Bivariate normal limits (BVNL) methodology may improve newborn screening (NBS) for lysosomal storage disorders such as Pompe disease (PD) by decreasing the proportion of false positives without significantly affecting the false-negative rate, according to a study in the International Journal of Neonatal Screening.

Lysosomal storage diseases like PD and Krabbe disease have a typically progressive course, and therapeutic success is often reliant on an early diagnosis and a timely treatment initiation. Therefore, adequate newborn screening in the presymptomatic phase is a necessity. However, anxiety that may be faced by families with children undergoing NBS can also be a factor.

“This is the crux of the ‘false positive problem’ that would benefit from improved presymptomatic identification of diseased patients,” the authors wrote.


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BVNL is a postanalytical tool that uses a prespecified tolerable false positive rate intending to decrease anxiety due to the “false positive problem.” Furthermore, it can be applied to biomarkers that are already part of several NBS protocols, thus avoiding any extra costs.

The BVNL method has already been applied to galactocerebrosidase and psychosine to test for early childhood Krabbe disease and to assay alpha L-iduronidase to test for mucopolysaccharidoses (MPS), showing apparent success in both cases.

Based on these findings, several authors have tried to apply BVNL to PD using acid alpha-glucosidase (GAA) and elevated creatinine levels, achieving a false positive rate of 0.000013% and a positive predictive value of 63%. The authors noted that although increasing the GAA threshold value to 7.5 would eliminate all false positives, the risk of misdiagnosing some real PD cases would increase.

These findings represented an improvement with respect to previous studies; however, the results were not as satisfactory as those obtained with KD and MPS, the researchers noted. Therefore, the authors suggest searching for alternatives to creatine as a biomarker.

“Continued development of the PD ellipse with other biomarkers or statistical transformations may improve efficiency, but in its current state, would outperform the use of univariate thresholds for GAA and [creatine]. Additional variables such as birth weight, age, transfusion status, etc. may serve to improve accuracy as well,” the authors concluded.

Reference

Jalal K, Carter RL, Barczykowski A, et al. A roadmap for potential improvement of newborn screening for inherited metabolic diseases following recent developments and successful applications of bivariate normal limits for pre-symptomatic detection of MPS I, Pompe disease, and Krabbe diseaseInt J Neonatal Screen. Published online November 15, 2022. doi:10.3390/ijns8040061