Congenital Disorder Of Glycosylation, Type Iic

A number sign (#) is used with this entry because congenital disorder of glycosylation type IIc (CDG2C) is caused by homozygous or compound heterozygous mutation in the SLC35C1 gene (605881), which encodes a GDP-fucose transporter, on chromosome 11p11.

Description

Congenital disorder of glycosylation type IIc (CDG2C) is an autosomal recessive disorder characterized by moderate to severe psychomotor retardation, mild dysmorphism, and impaired neutrophil motility. It is a member of a group of disorders with a defect in the processing of protein-bound glycans. For a general overview of congenital disorders of glycosylation (CDGs), see CDG1A (212065) and CDG2A (212066).

The neutrophil defect in CDG2C has been referred to as 'leukocyte adhesion deficiency type II' (LAD2), which is a manifestation of the disorder; there are no cases of 'primary' LAD II (Frydman, 1996).

Etzioni and Harlan (1999) provided a comprehensive review of both LAD1 (116920) and LAD2. While the functional neutrophil studies are similar in the 2 LADs, the clinical course is milder in LAD2. Furthermore, patients with LAD2 present other abnormal features, such as growth and mental retardation, which are related to the primary defect in fucose metabolism. Delayed separation of the umbilical cord occurs in LAD1.

Clinical Features

Frydman et al. (1992) reported 2 ostensibly unrelated Arab Moslem boys, each born of a consanguineous mating, with a distinctive syndrome comprising unusual facial appearance, severe mental retardation, microcephaly, cortical atrophy, seizures, hypotonia, dwarfism, and recurrent infections with neutrophilia. Laboratory studies showed markedly decreased neutrophil motility, but normal opsonophagocytic activity. In addition, both patients were found to lack red blood cell H antigen and manifested the rare recessive Bombay (hh) phenotype encoded by the FUT1 gene (211100). These 2 individuals were the only known cases of the Bombay phenotype in Israel. Frydman et al. (1992) discussed the possibility of a pleiotropic effect of a single gene or a contiguous gene syndrome. Frydman et al. (1992) referred to the disorder as 'Rambam-Hasharon' syndrome after the Israeli areas in which the disorder was first described. In a note added in proof, Frydman et al. (1992) suggested that the disease locus was not linked to FUT1.

Etzioni et al. (1992) described 2 unrelated boys, 3 and 5 years old, with severe mental retardation, short stature, a distinctive facial appearance, and the Bombay (hh) blood phenotype. Both had had recurrent episodes of bacterial infection, mainly pneumonia, periodontitis, otitis media, and localized cellulitis without the formation of pus. Infections were associated with a high leukocyte count (30,000 to 150,000 per cubic millimeter), but a marked defect in neutrophil mobility was observed. Further characterization of the blood groups showed that they were both secretor-negative and Lewis-negative. Both boys were born of consanguineous parents, indicating autosomal recessive inheritance.

Lubke et al. (1999) described a patient with the clinical features of LAD2, including mental retardation, short stature, facial stigmata, and recurrent bacterial peripheral infections with persistently elevated peripheral leukocytes. Biochemical studies suggested that the transport of GDP-fucose into isolated Golgi vesicles of LAD2 cells was reduced.

Clinical Variability

Dauber et al. (2014) reported 2 British brothers with CDG2C. They presented in childhood with short stature and developmental delay with autistic features. Genetic analysis identified compound heterozygous mutations in the SLC35C1 gene (605881.0003 and 605881.0004). Both had recurrent otitis media in infancy, but no evidence of significant immune dysfunction and no leukocytosis. Blood type was O+. Plasma glycoproteins showed a global decrease in fucosylation, but the H antigen (Bombay blood group) and CD15s were present. Patients' granulocytes showed diminished but not absent rolling, and the rolling was faster than in controls. The findings suggested that the patients retained sufficient fucosylation activity to prevent immunologic abnormalities. The findings expanded the phenotypic spectrum of CDG2C, and indicated that short stature and developmental delay may be the sole presenting signs in this disorder.

Biochemical Features

Frydman et al. (1996) noted that several fucosylated proteoglycans were deficient in patients with Rambam-Hasharon syndrome, suggesting an inborn error of fucose metabolism. The immune defect is due to type II leukocyte adhesion deficiency resulting from lack of CD15, a fucose-containing, cell surface glycoprotein that is the ligand of E and P selectins (131210; 173610). In addition, the patients' red blood cells lack the H substance, a fucosylated glycoprotein, which is the precursor molecule of the A, B, and O blood groups (see 616093). Consequently, the patients manifest the Bombay blood type. Furthermore, patients are nonsecretors; they do not secrete ABH antigens in the saliva.

