PMM2 and congenital disorder of glycosylation: The most prevalent form of CDG is caused by mutations in the Phosphomannomutase 2 (PMM2) gene (Ng et al., 2024) encoding the enzyme that converts mannose-6-phosphate to mannose-1-phosphate, the initial step for all endoplasmic reticulum (ER)-based glycosylation (N-glycosylation, C- and O-mannosylation, GPI anchor biosynthesis) (Sharma et al., 2014).