The Role of Dopamine and AADC
in Parkinson’s Disease

Parkinson’s disease is characterized by a loss of dopamine and its function. Dopamine is a chemical “messenger” that is produced in the brain and is involved in the control of movement. Some chemicals, like dopamine, are made from other chemicals by proteins called enzymes. Dopamine is made in the brain when the enzyme AADC (Aromatic l-amino acid decarboxylase) converts the chemical levodopa to dopamine. Levodopa, AADC, and dopamine are each present at normal levels in healthy people.

When dopamine levels decrease in the brain and there is no longer enough to control movement, the motor symptoms of Parkinson’s disease may occur. When this happens, a doctor may prescribe a levodopa medication, which is converted into dopamine by the enzyme AADC in the same way that naturally occurring levodopa is converted to dopamine.

As Parkinson’s disease worsens, there is less AADC enzyme in parts of the brain where it is needed to convert levodopa to dopamine. Therefore, the amount of dopamine that is produced from each dose of levodopa medicine that you take is reduced. When this happens, your motor function may get worse and you may have a less predictable response to your medications.

That is why researchers have focused on developing an AADC gene therapy that may improve your brain’s ability to make dopamine and your motor function.

Experimental Gene Therapy for Parkinson’s Disease

The main purpose of this clinical study is to evaluate the safety and efficacy (if it works) of an experimental gene therapy on Parkinson’s disease motor function. A surgical procedure will be used to administer the experimental gene therapy, which involves placing the AADC gene into a specific part of the brain where it is needed to convert levodopa into dopamine. This is intended to program cells in the brain to produce the AADC enzyme needed and may improve motor function.*

*This gene therapy is currently being investigated and has not been approved for Parkinson’s disease.

How the Experimental Gene Therapy is Proposed to Work

This experimental gene therapy is designed to put the AADC enzyme into brain cells where it can convert levodopa to dopamine. To do this, the AADC gene will be delivered inside a transporter called “adeno-associated viral vector” (AAV). To understand how this works, think about the AADC gene like a letter that carries the instructions the brain needs to make the AADC enzyme and the AAV as the envelope that carries the letter.

AAV acts like the envelope that carries the AADC gene (the letter).

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In Parkinson’s disease, the AADC enzyme that converts levodopa to dopamine decreases. This means the brain cannot make as much dopamine. Dopamine is what helps your brain control your movements.

Voyager’s VY-AADC02
Voyager Therapeutics’ experimental gene therapy is intended to put the AADC gene into the brain where the AADC enzyme is needed to convert levodopa to dopamine.