Aromatic L-amino acid decarboxylase (AADC) deficiency is a genetic condition that affects the body’s nervous system.^1,2 It is caused by genetic changes (variants) in the dopa decarboxylase (DDC) gene, which is involved in production of neurotransmitters (signals that the body’s nerve cells use to talk to each other). In AADC deficiency, the neurotransmitters are not produced correctly, which affects communication between the nerve cells and prevents the nervous system from functioning properly.

Individuals with AADC deficiency may not show any symptoms at birth but may develop symptoms within the first few months of life.² There are a wide range of symptoms, with varying severity. Some of the more common symptoms include low muscle tone of the body torso (hypotonia), eyes stuck in an upward position (upward deviation of eyes) for a period of time, as well as uncontrollable movement of other body parts such as the head, face and neck.^1,2 Individuals also have trouble controlling their body temperature, blood pressure and heart rate.¹

Synonyms: Aromatic amino acid decarboxylase deficiency; AADC deficiency; DDC Deficiency; dopa decarboxylase deficiency.¹

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:35708 Aromatic L-amino acid decarboxylase deficiency

ICD-11: 5C59.00 Disorders of catecholamine synthesis

Symptoms of AADC deficiency may not be present at birth but may develop within the first few months of life.² Symptoms may include:^2,3

• low muscle tone (hypotonia)
• oculogyric crises – a movement disorder (dystonia) where eyes get locked in an upward position (upward deviation)and can’t be controlled for a period of time
• developmental delay
• feeding issues
• sleep disturbances
• seizures

There is also dysfunction of the autonomic nervous system, which may lead to issues with blood pressure, heart rate, regulation of body temperature and digestion.^1-3 There may also be other symptoms that have not been listed here.

Please speak to your medical team to learn more about the signs and symptoms of AADC deficiency.

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.

AADC deficiency is a genetic condition. It is caused by disease-causing genetic changes (variants) in the DDC gene. The DDC gene is responsible for making the AADC enzyme that is involved in the production of neurotransmitters.

All individuals have two copies (alleles) of the DDC gene – one on each chromosome that is inherited from each parent. AADC deficiency is an autosomal recessive condition, which means both copies of the DDC gene must have the disease-causing genetic variants.

Individuals with the genetic variant in only one copy are unaffected but will be a carrier and may pass on that variant to their children. If both parents are carriers (each have a copy of the disease-causing variant), there is a 25% chance the child will inherit both disease-causing variants and have AADC deficiency. 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

Diagnosis of AADC deficiency may be made based on a spinal tap and blood tests that show abnormal levels of neurotransmitters and enzymes related to the disorder. Genetic testing may be used to confirm the diagnosis. It is recommended that doctors use at least two of these methods to diagnose AADC deficiency.⁴

A urine metabolic screen can also be performed to look for increased levels of urine vanillactic acid (VLA), which can be indicative of AADC deficiency; however normal levels of VLA do not exclude an AADC deficiency diagnosis.⁴

Further information about diagnostic tests for AADC deficiency can be found in an international consensus guideline prepared by the International Working Group on Neurotransmitter Related Disorders (iNTD) and patient representatives – Consensus guideline for the diagnosis and treatment of aromatic l-amino acid decarboxylase (AADC) deficiency.⁴

A differential diagnosis can rule out other conditions that have similar symptoms, such as tetrahydrobiopterin (BH4) deficiency, sepiapterin reductase deficiency (SRD), succinic semialdehyde dehydrogenase (SSADH) deficiency, tyrosine hydroxylase deficiency and cerebral palsy.²

Please speak to your medical team to learn more about the available diagnostic pathways for AADC deficiency.

There is currently no curative treatment for AADC. Treatment of AADC can be complex and challenging, and involves a multidisciplinary care team.^2,3 The treatment regimen may consist of various medications that may help to alter the level of neurotransmitters and/or communication between neurons (nerve cells). There are also therapies for managing symptoms (symptomatic management), which may include medication to help with oculogyric crises and other motor symptoms, physiotherapy, speech therapy, feeding therapy, seizure management and others.^2,3

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.

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.

Healthcare professionals involved in the treatment of AADC deficiency may include general practitioners (GP), paediatricians, geneticists, metabolic physicians, neurologists, physiotherapists, speech therapists, dieticians and psychologists. The need for different healthcare professionals may change over a person’s lifetime and may extend beyond those listed here.

We are not aware of any clinical care guidelines for AADC deficiency in Australia. If you know of any relevant care guidelines, please let us know via the Contribute page.

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:

• Consensus guideline for the diagnosis and treatment of aromatic l-amino acid decarboxylase (AADC) deficiency is an international consensus guideline prepared by the International Working Group on Neurotransmitter Related Disorders (iNTD) and patient representatives; published in 2017. This guideline is intended for metabolic specialists, child and adult neurologists, pediatricians, intensive care specialists, nurses, and paramedical specialists involved in the care of patients with AADC.

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.

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.

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 any clinical trials with your medical team to determine suitability and eligibility.

Please note that RVA does not necessarily monitor or endorse each group/organisation’s operational governance and activities.

We are not aware of any rare disease organisations for AADC deficiency in Australia. If you are aware of any Australian organisations, please let us know via the Contribute page.

International Organisation:

The AADC Research Trust (United Kingdom)
Website: https://www.aadcresearch.org/

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.

AADC deficiency 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.

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, including families and carers, 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 people 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 on AADC deficiency can be found at: 

• Genetic and Rare Diseases (GARD) Information Center: Aromatic L-amino Acid Decarboxylase Deficiency
• National Organization for Rare Disorders (NORD): Aromatic L-Amino Acid Decarboxylase Deficiency 

• Online Mendelian Inheritance in Man, OMIM®: #608643 Aromatic L Amino Acid Decarboxylase Deficiency
• Orphanet: Aromatic L Amino Acid Decarboxylase Deficiency
• Human Phenotype Ontology (HPO): Aromatic L Amino Acid Decarboxylase Deficiency

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.