Pathogenesis

Pathogenesis of Leukocyte Adhesion Deficiency

Etzioni et al. (1992) provided a detailed discussion of the mechanism of leukocyte adhesion deficiency in CDG2C. In the normal state, neutrophil recruitment to the site of the inflammation is initiated by factors that induce the rolling of neutrophils on the blood-vessel wall, followed by firm adhesion and extravasation into the surrounding infected or inflamed tissue. The initial rolling of neutrophils is mediated by members of the selectin family, including E-selectin and P-selectin, which are expressed on the surface of activated endothelial cells, and L-selectin (153240), which is constitutively expressed on neutrophils. The carbohydrate ligands for E-selectin and P-selectin were characterized as the carbohydrate structure sialyl-Lewis X on the cell surface glycoproteins and glycolipids of the neutrophil. Subsequent activation of the rolling neutrophil results in up-regulated expression of the adhesion molecules LFA1 (153370) and MAC1 (120980), 2 members of the integrin family that bind to the glycoprotein ICAM1 (147840) on endothelial cells. This interaction is essential to both firm adhesion to the blood-vessel wall and extravasation into the surrounding tissue. The adhesion molecules LFA-1 and Mac-1 are alpha/beta heterodimers and share a common beta subunit, CD18 (600065), which is deficient in patients with LAD type I. Etzioni et al. (1992) referred to the form due to absence of the sialyl-Lewis X ligand of E-selectin as LAD type II. The 2 boys they described also had the Bombay blood phenotype, which is typically caused by a recessive gene (hh) resulting in a deficiency in red cell H antigen, a fucosylated carbohydrate. The H gene is closely linked to the secretor gene, and both genes code for distinct alpha-1,2-fucosyltransferases. Sialyl-Lewis X, the ligand for selectins, is another fucosylated carbohydrate; however, its synthesis requires an alpha-1,3-fucosyltransferase. Since these patients had deficiencies in a number of fucosylated carbohydrates whose synthesis depends on separate fucosyltransferase genes, Etzioni et al. (1992) suggested that the basic defect in type II leukocyte adhesion deficiency reflects a general defect in fucose metabolism (Lowe et al., 1990).

Price et al. (1994) reported in vivo neutrophil and lymphocyte function studies in a patient with LAD II. In later studies, Phillips et al. (1995) demonstrated that neutrophils from a LAD II patient bound minimally or not at all to recombinant E-selectin, purified platelet P-selectin, or P-selectin expressed on histamine-activated human umbilical vein endothelial cells, but had normal levels of L-selectin and CD11b/CD18 integrin, and adhered to and migrated across endothelin when CD11b/CD18 integrin was activated.

Karsan et al. (1998) localized the defect in LAD II to the de novo pathway of GDP-fucose biosynthesis by inducing cell surface expression of fucosylated glycoconjugates after exposure of lymphoblastoid cell lines from the LAD II patients to exogenous fucose. The defect was not restricted to hematopoietic cells, since similar findings were elicited in both human umbilical vein endothelial cells and fibroblasts derived from an affected abortus. Karsan et al. (1998) used these LAD II endothelial cells to examine the consequences of fucosylation of endothelial cells on the rolling of normal neutrophils in an in vitro assay. Neutrophil rolling on LPS-treated normal and LAD II umbilical vein endothelial cells was inhibited by an E-selectin monoclonal antibody at both high and low shear rates. LAD II umbilical vein endothelial cells lacking fucosylated glycoproteins supported leukocyte rolling to a similar degree as normal endothelial cells and LAD II cells that were fucose-fed. At low shear rates, an L-selectin antibody inhibited neutrophil rolling to a similar degree whether the LAD II cells had been fucose-fed or not. These findings suggested that fucosylation of nonlymphoid endothelial cells does not play a major role in neutrophil rolling and that fucose is not a critical moiety on the L-selectin ligand(s) on endothelial cells of the systemic vasculature.

Sturla et al. (1998) demonstrated that GDP-mannose 4,6-dehydratase (GMD; 602884), the first of 2 enzymes in the de novo GDP-L-fucose biosynthesis pathway, had defective activity and altered kinetics in cell lysates from a LAD2 patient compared with controls. GMD activity was intermediate in cell lysates from both parents. No mutations were identified in cDNA for GMD. The authors concluded that since the levels of immunoreactive GMD in cell lysates were comparable in the patient and controls, the biochemical deficiency of intracellular GMD activity in LAD2 may be due to mutations affecting a GMD-regulating protein.

