does it mean to be a carrier?

There are generally no signs or symptoms associated with being a carrier for ASL deficiency. However, the risk to have a child affected with ASL deficiency is increased. Testing of reproductive partners is recommended for carriers of ASL deficiency.

How common is ASL deficiency?

ASL deficiency is estimated to occur in 1 in 70,000 newborns.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems




Carrier Rates
Detection Rate
Carrier Frequency
Finnish 90% 1 in 190
General Population 90% 1 in 133

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