In the context of neonatal health, MPS II Newborn Screening provides a vital early warning system for Hunter syndrome. However, first-tier enzyme activity tests often struggle with specificity due to common pseudodeficiency variants. Consequently, researchers initiated a large-scale pilot study in North Carolina to refine the diagnostic pathway. Specifically, they used LC-MS/MS to measure iduronate-2-sulfatase (I2S) enzyme activity in over 220,000 infants. Furthermore, they implemented a two-tier reflex protocol to verify low enzyme results. Initially, thirty-three newborns tested positive under the primary screening criteria. But, subsequent testing revealed that thirty-one of these babies actually had pseudodeficiency. Notably, the team confirmed only two infants with true MPS II.

Improving Specificity in MPS II Newborn Screening

Because of this high false-positive rate in enzyme assays, the study focused on endogenous non-reducing end (NRE) glycosaminoglycan (GAG) biomarkers. For instance, NRE GAG analysis successfully distinguished true disease cases from pseudodeficiencies with total accuracy. Moreover, the NRE GAG ratios showed a perfect correlation with confirmatory urinary GAG measurements. In addition, the team found elevated GAG levels exclusively in newborns with confirmed MPS II. Therefore, using this biomarker as a second-tier test is highly effective for laboratory workflows. Similarly, IDS sequencing provides essential genetic data for clinical evaluation and long-term follow-up. Ultimately, this multi-tier strategy reduces unnecessary referrals and eases parental anxiety. As a result, healthcare systems can manage clinical resources more efficiently while ensuring affected infants receive treatment faster.

Frequently Asked Questions

What is the main challenge in screening for MPS II?

The primary challenge is the high rate of pseudodeficiency. This occurs when enzyme activity appears low in laboratory tests but is sufficient to prevent disease in the patient, leading to false-positive results.

How does NRE GAG analysis improve screening?

NRE GAG analysis acts as a highly specific second-tier biomarker. It only shows elevated levels when there is a pathological accumulation of sugars, allowing clinicians to distinguish true MPS II from harmless pseudodeficiency.

Disclaimer: This content is for informational and educational purposes only and does not constitute professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Refer to the latest local and national guidelines for clinical practice.

References

Kucera KS et al. A North Carolina Newborn Screening Pilot for Mucopolysaccharidosis II: Evaluating Endogenous Non-Reducing End Glycosaminoglycan Analysis and IDS Sequencing as Higher-Tier Testing Options. Genet Med. 2026 Apr 21. doi: undefined. PMID: 42017346.

Giugliani R, et al. Newborn Screening for Mucopolysaccharidoses: Progress and Challenges. Int J Neonatal Screen. 2017;3(4):30.

Verma IC, et al. Genetic disorders in India and the need for newborn screening. Indian J Pediatr. 2015;82(9):830-838.