Diagnosis of aromatic l-amino acid decarboxylase deficiency by measuring 3-O-methyldopa concentrations in dried blood spots

•3-O-methyldopa (3-OMD) is a catabolic product of l-dopa.•3-OMD accumulates in patients with AADC deficiency.•3-OMD levels in dried blood spot (DBS) are stable for more than 28 days.•3-OMD levels are highly elevated in newborns and children with AADC deficiency.•3-OMD level in DBS can be used for newborn screening of AADC deficiency

BackgroundInherited defects that affect the synthesis or metabolism of neurotransmitters cause severe motor dysfunction. The diagnosis of these diseases, including aromatic l-amino-acid decarboxylase (AADC) deficiency, typically requires cerebrospinal fluid (CSF) neurotransmitter analysis. However, 3-O-methyldopa (3-OMD), which is a catabolic product of l-dopa that accumulates in individuals with AADC deficiency, can be detected in blood.Methods3-OMD concentrations were measured in dried blood spots (DBSs). One 3.2-mm punch was eluted with 90% methanol containing a deuterated internal standard (3-OMD-d3), and then analyzed using liquid chromatography–tandem mass spectrometry (LC–MS/MS).Results3-OMD in DBSs was shown to be stable for more than 28 days at 37 °C. We measured DBS 3-OMD concentrations in controls and patients with AADC deficiency. 3-OMD concentrations in normal newborns and children decreased with age. Patients with AADC deficiency revealed > 15-fold increase of DBS 3-OMD concentrations. Archive newborn screening DBS samples, obtained from 6 patients with AADC deficiency, revealed more than 19-fold increase of 3-OMD concentrations.ConclusionsWe demonstrated that DBS 3-OMD concentrations were highly elevated in newborns and children with AADC deficiency. Because 3-OMD is stable in DBS, this method can be used for both high risk and newborn screening of AADC deficiency.