Argininosuccinic Aciduria

What else is it called?

  • Argininosuccinate lyase deficiency
  • Argininosuccinic acidemia
  • Argininosuccinicaciduria
  • Argininosuccinyl-CoA lyase deficiency
  • Arginosuccinase deficiency
  • ASA
  • ASAuria
  • ASL deficiency

Get in touch

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What causes it?

Argininosuccinic Aciduria is a rare inherited metabolic disorder. It is often shortened to ASA.

ASA affects the way your baby breaks down protein. Many foods contain protein. The body needs protein for growth and repair. Many people eat more protein than the body needs.

To remove excess protein from the body: First, the body converts waste protein to a toxic chemical called ammonia. Ammonia is then converted into a non-toxic chemical (urea) in the liver. This process occurs via the urea cycle. In the urea cycle, several steps have to take place. Each step needs an enzyme (like chemical scissors) for it to work. Urea is then removed by the kidneys.

In ASA, the body lacks an enzyme called argininosuccinate lyase. This means the liver cannot convert waste protein into urea as fast as normal. It can lead to high ammonia levels, particularly at times of increased protein breakdown.

Ammonia levels can rise when there is an increased break down of protein. This may happen if too much protein is eaten. It commonly results from break down of the body’s own protein. This is often triggered by infections, particularly if there is vomiting. This causes catabolism which is a breakdown of body protein and can lead to a metabolic crisis.

How common is it?

ASA occurs in approximately 1 in 70,000 newborns.

What are the signs and symptoms?

Some babies become ill in the first few days of life. Signs and symptoms include:

  • Poor feeding
  • Vomiting
  • Floppiness
  • Excessive sleepiness
  • Rapid breathing
  • Dehydration (lack of body fluids)
  • Seizures

The effects of high ammonia can quickly become life-threatening if untreated.

Some babies may present later.

There may be learning difficulties and delays to normal development, like walking and talking. It may also affect the liver or other parts of the body.

In ASA it is important that enough protein is given to grow… but not too much, as it will make waste protein causing high ammonia levels.

How is it diagnosed?

The diagnosis is suspected in a patient with high ammonia levels because of the pattern of chemicals in the blood and urine. The diagnosis is confirmed by finding the mutation in the ASA gene.

Can it be treated?

ASA is managed with the following:

  • A protein restricted diet
  • Sometimes a special amino acid supplement may be needed
  • Sufficient energy supply from food and feeds
  • Regular feeding
  • Arginine supplements
  • Vitamin and mineral supplements
  • Other medications to control the level of ammonia in the blood

Tube feeding may be necessary to give regular feeds. This will ensure energy, nutrient and fluid needs are met.

During any childhood illness, an emergency regimen is given. This will reduce the breakdown of protein and the build-up of ammonia. During illness:

  • Stop all protein in food & drink
  • Start the emergency regimen. This is made up of glucose polymer
  • Continue medication as prescribed

Always take full amounts of emergency feeds as prescribed. If symptoms continue and/or you are worried, go immediately to the hospital. Regularly update your metabolic team.

It is imperative that emergency feeds are started promptly and there are no delays in management.

If you have ASA you will need to be monitored frequently. This includes:

  • Frequent blood tests to check amino acids, nutrient and chemical levels
  • Height and weight
  • Developmental checks
  • Diet and medications are adjusted according to age, weight and blood chemical levels

Do my family need to be tested?

Humans have chromosomes composed of DNA. Genes are pieces of DNA that carry the genetic instruction. Each chromosome may have several thousand genes.

The word mutation means a change or error in the genetic instruction. We inherit particular chromosomes from the egg of the mother and sperm of the father.

The genes on those chromosomes carry the instruction that determines characteristics, which are a combination of the parents. ASA is an inherited condition. There is nothing that could have been done to prevent your baby from having ASA.

Everyone has a pair of genes that make the argininosuccinate lyase enzyme. In children with ASA, neither of these genes works correctly. These children inherit one non-working ASA gene from each parent.

Parents of children with ASA are carriers of the condition. Carriers do not have ASA because the other gene of this pair is working correctly.

When both parents are carriers, in each pregnancy the risk to the baby is as follows:

• 25% chance (1 in 4) of ASA

• 50% chance (1 in 2) for the baby to be a carrier of ASA

• 25% chance (1 in 4) for the baby to have two working genes and neither have ASA or be a carrier

Diagram showing the autosomal recessive inheritance pattern.

Relevant Organisations

This information is from the TEMPLE Guides which have been adapted by the Dietitians Group of the British Inherited Metabolic Disease Group (BIMDG) and is based on the original TEMPLE written by Burgard and Wendel. The TEMPLE Guides are supported by Nutricia. Dated February 2017.

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