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. The meeting was sponsored by the European Science Foundation.

The recommendations have been published simultaneously in:

• Glycoconjugate Journal (1999) 16 (11):669-671 (November 1999)

• Glycobiology (2000) 10 (6): iii-vi (June 2000).

Summary

(i) A new name for the family: Congenital Disorders of Glycosylation

The "Carbohydrate-Deficient Glycoprotein Syndromes" is a correct but difficult name for this expanding group of diseases. However, the acronym CDG (or CDGS) is already in common use. Therefore, CDG will be retained but re-defined as "Congenital Disorders of Glycosylation". With "congenital", attention is drawn to the fact that these are inborn disorders. Preference is given to "glycosylation" because the term "glycoprotein" restricts the definition. "Glycosylation" rather than "N-glycosylation", because it is anticipated that, in addition to defects in the synthesis or processing of N-glycans, defects which affect O- or C-glycosylation are likely to be discovered in the future. The S of "syndromes" in the acronym CDGS is no longer required since D represents "disorders".

(ii) A new classification: the disorders will be divided into groups.

Preference has been given to a division of the known types of CDG into two "groups" based on the location in the biochemical pathway in which the defect occurs. It is proposed that the first group includes all defects in N-glycosylation that affect the assembly of the dolichylpyrophosphate oligosaccharide precursor of N-glycans and/or the transfer of oligosaccharide from dolichylpyrophosphate to an asparagine residue on the nascent proteins. The second group includes all defects that are localized to steps in the processing of N-glycans or the addition of other glycans to the proteins. This suggestion would allow inclusion in the second group not only of defects in N-glycosylation but also in O- or C-glycosylation, although an alternative could be to add additional groups if and when such defects are discovered. It is stressed that this division is not linked to the cellular compartments in which these processes take place nor to the isoelectric focusing patterns of serum transferrins or other serum glycoproteins. The analysis of serum transferrin by isoelectric focusing is still an important diagnostic tool, because it allows a preliminary assignment of cases to either CDG group I or CDG group II. However, a definitive diagnosis requires additional biochemical and genetic analysis. Importantly, a normal transferrin pattern in isoelectric focusing does not exclude CDG.

(iii) A new nomenclature : CDG types are assigned to one of the groups and will be numbered consecutively as they are identified: Ia, Ib, ..., IIa, IIb, ..., etc.

A large majority of the participants opted to be conservative when naming the two new CDG groups: roman numbers will refer to the groups (I and II). Every separate CDG disease will be referred to as a "type" of CDG. In the acronym, the group and type will be separated from CDG by a hyphen, and the word "type" should be omitted (e.g. CDG-Ia). The currently distinguished types are listed in table 1.

No new types should be created unless the genetic defect is established. Cases in which the genetic defect remains to be elucidated, will be (re-)classified as CDG-x. The published cases for which a genetic defect is established, should be integrated into the above classification.