Newborn screening for aromatic l-amino-acid decarboxylase deficiency

Chien YH, Chen PW, Lee NC, Hsieh WS, Chiu PC, Hwu WL, Tsai FJ, Lin SP, Chu SY, Jong YJ, Chao MC. 3-O-methyldopa levels in newborns: Result of newborn screening for aromatic l-amino-acid decarboxylase deficiency. Mol Genet Metab. 2016 Aug;118(4):259-63.

Abstract

BACKGROUND:

The diagnosis of aromatic l-amino-acid decarboxylase (AADC) deficiency is often delayed because a cerebrospinal fluid analysis is required to detect a neurotransmitter deficiency. We here demonstrated that an elevated concentration of l-dopa metabolite 3-O-methyldopa (3-OMD) in dried blood spots could be integrated into newborn screening program to precisely predict AADC deficiency.

METHODS:

After obtaining parental consent, an additional spot was punched from newborn filter paper, eluted, cleaned, and analyzed by tandem mass spectrometry. Newborns with a 3-OMD concentration exceeding 500ng/mL were referred for confirmatory testing.

RESULTS:

From September 2013 to December 2015, 127,987 newborns were screened for AADC deficiency. The mean 3-OMD concentration in these newborns was 88.08ng/mL (SD=27.74ng/mL). Four newborns exhibited an elevated 3-OMD concentration (range, 939-3241ng/mL). All four newborns were confirmed to carry two pathologic DDC mutations, indicating an incidence of AADC deficiency of 1:32,000. During the follow-up period, three patients developed typical symptoms of AADC deficiency. Among 16 newborns with mildly elevated 3-OMD levels, six were heterozygous for the DDC IVS6+4A>T mutation.

CONCLUSION:

Newborn screening of AADC deficiency was achieved with a 100% positive-predictive rate. An association for gestational age could be further elucidated.

Chen PW, Lee NC, Chien YH, Wu JY, Wang PC, Hwu WL. Diagnosis of aromatic L-amino acid decarboxylase deficiency by measuring 3-O-methyldopa concentrations in dried blood spots. Clin Chim Acta. 2014 Apr 20;431:19-22.

Abstract

BACKGROUND:

Inherited 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.

METHODS:

3-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).

RESULTS:

3-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.

CONCLUSIONS:

We 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.