Streamlined determination of 3-O-methyldopa in dried blood spots: Prospective screening for aromatic l-amino-acid decarboxylase deficiency

BACKGROUND: Aromatic L-amino-acid decarboxylase (AADC) deficiency diagnosis is often delayed by low disease awareness and specific laboratory examinations. We demonstrated that an elevated concentration of L-dopa metabolite 3-O-methyldopa (3-OMD) in dried blood spots could be integrated into a newborn screening program to detect AADC deficiency. For samples exceeding the pre-defined cutoffs, an additional spot was punched from the original filter paper for second-tier 3-OMD measurement by high performance liquid chromatography (HPLC)-MS/MS assay. Newborns with a 3-OMD concentration exceeding 500 ng/mL were referred for confirmatory testing. RESULTS: From Feb. 2020 to Dec. 2022, 157,371 newborns were screened for AADC deficiency. Eight newborns exhibited an elevated 3-OMD concentration (839-5170 ng/mL). Among them, six newborns were confirmed to carry two pathogenic DDC variants, indicating an incidence of AADC deficiency of ∼1:26,000 (95% confidence interval: 1 in 12,021 to 1 in 57,228). During the follow-up period, all six patients developed typical symptoms of AADC deficiency. CONCLUSION: The screening for 3-OMD, a target for AADC deficiency, could be easily integrated into the existing newborn screening programs and facilitate the future application for early diagnosis and effective treatment.