Argininosuccinic aciduria (ASA) is a genetic, metabolic condition where there is a build-up of ammonia in the blood. Ammonia is produced when the body breaks down protein from food, and is toxic at high levels.¹ The body’s liver normally converts ammonia into urea (which is then excreted from the body in urine) through a metabolic process called the urea cycle.

Argininosuccinic aciduria (ASA) is a urea-cycle disorder, in which one of the urea cycle enzymes (argininosuccinate lyase or ASL) is not working properly and fails to convert argininosuccinic acid to arginine and fumarate.² This prevents ammonia from being completely converted to urea and results in build-up of argininosuccinic acid and ammonia. High levels of ammonia in the blood (hyperammonemia) can be toxic, particularly to the body’s nervous system. This can result in symptoms such as extreme tiredness and lack of energy (lethargy), vomiting, seizures and breathing difficulties in babies.^1-4 Hyperammonemia can also have long-term effects such as developmental delay, intellectual disability, liver issues, and other complications. If left untreated, episodes of severe hyperammonemia can lead to coma and early death. In some cases, symptoms of ASA may only present later on in childhood or in adulthood (late onset ASA).^2,3

In Australia, ASA is often detected shortly after birth via newborn bloodspot screening (NBS) programs. Additional testing is required to confirm a diagnosis. For individuals who are not screened at birth, ASA is often diagnosed after symptoms develop. Early detection and management of ASA is important to reduce or prevent the risk of life-threatening hyperammonemia.

Synonyms:^1-2 Argininosuccinase deficiency; Argininosuccinatelyase deficiency; Argininosuccinic acid lyase deficiency; Argininosuccinic acidemia; Arginosuccinase deficiency; ASA deficiency; ASL deficiency; Asl-gene related argininosuccinate lyase deficiency; Deficiency of argininosuccinate lyase

Universal rare disease classifications provide a common language for recording, reporting and monitoring diseases. Please visit the Rare Disease Classifications page for more information about these internationally recognised classifications.

ORPHA:23 Argininosuccinic aciduria

ICD-11: 5C50.A0 Argininosuccinic aciduria

Symptoms of ASA are caused by the build-up of ammonia in the blood.³ Symptoms can present shortly after birth (newborn/neonatal period), which is also known as the neonatal-onset ASA.^2,4  In some people, symptoms may only present later after the neonatal period – this can be later in childhood or in adulthood and is known as late-onset ASA. Late-onset ASA is often brought on (triggered) by stress, infections, stress or high protein intake.²

Babies with neonatal-onset ASA may display symptoms such as extreme tiredness and lack of energy (lethargy), vomiting, lack of appetite or refusal to feed and irritability.^1-4 They may also have an enlarged liver (hepatomegaly), abnormal breathing and seizures. If left untreated, the condition can worsen and lead to coma and early death. Episodes of hyperammonemia can also have long-term effects such as developmental delay, intellectual disability, hypertension, liver disease and other complications.

In the case of late-onset ASA, episodes of hyperammonemia tend to occur during periods of stress, illness, or after high protein intake.^2,4 Individuals with late onset ASA can have similar long-term complications of hyperammonemia as neonatal-onset ASA. There are some reported cases of individuals with learning disabilities even without any episodes of hyperammonemia. There are also some individuals which have no symptoms (asymptomatic).^2-3

Please speak to your medical team to learn more about the symptoms of this condition.

Rare diseases are often serious and progressive, exhibiting a high degree of symptom complexity, leading to significant disability. Majority of the estimated two million Australians living with a rare disease meet the Australian Government’s definition for disability (in accordance to the Australian Public Service Commission and Australian Bureau of Statistics), and many experience severe and permanent disability impacts. If you or someone you care for is experiencing disability-related impacts from a rare condition, please speak with a health or disability professional for advice. Information about relevant disability support can be found at the RARE Portal’s Disability Support Information page.

Orphanet: Disability – Argininosuccinic aciduria  has information about the  activity limitations that people with ASA may face; please note that this was last updated in 2019 and may not reflect the most current information.

Argininosuccinic aciduria (ASA) is a genetic condition. It is caused by disease-causing genetic changes (variants) in the ASL gene on chromosome 7. ² The ASL gene is responsible for producing an enzyme called argininosuccinate lyase.

All individuals have two copies (alleles) of the ASL gene – one copy inherited from each parent. ASA is an autosomal recessive condition, which means both copies of the ASL gene must have the disease-causing genetic variants.^2-4 More information on autosomal recessive inheritance pattern can be found at Centre for Genetics Education: Autosomal recessive inheritance.

