Algorithm for Pompe disease newborn screening: results from the Taiwan screening program.

BACKGROUND: Pompe disease is caused by a deficiency in acid α-glucosidase (GAA) and results in progressive, debilitating, and often life-threatening symptoms. Newborn screening has led to the early diagnosis of Pompe disease, but the best algorithm for screening has not yet been established.
MATERIALS AND METHODS: GAA and neutral α-glucosidase (NAG) activities in dried blood spots (DBSs) were assayed using 4-methylumbelliferyl-β-d-glucopyranoside as the substrate. We also measure α-galactosidase A (GLA) activity in DBSs for comparison. A total of 473,738 newborns were screened for Pompe disease, and the data were analyzed retrospectively to determine the best screening algorithm.
RESULTS: The fluorescence assay used in the screening possessed good reproducibility, but the NAG/GAA ratio was superior in separating the true-positive from the false-positive cases. An NAG/GAA cutoff ratio≥60 produces a positive predictive value (PPV) of 63.4%, and in our sample, only two cases of later-onset Pompe disease would have been missed. The GLA/GAA ratio is not as effective as the NAG/GAA ratio.
CONCLUSION: A suitable control enzyme can improve the performance of newborn screening. Newborn screening for Pompe disease can be performed using the NAG/GAA ratio as a cutoff even in the presence of GAA partial deficiency.