We first confirmed CDT results by MS-based protein-level measurements with TMT-based relative quantitation: peptides from transferrin with unoccupied N-glycosylation sites were increased in PMM2-CDG (Figure 1B and Supplemental Figure 1A; supplemental material available online with this article; https://doi.org/10.1172/jci.insight.172509DS1). Here, TF is linked to isolated focal cortical dysplasia type II.