If you would like to learn more about the inheritance and impact of this condition, please ask your doctor for a referral to a genetic counsellor. Genetic counsellors are qualified allied health professionals who can provide information and support regarding genetic conditions and testing. More information about genetic counselling can be found at:

• Information on Genetic Services
• The National and State Services pages underneath the ‘Genetic Counselling’ sections listed

Newborn screening

In Australia, ASA is usually detected via the newborn bloodspot screening (NBS) programs.  Shortly after birth and with parental consent, a nurse or midwife will collect the baby’s blood via a heel prick blood test. The healthcare provider will then send it to a specific laboratory to test for a range of rare conditions, including ASA. If the test results suggest that there is a risk of the baby having one of screened conditions, laboratory staff will promptly get in touch with healthcare providers. The healthcare providers will then arrange for the baby to have further testing to confirm if the baby actually has the condition. The healthcare providers will also organise for the baby to receive urgent care if required. Depending on your state or territory, parents may or may not receive a notification if the test results are clear. You can find out more about NBS in your state or territory at Australian Government Department of Health, Disability and Ageing: Delivering newborn bloodspot screening programs.

Newborn bloodspot screening is a reliable way to check for certain rare conditions early in life. Although it’s extremely rare, cases can sometimes be missed. If you are concerned your baby may have a condition that they have already been screened for, you should contact a medical professional.

Diagnosis

A diagnosis of ASA may be suspected based on an abnormal result from NBS but additional tests or a clinical examination will be required to confirm a diagnosis. For individuals who are not screened at birth, ASA is often diagnosed after symptoms develop.

Diagnosis of ASA may be made based on clinical evaluation of symptoms, laboratory tests on blood and urine samples to detect for increased levels of argininosuccinic acid, ammonia and citrulline, and confirmed by genetic testing.²

As part of the diagnostic process, doctors may do a differential diagnosis, which is to rule out other similar conditions, such as neonatal sepsis, other urea cycle disorders such as carbamoyl-phosphate synthetase 1 deficiency, ornithine transcarbamylase deficiency, citrullinemia type I and arginase deficiency, and other conditions that can cause hyperammonemia.^2,5

Please speak to your medical team to learn more about the available pathways for diagnosis of this condition.

There is currently no curative treatment for ASA. Early diagnosis and appropriate management can help prevent or reduce the risk of life-threatening hyperammonemia but may not always be able to prevent long-term complications.² Treatment focuses on prompt management of hyperammonemia,  prevention of episodes of hyperammonemia including through long-term dietary management, and management of any long-term complications.⁴

Hyperammonemia can be life-threatening and requires urgent medical treatment. Long-term dietary management involves a protein-restricted diet, alongside arginine supplementation.^2-6 The tolerated amount of protein in diets may vary between individuals and may change over time.⁶ It should be managed by a metabolic specialist team. In cases where a protein-restricted diet is not able to control the condition and there are repeated episodes of hyperammonemia, use of nitrogen scavenging medications may be considered.^2,4,5

Strategies to manage symptoms and complications may include management of seizures, management of the hypertension, physiotherapy, occupational therapy, and treatment of liver disease.⁴

Please speak to your medical team to learn more about the possible treatment or management options for your condition. Treatment will depend on an individual’s specific condition and symptoms. It is also important to stay connected to your medical team so that you can be made aware of any upcoming clinical trial opportunities. For many rare diseases, treatment options may be limited. Participation in a clinical trial may provide access to new or emerging therapies.

Healthcare professionals involved in the clinical care of individuals with ASA may include metabolic doctors such as physicians, dieticians, neurologists, hepatologists, as well as speech therapists, occupational therapists, physiotherapists, and other healthcare workers that are trained to look after metabolic conditions. The need for different healthcare professionals may change over a person’s lifetime and extend beyond those listed here.

Metabolic Dietary Disorders Association (MDDA): Metabolic Clinics include a list of metabolic clinics in Australia that provide comprehensive diagnostic and management services for children and adults with inborn errors of metabolism.

Clinical care for rare diseases often involves a multidisciplinary team of medical, care and support professionals. Please note that the information provided here is as a guide and that RVA does not necessarily monitor or endorse specific clinics or health experts.