Diagnosis

Prenatal Diagnosis

Frydman et al. (1996) stated that the mother in 1 of the families reported by Frydman et al. (1992) had 2 subsequent pregnancies which were monitored during midtrimester by cordocentesis. One fetus expressed H substance and her blood phenotype was O Rh+. The second fetus, a female, was 2 weeks smaller than expected by dates and had the Bombay blood type. The placenta of the affected fetus was small and irregular. This was the first prenatal diagnosis of the syndrome and the first case found in a female. Documentation of the syndrome in patients of both sexes and the parental consanguinity supported autosomal recessive inheritance. Two apparent recombinations between FUT1, the H gene, and FUT2 (182100), the secretor gene, suggested to Frydman et al. (1996) that this syndrome was due to a mutated gene other than FUT1, which causes multiple deficiencies of fucosylated proteoglycans.

Clinical Management

Marquardt et al. (1999) and others found that the lack of fucosylation in LAD2 fibroblasts could be corrected by adding fucose to the culture medium. Treatment of a LAD2 patient with oral fucose induced the expression of fucosylated selectin ligands on neutrophils and core fucosylation of serum glycoproteins. During 9 months of treatment, infections and fevers disappeared, leukocytosis returned to normal, and psychomotor capabilities improved. These results suggested to Luhn et al. (2001) that the LAD2 Golgi apparatus contains a low GDP-fucose import activity and that increased cytosolic levels of GDP-fucose synthesized from external fucose drive amounts of GDP-fucose into the Golgi sufficient to restore fucosylation. This suggested that either the mutant transporter is not completely inactive or there is yet another, low-efficient mechanism available.

Molecular Genetics

In fibroblasts derived from a patient with LAD2 (Marquardt et al., 1999), Luhn et al. (2001) and Lubke et al. (2001) independently identified a homozygous mutation in the SLC35C1 gene (R147C; 605881.0001). In 2 other patients with LAD2 derived from unrelated Arab families in Israel, Lubke et al. (2001) identified a homozygous mutation in the SLC35C1 gene (T308R; 605881.0002). These patients presented with a more severe growth defect and mental retardation than did the first patient.

Etzioni et al. (2002) found that all 3 of the previously described Arab-Israeli patients with CDG2C (Etzioni et al., 1992; Etzioni and Tonetti, 2000) were homozygous for a T308R mutation (605881.0002). A review of the patients' lineage revealed that 2 of the patients had great-grandmothers who were sisters. All 3 patients lived in the same area of about 10 square miles, suggesting a founder mutation. Analysis of the GDP-L-fucose transporter activity in these patients showed a significant reduction in the maximum rate of uptake into Golgi vesicles compared to control and parents' samples, whereas the Km values and amount of GDP-L-fucose transporter mRNA were comparable in all samples. Compared to the Turkish patient with the R147C mutation described by Marquardt et al. (1999), the patients with the T308R mutation had a very mild history of infectious episodes with only periodontitis as a persistent problem, had much more severe psychomotor retardation, and did not respond to treatment with fucose (Etzioni and Tonetti, 2000).

Nomenclature

Lubke et al. (2001) suggested that, consistent with the recommendations by Aebi et al. (1999) and Participants First International Workshop on CDGS (2000), LAD2 should be designated congenital disorder of glycosylation IIc (CDG2c), or CDG IIc.

Animal Model

Hellbusch et al. (2007) generated a mouse model for CDG IIc by inactivating the Slc35c1 gene. Slc35c1 -/- mice presented with severe growth retardation, elevated postnatal mortality rate, dilation of lung alveoli, and hypocellular lymph nodes. Lectin binding studies revealed a tremendous reduction of fucosylated glycoconjugates in tissues and isolated cells from Slc35c1 -/- mice. Fucose treatment of cells from different organs led to partial normalization of the fucosylation state of glycoproteins, indicating an alternative GDP-fucose transport mechanism. In vitro and in vivo leukocyte adhesion and rolling assays revealed a severe impairment of selectin P, E, and L ligand function.

Yakubenia et al. (2008) found that leukocyte rolling and adhesion in cremaster muscle venules, neutrophil migration to inflamed peritoneum, and lymphocyte homing to lymph nodes were strongly reduced in Slc35c1 -/- mice. In contrast, lymphocyte trafficking to splenic white pulp was normal. Accordingly, humoral immune responses of lymph nodes, but not of spleen, were defective. Yakubenia et al. (2008) suggested that SLC35C1-independent lymphocyte homing to spleen partially compensates for the lack of lymph node accessibility and explains why adaptive immune responses appear normal in patients with LAD II.