AADCD can be diagnosed with the identification of severely decreased AADC activity in plasma.
In fact, even in heterozygous carriers, plasma AADC activity is reduced. Using L-Dopa as substrate is the standard method of measuring AADC activity as it gives a higher analytical yield than does 5-OH tryptophan (5-HTP).
Catecholamine metabolites in the blood are not useful in routine clinical practice; this measure neither diagnoses nor excludes AADCD.
With no distinctive MRI pattern, imaging is generally not beneficial in the workup of AADCD, but it should be performed in patients with neurodevelopmental delay to exclude other conditions in the differential.
Although increased prolactin in the blood has been seen in AADCD patients, normal levels do not exclude AADCD.
Learn more about AADCD diagnosis.
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Cite this: Stephen L. Nelson. Fast Five Quiz: Aromatic L-amino Acid Decarboxylase Deficiency (AADCD) Clinical Characteristics - Medscape - Aug 13, 2021.