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The AADC enzyme is responsible for producing two chemicals called dopamine and serotonin. These chemicals are called “neurotransmitters” because they transmit signals between brain cells called neurons. On the surface of the neurons there are specialised proteins called “receptors”. These receptors selectively bind to particular neurotransmitters such as dopamine or serotonin. This binding causes the neuron to react to the signal. In AADC deficiency the AADC enzyme does not work correctly and so very little dopamine and serotonin are produced. This means that for the neurons that use dopamine and serotonin they are not able to transmit a signal. We know that these signals are required for functions such as movement, motivation, emotion and memory. This is because these neurons work within particular pathways and circuits in the brain. These pathways grow and form connections throughout the development of the embryo and the infant. Many different signals govern this development but one signal that may be important is the neurotransmitter signal itself. Dr Wang-Tso Lee has undertaken a study to investigate in detail whether there are changes in the development of brain pathways in AADC deficiency.

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Dr Lee has developed a state-of-the-art model of AADC deficiency in the brain. This model will be extensively validated to ensure that neurotransmitter levels are low in all brain regions. Using this model he will look for changes in different neuronal pathways with a staining technique called haematoxylin and eosin or H&E staining for short. Staining in this manner allows cells such as neurons to be imaged in microscopic detail and any changes in AADC deficiency identified. He will also use a more selective technique called “immunohistochemistry”. This technique uses purified antibodies that selectively recognise components of dopamine or serotonin neurons. Using this technique it should be possible to directly examine the dopamine and serotonin pathways looking for differences that may occur in AADC deficiency. If differences in the development of these pathways are found then it may be possible to prevent them with appropriate treatment. This could involve stimulating the neurotransmitter receptors from a very young age and Dr Lee’s model would be an ideal way to test new treatment strategies.

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