Congenital disorders of glycosylation (CDG), an expanding group of genetic diseases related to the glycosylation of proteins and lipids, are caused by mutations in over 140 genes.1) CDG are diagnosed by genetic and glycoprotein analysis of the patients with non-specific clinical conditions such as epilepsy and developmental delay.2) Transferrin, an 80 kDa glycoprotein, is the best analyte for detecting abnormal N-glycosylation due to its low level of microheterogeneity. Here, TF is linked to congenital disorder of glycosylation.