ALG2 and congenital disorder of glycosylation: Congenital disorders of glycosylation (CDG) are an expanding group of disorders caused by defects in the glycosylation of proteins, and include more than 125 known genetic diseases.1,2) Among the various forms of CDG, those affecting N-glycosylation constitute a major subgroup, which is characterized by two types of molecular defects, i.e., a lack of glycans (CDG-I) or an abnormal glycan profile (CDG-II)3) (Fig. 1).