Complementation cloning identifies CDG-IIc, a new type of congenital disorders of glycosylation, as a GDP-fucose transporter deficiency

Congenital disorders of glycosylation (CDG) comprise a rapidly growing grou p of inherited disorders in which glycosylation of glycoproteins is defecti ve due to mutations in genes required for the assembly of lipid-linked olig osaccharides, their transfer to nascent glycoproteins (CDG-I) or the proces sing of protein-bound glycansl(1,2) (CDG-II). Previously' a defect in the G DP-fucose import into the lumen of the Golgi was identified in a person wit h CDG (A.C.) with a general deficiency of fucosyl residues in glycoproteins (3). This patient presents the clinical features of leukocyte adhesion defi ciency type II (LAD II) including mental retardation, short stature, facial stigmata, and recurrent bacterial peripheral infections with persistently elevated peripheral leukocytes(4-7). Using a fucose-specific. lectin-staini ng procedure for detection of fucosylated glycoproteins and a retroviral cD NA library, we isolated a cDNA complementing the fucosylation defect in the patient's fibroblasts. The cDNA encodes a highly hydrophobic protein of 36 4 amino acids with multiple putative transmembrane domains. Restoration of CDP-fucose import activity in Golgi-enriched vesicles from the patient's fi broblasts verified the GDP-fucose transporter activity of this protein. We identified two missense mutations in the GDP-fucose transporter cDNA of pat ient A.C. and of two other people with LAD II. Thus complementation cloning allowed us to identify the human GDP-fucose transporter cDNA and GDP-fucos e transporter deficiency as a cause for a new type of CDG. Following the re cent recommendations(2,8) for the nomenclature for CDG, this new type is cl assified as CDG-IIc (formerly LAD II).