Conditions Argininosuccinic Aciduria

Argininosuccinic aciduria (ASA) is a condition that causes dangerous amounts of ammonia to build up in the body. ASA is considered an amino acid condition because people with ASA are unable to process a waste product, ammonia, that is produced when the body breaks down amino acids. You may also hear ASA described as a urea cycle condition. This name is used to describe conditions in which the body’s system for removing ammonia from the blood is not working correctly. Early detection and treatment can prevent many of the serious outcomes of ASA.

Condition Type

Amino Acid Disorders


Argininosuccinic aciduria affects one out of every 70,000 babies born in the United States.

Also known as

  • ASA
  • Argininosuccinate lyase deficiency
  • Arginosuccinic acid lysase deficiency
  • Argininosuccinic acidemia
  • Argininosuccinyl-CoA lyase deficiency
  • Arginosuccinase deficiency
  • ASAuria
  • ASL deficiency

Follow-Up Testing

Your baby’s doctor may ask you if your baby is showing any of the signs of ASA (see Early Signs below). If your baby has certain signs, your baby’s doctor may suggest starting immediate treatment.

If your baby’s newborn screening result for argininosuccinic aciduria (ASA) was out of the normal range, your baby’s doctor or the state screening program will contact you to arrange for your child to have additional testing. It is important to remember that an out-of-range screening result does not necessarily mean that your child has the condition. An out-of-range result may occur because the initial blood sample was too small or the test was performed too early. However, as a few babies do have the condition, it is very important that you go to your follow-up appointment for a confirmatory test. Because the harmful effects of untreated ASA can occur soon after birth, follow-up testing must be completed as soon as possible to determine whether or not your baby has the condition.

Follow-up testing will involve checking your baby’s urine and blood samples for harmful amounts of acids and toxins. Certain acids and toxins build up in the body when a child has an amino acid condition, so measuring the amounts of these substances in your baby’s body can help doctors determine if your baby has a condition. High levels of orotic acid in the urine and high levels of ammonia and arginine, an amino acid, in the blood may indicate that your baby has ASA. Sometimes follow-up testing may include testing a very small sample of skin.

About Argininosuccinic Aciduria

Early Signs

There are two main forms of arginosuccinic aciduria (ASA), which differ in the age of onset. The first and most common form is seen in newborns. The first signs of ASA usually begin in the first few days after birth.

The second form is less common and is seen in children. Sometimes signs of ASA might not become apparent until late infancy or early childhood. In these cases, the signs are usually less severe.

Signs of ASA in babies include:

  • Poor appetite
  • Sleeping longer or more often 
  • Tiredness
  • Irritability
  • Vomiting
  • Trouble breathing
  • Seizures (also called epilepsy)
  • Involuntary or uncontrolled body movements
  • Delayed growth

Many of these signs may occur when your baby eats foods that their body cannot break down. They can be triggered by long periods of time without eating, illnesses, and infections.

If your baby shows any of these signs, be sure to contact your baby’s doctor immediately.


Dietary Treatments

Your baby may need to follow a low-protein diet to avoid certain foods that he or she cannot break down. A dietician or nutritionist can help you plan the appropriate diet for your child’s healthy growth.

Your baby’s doctor might also recommend special formulas and foods for children with arginosuccinic aciduria (ASA). These formulas will likely need to continue through adulthood.

Supplements and Medications

Many babies with ASA take arginine supplements. Arginine is a natural substance, and it can help lower the high ammonia levels that result from ASA. Everyone has some ammonia in his or her blood, but high levels can be toxic. Your baby’s doctor can write you a prescription for these supplements.

Expected Outcomes

When arginosuccinic aciduria (ASA) is treated early, children can have healthy growth and development. This is why screening for ASA is so important. Newborn screening can allow for treatment before ammonia levels become dangerously high in your baby’s bloodstream.

Some children still have high ammonia levels in their blood even with treatment. These children may need to seek treatment in a hospital to remove the ammonia from their blood.

It is very important to treat ASA. Babies who do not receive treatment are at risk for intellectual disabilities, developmental delays, liver damage, brain damage, coma, or death.


When we eat food, enzymes help break it down. Some enzymes break down proteins into their building blocks, called amino acids. Other enzymes break down these amino acids further into their base molecules. When we break down proteins, our bodies need even more enzymes to get rid of waste products. In arginosuccinic aciduria, the enzyme arginosuccinic acid lyase (ASAL) is not working correctly.

ASAL’s job is to help get rid of ammonia by breaking it down into urine. Ammonia is a waste product of protein breakdown.

Babies with argininosuccinic aciduria (ASA) either do not make enough or make non-working ASAL. When ASAL does not work correctly, the body cannot remove ammonia through the urine. This causes a dangerous build-up of ammonia in the body.

ASA is an autosomal recessive genetic condition. This means that a child must inherit two copies of the non-working gene for ASA, one from each parent, in order to have the condition. The parents of a child with an autosomal recessive condition each carry one copy of the non-working gene, but they typically do not show signs and symptoms of the condition. While having a child with ASA is rare, when both parents are carriers, they can have more than one child with the condition. Learn more about autosomal recessive inheritance.

Support for Argininosuccinic Aciduria

Support Services

Support groups can help connect families who have a child or other family member affected with argininosuccinic aciduria with a supportive community of people who have experience and expertise in living with the condition. These organizations offer resources for families, affected individuals, health care providers, and advocates.

Accessing Care

Work with your baby’s health care provider to determine the next steps for your child’s care. Your baby’s doctor may help you coordinate care with a doctor who specializes in metabolism, a dietician who can help plan your child’s specialized diet, and other medical resources in your community. Depending on the signs and symptoms your baby experiences, your baby’s doctor may work with other doctors who specialize in treating the liver or brain. Some children with argininosuccinic aciduria (ASA) have developmental delays. If you think that your baby is not meeting his or her developmental milestones, ask your baby’s doctor about the next steps in accessing a developmental evaluation and care.

Because ASA is a genetic condition, you may want to talk with a genetics specialist. A genetic counselor or geneticist can help you understand the causes of the condition, discuss genetic testing for ASA, and understand what this diagnosis means for other family members and future pregnancies. Speak with your baby’s doctor about getting a referral. The Clinic Services Search Engineoffered by the American College of Medical Genetics and Genomics and the Find a Genetic Counselor tool on the National Society of Genetic Counselors (NSGC) website are two good resources for you or your baby's health care provider to use to identify local specialists.

Families' Experiences

Jonathan is a young boy with argininosuccinic aciduria (ASA). Jonathan did not have the benefit of having his condition diagnosed soon after birth and as a result of newborn screening, but rather his ASA was diagnosed at age 3. Read about Jonathan’s path to diagnosis and his improved health with treatment on the Save Babies Through Screening Foundation website.

References & Sources

Visit MedlinePlus Genetics for more condition information

Visit the Screening, Technology And Research in Genetics (STAR-G) Project for more information on ASA

ACT Sheets

Healthcare professionals can learn more about confirmatory testing by reading the American College of Medical Genetics and Genomics' Algorithm for Diagnosis and ACT Sheet, a guide for follow-up after newborn screening. You can visit this page of the ACMG website here.

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