Background: Mucopolysaccharidosis (MPS) IVA is an autosomal recessive lysosomal storage disorder caused by the deficiency of N-acetylgalactosamine-6-sulfatase (GALNS) resulting in excessive lysosomal storage of keratan sulfate. This excessive storage causes a systemic skeletal dysplasia, short stature, and joint abnormalities. Treatments for MPS IVA are available. Better outcomes are associated with early treatment, which highlights a need for newborn screening for MPS IVA.
Methods: We have conducted a newborn screening pilot program for MPS IVA since December 1, 2013. Screening involved measuring the quantity of GALNS in dried blood spots on filter paper (DBFP) from newborns using a Bio-Plex immunoassay. The amounts of fluorescence sorting detected by YAG laser with wavelengths of 532 (exciting) and 580 nm (emission) is proportional to the quantity of GALNS protein.
Results: More than 5,657 neonates have been analyzed, in those, 132 newborns had GALNS quantification less than the cut-off value (48.64 ρg/mL) at the first screening test. Most of them (n=124) were exclusive and only eight had been recalled for a second DBFP collection and GALNS quantity rechecked. The reference values were 48.64-552.4 ρg/mL. For the confirmed MPS IV patients without enzyme replacement therapy (n=11), the GALNS quantities were far less than 5% of the normal population, and ranged from 0.00 to 4.02 ρg/mL. The GALNS quantities of the carriers (n=2) were significantly reduced comparing with those of the normal values.
Conclusions: The Bio-Plex immunoassay has the potential to be adopted for newborn screening of MPS IVA. This method is reliable, sensitive, validated, simple, and cost-effective in measuring GALNS enzyme in DBFP.
