Argininosuccinic aciduria (ASA) is an inherited disorder that is caused by the lack of an enzyme called argininosuccinate lyase. This deficiency results in difficulty breaking down nitrogen, which leads to a buildup of ammonia in the body. Ammonia is toxic to the body if it cannot be excreted and can affect the nervous system.
You may hear ASA called other names, like argininosuccinase deficiency, ASL deficiency, or argininosuccinic acid lyase deficiency.
Common symptoms of ASA include:
The symptoms developed due to ASA depend on how severe the disease is. If you or your child still have some argininosuccinate lyase enzyme, you may develop the disease later in life or develop less severe symptoms.
ASA is caused by changes in a specific gene called ASL. Genes can be thought of as an instruction manual for generating proteins that help the body to function properly.
When there’s a change, or mutation, in a gene, it can mess up the protein it’s supposed to make. This can cause problems in different parts of the body.
ASA is inherited in a specific way called autosomal recessive. Most traits and diseases are determined by the genes we get from our parents. With recessive disorders, you need to inherit two copies of the altered gene – one from each parent – to have the condition.
If you inherit only one altered gene and one normal gene, you’re what’s called a carrier. Carriers usually do not have symptoms themselves, but their children are at risk of receiving the altered gene.
When two carrier parents have a child, there’s a 25% chance the child will inherit both altered genes and have the condition. There’s also a 50% chance the child will be a carrier, and a 25% chance the child will inherit normal genes from both parents and not have the condition or be a carrier. This chance is the same for boys and girls.
The only risk factor for developing ASA is having a family history of ASA. Parents may want to consider genetic testing if they are trying to conceive.
Most newborns are examined for ASA and similar conditions. ASA is diagnosed using family medical history, a physical examination and blood tests to detect excess amounts of ammonia.
Genetic testing or a urine sample to detect for high amounts of argininosuccinic acid can confirm a diagnosis.
Complications of ASA include developmental delays, brain injury, and a coma. It’s important to receive swift treatment if your newborn, an older child or an adult is presenting with symptoms of ASA.
Treatment of ASA is dedicated to managing the blood levels of ammonia. Specialised diets combined with medications that can remove ammonia from the body work to keep people with ASA safe and healthy.
If you or your child has ASA, you will need to work with a team of specialists for the rest of your life to prevent high levels of blood ammonia and to manage high levels of blood ammonia (hyperammonaemic episodes).