Aromatic L-Amino Acid Decarboxylase Deficiency (AADC Deficiency)

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare genetic disorder that affects the brain’s ability to produce AADC, an enzyme needed to make neurotransmitters, which are chemical messengers that help control mood, movement, and other essential functions. AADC deficiency can lead to a range of challenges, particularly in children, including difficulty with motor control, communication, and behavior.

Symptoms of AADC deficiency usually begin within the first few months of life and can include:

• Developmental delays
• Feeding difficulties due to challenges with swallowing (dysphagia), muscle control, and coordination, increasing the risk of choking and feeding aversions
• Seizures
• Movement disorders including involuntary upward eye movements called “oculogyric crises”
• Low muscle tone and muscle weakness (hypotonia)

As children with AADC deficiency grow, they may develop other symptoms, such as speech delays, difficulty walking, and sleep disorders.

Diagnosing and treating AADC deficiency early can help manage a child’s symptoms and improve their quality of life.

AADC deficiency is caused by changes in the aromatic amino acid decarboxylase gene, which results in a malfunctioning AADC enzyme. This enzyme is essential for producing dopamine and serotonin, neurotransmitters that help control movement, mood, sleep, and other important functions. These processes get disrupted when a child can’t produce enough dopamine and serotonin due to a lack of the AADC enzyme.

AADC deficiency is an inherited condition that occurs when a child gets two copies of the faulty gene—one from each parent. People who carry one copy of the gene typically don’t show symptoms but can pass it on. If both parents are carriers, each of their children has a 25 percent chance of being affected and a 50 percent chance of being a carrier. The risk is the same for both boys and girls.

At Boston Children’s Hospital, we use several methods to diagnose AADC deficiency, including:

• A review of your child’s medical history
• A physical exam
• Genetic testing using a blood test
• Brain imaging
• Lumbar puncture (A procedure that collects a small amount of fluid from the spine to help identify certain conditions)

At Boston Children’s, we take a comprehensive approach to care, involving a range of services to support your child’s needs, including:

• Feeding and swallowing services
• Occupational therapy
• Physical therapy
• Respiratory support
• Speech therapy and augmentative communication
• Supportive care for managing infections and complications as well as caregiver and family support.

Additionally, gene therapy is a targeted treatment for AADC deficiency, approved by the FDA in November 2024 following a clinical trial at Boston Children’s. We are happy to be a qualified treatment center (QTC) for this therapy.

We are the first hospital in the country to offer a pioneering FDA-approved gene therapy for AADC deficiency. KEBILIDI™ is the first treatment in the U.S. to be administered directly to the brain through a minimally invasive procedure. The therapy helps restore dopamine production by delivering a functional DDC gene, improving both motor function and developmental progress.

The long-term outlook for children with AADC deficiency can vary depending on the severity of the condition, the child’s age at diagnosis, and their response to treatment. Without treatment, AADC deficiency is a progressive, life-shortening disorder that can lead to severe disability. However, with early diagnosis and treatment—particularly with gene therapy—the outlook has improved for some children. While gene therapy has shown positive results in clinical trials, the long-term benefits are still being evaluated.

Surgeries can address complications such as severe feeding difficulties or respiratory issues; these types of procedures include:

• G-tube placement: A gastrostomy tube can help with feeding when a child has difficulty swallowing or maintaining proper nutrition.
• Tracheostomy: A procedure that creates a small hole in the front of the neck to allow air to enter the lungs directly through a tube, helping improve breathing.
• Deep brain stimulation (DBS): In some cases, implanting a device that delivers electrical impulses to specific areas of the brain may help manage movement disorders associated with AADC deficiency.

At Boston Children’s, surgery is considered part of a comprehensive treatment plan that includes physical, speech, and occupational therapy services to manage symptoms and improve the overall quality of life for children with AADC deficiency.