GFUS and congenital disorder of glycosylation: To overcome the lack of targeted therapies for CDG, several treatment strategies are being investigated, mainly dietary supplementation with sugars and trace elements (e.g., vitamin), which is is the case of dietary sugar supplementation with fucose (e.g., FUT8-, GFUS- and SCL35C1-CDG) or galactose supplementation (e.g., TMEM165-, SLC39A8-, SLC35A2-, PGM1-, ALG13- and PMM2-CDG), most being administered under compassionate and off-label use programs.