This may not be applicable to all rare diseases but for many, palliative care services may be relevant and useful. Palliative care services are available for people (adults, children and their families) living with a life-limiting illness and is not only for end-of-life care. It can also help at any stage of illness from diagnosis onwards, and will look different for different people. Palliative care services provide assistance, support, resources and tools to help people manage their illness and the symptoms, ease pain, and improve comfort and quality of life. If this is relevant to you and you wish to find out more information about palliative care and how it can help you, please visit:

• Australian Institute of Health and Welfare: Palliative care Overview
• Australian Government Department of Health, Disability and Ageing: Palliative care
• Palliative Care Australia

The ASIEM Low Protein Handbook for Urea Cycle Disorders has been prepared by members of the Australasian Society for Inborn Errors of Metabolism (ASIEM), a special interest group of the Human Genetics Society of Australasia (HGSA), and was published in 2007.

The following guidance is available from international experts outside Australia; however, there may be information that is not relevant or applicable to the Australian context, and may not be up to date:

• Suggested guidelines for the diagnosis and management of urea cycle disorders: First revision, published in 2019, is an update of the 2012 guidelines involving a 17-expert panel assembled from eight different European countries and Israel.

Individuals living with rare diseases may have complex medical issues and disabilities, which are not always visible. It is often useful to refer to their medical history as well as personal information such as a medical card, doctor’s letter, or if available, a rare disease passport, for relevant information.

In addition, individuals, their parents, families and carers often develop extensive expertise on their specific rare disease. It is important to recognise that they can contribute valuable knowledge about their rare condition. Rare diseases often impact individuals differently, so it’s important to consider a person’s lived experience.

If you know of any relevant emergency management guidelines or information relevant to emergency care, please let us know via the  Contribute page.

Metabolic Dietary Disorders Association (MDDA): Latest Research Updates has information about key areas of ongoing research for various inborn errors of metabolism conditions, including urea cycle disorders.

There are specific considerations around participating in rare disease research, including clinical trials. It is important to be mindful of issues such as data privacy, research ethics, consent and differences in research regulations between Australia and other countries. For more information, please visit the RARE Portal’s Considerations for Participating in Health and Medical Research page.

If you are interested in finding clinical trials for your condition, please visit the following websites; however, there may not be any clinical trials available:

• Australian Clinical Trials
• ClinicalTrials.gov

It is best to discuss your interest in research, including clinical trials,  with your medical team to determine suitability and eligibility.

Australian Organisation:

Metabolic Dietary Disorders Association (MDDA)
Website: https://mdda.org.au/

Metabolic Dietary Disorders Association Inc (MDDA) is the national peak consumer body dedicated to supporting, educating, connecting, and representing all individuals their families and carers living with Inborn Errors of protein Metabolism (IEpM).

Please note that RVA does not monitor or endorse each group/organisation’s operational governance and activities. When engaging with a group, please consider the information on the RARE Portal’s Finding Helpful Peer and Community Supports page.

ASA varies between individuals, and each person’s experience is unique.

If you would like to share your personal story with RVA, please visit the Rare Voices Australia: Share Your Story page. RVA will consider your story for publishing on our website and inclusion on the RARE Portal.

• The ASIEM Low Protein Handbook for Urea Cycle Disorders
• Fruit and Vegetables Counting Lists
• Protein Counting List

For information on available government and social services that provide support for individuals with a rare disease, please visit the National and State Services pages.

People living with a rare disease often face unique challenges such as diagnostic delays, misdiagnoses, limited treatment options, and limited access to rare disease specialists and support. These challenges may impact people’s emotional wellbeing and quality of life. Many find it helpful to seek mental health and wellbeing support to cope with ongoing stress and uncertainty. Connecting with people who have shared experiences through a support group may also be helpful. Information about relevant mental health and wellbeing support can be found at:

• Mental Health and Wellbeing Support for Australians Living with a Rare Disease
• The National and State Services pages underneath the ‘Mental Health’ sections listed

Further information relevant to ASA can be found at:

• Metabolic Dietary Disorders Association (MDDA): Argininosuccinic Aciduria (ASA)
• Genetic and Rare Diseases (GARD) Information Center: Argininosuccinic aciduria
• National Organization for Rare Disorders: Argininosuccinic Aciduria
• The ASIEM Low Protein Handbook for Urea Cycle Disorder

Orphanet: Argininosuccinic aciduria

GeneReviews^®: Argininosuccinate Lyase Deficiency

Online Mendelian Inheritance in Man, OMIM^®: #207900 – Argininosuccinic aciduria

This page has been developed by Rare Voices Australia (RVA)’s RARE Portal team.

If you are aware of any additional information that may benefit stakeholders with an interest in this page, or if you notice any broken links or inaccurate information, please let us know via the Contribute page.