Protein-bound sugars on the surfaces of cells are important in the development of a normal embryo. The CDGS embryo has a defect in these cell surface sugars which prevent normal development of many tissues, in particular of the nervous system. I and II is now reasonably well understood. The biochemical defects in Types III and IV are as yet not known. Body components are manufactured on an assembly line made up of catalysts called enzymes.
Enzymes are proteins and a gene encodes the information needed to make a protein.
In both CDGS Types I and II, the child is born with two copies of a defective gene required for the proper manufacture of a protein catalyst. This means that during embryonic development in the mother's womb, this enzyme is not made correctly. This in turn means that sugars are not added properly to the proteins in the embryo. This in turn causes abnormal tissue and organ development. The abnormal enzymes in Types I and II are different but in both types, there is defective addition of sugar to protein.