ART4 and congenital disorder of glycosylation: Congenital Disorders of Glycosylation (CDG) are a heterogeneous group of nearly 137 genetic diseases due to defective glycoprotein and glycolipid glycan synthesis and attachment [24] Glycoprotein glycosylation defects can be divided into N-glycosylation defects, O-glycosylation defects and C-mannosylation defects.