[2] Probing this PLP-catalyzed decarboxylation, it has been discovered that there is a difference in concentration and pH dependence between substrates.

Upon cofactor binding, a large structural transformation occurs as the subunits pull closer and close the active site.

This variable effect of PLP-deficiency indicates possible isoforms of AADC with differential substrate specificity for DOPA and 5-HTP.

Dialysis studies also suggest that the potential isoform responsible for DOPA decarboxylation has a greater binding affinity for PLP than that of 5-HTP decarboxylase.

In vitro studies have confirmed PKA and PKG can both phosphorylate AADC, causing a significant increase in activity.

[10][11] In normal dopamine and serotonin (5-HT) neurotransmitter synthesis, AADC is not the rate-limiting step in either reaction.

Aromatic L-amino acid decarboxylase deficiency is associated with various symptoms as severe developmental delay, oculogyric crises and autonomic dysfunction.

To provide a basis for improving the understanding of the epidemiology, genotype–phenotype correlation and outcome of these diseases their impact on the quality of life of patients, and for evaluating diagnostic and therapeutic strategies a patient registry was established by the noncommercial International Working Group on Neurotransmitter Related Disorders (iNTD).

Significant localization of dopaminergic cells that are also immunoreactive for AADC is reported in the substantia nigra, ventral tegmental area, and the mesencephalic reticular formation.

[23] Alternative splicing events and promoters have been observed that lead to various forms of the AADC enzyme.