Carbohydrate-deficient glycoprotein syndromes become congenital disorders of glycosylation: An updated nomenclature for CDG

During the last few years, progress in identifying the molecular defects of the carbohydrate-deficient glycoprotein syndromes has been very rapid. Up to this date, six different gene defects have been elucidated. The plethora of defects that will eventually be identified makes it indispensable to use a simple and straightforward nomenclature for this group of diseases. A group of specialists in this field met for a round-table discussion at the “First International Workshop on CDGS” in Leuven, Belgium, November 12–13, 1999, and came up with the following recommendations. 1. CDG stands for “Congenital Disorders of Glycosylation”. 2. The disorders are divided into groups, based on the biochemical pathway affected: group I refers to defects in the initial steps of N-linked protein glycosylation. These deficiencies affect the assembly of dolichylpyrophosphate linked oligosaccharide and/or its transfer to asparagine residues on the nascent polypeptides; group II refers to defects in the processing of protein-bound glycans or the addition or other glycans to the protein. This grouping no longer refers directly to the isoelectric focusing pattern of serum transferrins or other serum glycoproteins. 3. CDG types are assigned to one of the groups and will be numbered consecutively as they are identified: Ia, Ib,...[emsp4 ], IIa, IIb,...[emsp4 ], etc. The currently distinguished types are: CDG-Ia (PMM2[emsp4 ]), CDG-Ib (MPI[emsp4 ]), CDG-Ic (ALG6[emsp4 ]), CDG-Id (ALG3[emsp4 ]), CDG-Ie (DPM1), CDG-IIa (MGAT2[emsp4 ]). 4. No new designations will be made unless the genetic defect is established. Untyped cases are considered “x” cases (CDG-x) until the genetic defect is known.