CDG (congenital disorders of glycosylation) is a group of monogenic diseases caused by mutations in genes involved in glycan synthesis. In its broadest definition, it includes congenital glycosylphosphatidylinositol deficiency and dystroglycanopathiess but generally refers to diseases involving the synthesis and modification (addition) of asparagine-linked (N-type) and mucin-type glycans [1]. Multi-organ and multisystem involvement results in a variety of symptoms, including developmental delay and epilepsy. Diagnosis is based on genetic analysis and the detection of abnormal molecular phenotypes, such as glycan defects and the presence of immature glycoforms in glycoproteins. Transferrin and apolipoprotein C-III for N- and mucin-type O-, respectively, are widely used for glycoform analysis.