GALNS and mucopolysaccharidosis type 4A: This procedure, later improved on by Ullal et al. [21], not only facilitates the collection and delivery of samples to the referential laboratory for testing, but also make this procedure more suitable for the neonatal screening of MPS IV A. Recently, a study conducted by Cozma et al., measured GALNS activity on a DBS using a fluorogenic substrate and measured the reaction product by LC/MS-MS [22].