Thorsten Marquardt

Carbohydrate-deficient glycoprotein syndrome type Ib. Phosphomannose isomerase deficiency and mannose therapy.

Phosphomannose isomerase (PMI) deficiency is the cause of a new type of carbohydrate-deficient glycoprotein syndrome (CDGS). The disorder is caused by mutations in the PMI1 gene. The clinical phenotype is characterized by protein-losing enteropathy, while neurological manifestations prevailing in other types of CDGS are absent. Using standard diagnostic procedures, the disorder is indistinguishable from CDGS type Ia (phosphomannomutase deficiency). Daily oral mannose administration is a successful therapy for this new type of CDG syndrome classified as CDGS type Ib.

A New Type of Carbohydrate-deficient Glycoprotein Syndrome Due to a Decreased Import of GDP-fucose into the Golgi

The fucosylation of glycoproteins was found to be deficient in a patient with a clinical phenotype resembling that of leukocyte adhesion deficiency type II (LAD II). While in LAD II hypofucosylation of glycoconjugates is secondary to an impaired synthesis of GDP-fucose due to a deficiency of the GDP-d-mannose-4,6-dehydratase, synthesis of GDP-fucose was normal in our patient (Körner, C., Linnebank, M., Koch, H., Harms, E., von Figura, K., and Marquardt, T. (1999) J. Leukoc. Biol., in press). Import of GDP-fucose into Golgi-enriched vesicles was composed of a saturable, high affinity and a nonsaturable component. In our patient the saturable high affinity import of GDP-fucose was deficient, while import of UDP-galactose and the activity of GDPase, which generates the nucleoside phosphate required for antiport of GDP-fucose, were normal. Addition ofl-fucose to the medium of fibroblasts restored the fucosylation of glycoproteins. We propose that this new form of carbohydrate-deficient glycoprotein syndrome is caused by impaired import of GDP-fucose into the Golgi.

Carbohydrate deficient glycoprotein syndrome type IV: deficiency of dolichyl‐P‐Man:Man 5 GlcNAc 2 ‐PP‐dolichyl mannosyltransferase

Type IV of the carbohydrate deficient glycoprotein syndromes (CDGS) is characterized by microcephaly, severe epilepsy, minimal psychomotor development and partial deficiency of sialic acids in serum glycoproteins. Here we show that the molecular defect in the index patient is a missense mutation in the gene encoding the mannosyltransferase that transfers mannose from dolichyl‐phosphate mannose on to the lipid‐linked oligosaccharide (LLO) intermediate Man5GlcNAc2‐PP‐dolichol. The defect results in the accumulation of the LLO intermediate and, due to its leaky nature, a residual formation of full‐length LLOs. N‐glycosylation is abnormal because of the transfer of truncated oligosaccharides in addition to that of full‐length oligosaccharides and because of the incomplete utilization of N‐glycosylation sites. The mannosyltransferase is the structural and functional orthologue of the Saccharomyces cerevisiae ALG3 gene.

Leukocyte adhesion deficiency II syndrome, a generalized defect in fucose metabolism

Abstract Leukocyte adhesion deficiency II has been described in only 2 patients; herein we report extensive investigation of another patient. The physical stigmata were detected during prenatal ultrasonographic investigation. Sialyl-Lewis X (sLex) was absent from the surface of polymorphonuclear neutrophils, and cell binding to E- and P-selectin was severely impaired, causing an immunodeficiency. The elevation of peripheral neutrophil counts occurred within several days after birth. A severe hypofucosylation of glycoconjugates bearing fucose in different glycosidic links was present in all cell types investigated, demonstrating that leukocyte adhesion deficiency II is not only a disorder of leukocytes but a generalized inherited metabolic disease affecting the metabolism of fucose. (J Pediatr 1999;134:681-8)

A Defect in Dolichol Phosphate Biosynthesis Causes a New Inherited Disorder with Death in Early Infancy

The following study describes the discovery of a new inherited metabolic disorder, dolichol kinase (DK1) deficiency. DK1 is responsible for the final step of the de novo biosynthesis of dolichol phosphate. Dolichol phosphate is involved in several glycosylation reactions, such as N-glycosylation, glycosylphosphatidylinositol (GPI)-anchor biosynthesis, and C- and O-mannosylation. We identified four patients who were homozygous for one of two mutations (c.295T-->A [99Cys-->Ser] or c.1322A-->C [441Tyr-->Ser]) in the corresponding hDK1 gene. The residual activity of mutant DK1 was 2%-4% when compared with control cells. The mutated alleles failed to complement the temperature-sensitive phenotype of DK1-deficient yeast cells, whereas the wild-type allele restored the normal growth phenotype. Affected patients present with a very severe clinical phenotype, with death in early infancy. Two of the patients died from dilative cardiomyopathy.

Congenital disorders of glycosylation: glycosylation defects in man and biological models for their study.

Abstract Several inherited disorders affecting the biosynthetic pathways of Nglycans have been discovered during the past years. This review summarizes the current knowledge in this rapidly expanding field and covers the molecular bases of these disorders as well as their phenotypical consequences.

Congenital Disorder of Glycosylation Type Id: Clinical Phenotype, Molecular Analysis, Prenatal Diagnosis, and Glycosylation of Fetal Proteins

Congenital disorder of glycosylation type Id is an inherited glycosylation disorder based on a defect of the first mannosyltransferase involved in N-glycan biosynthesis inside the endoplasmic reticulum. Only one patient with this disease has been described until now. In this article, a second patient and an affected fetus are described. The patient showed abnormal glycosylation of several plasma proteins as demonstrated by isoelectric focusing and Western blot. Lipid-linked oligosaccharides in the endoplasmic reticulum, reflecting early N-glycan assembly, revealed an accumulation of immature Man5GlcNAc2-glycans in fibroblasts of the patient. Chorion cells of the affected fetus showed the same characteristic lipid-linked oligosaccharides pattern. However, the fetus had a normal glycosylation of several plasma proteins. Some fetal glycoproteins are known to be derived from the mother, but even glycoproteins that do not cross the placenta were normally glycosylated in the affected fetus. Maternal or placental factors that partially compensate for the glycosylation defect in the fetal stage must be proposed and may be relevant for the therapy of these disorders in the future.

Plasma Lysosphingomyelin Demonstrates Great Potential as a Diagnostic Biomarker for Niemann-Pick Disease Type C in a Retrospective Study

Niemann-Pick disease type C (NP-C) is a devastating, neurovisceral lysosomal storage disorder which is characterised by variable manifestation of visceral signs, progressive neuropsychiatric deterioration and premature death, caused by mutations in the NPC1 and NPC2 genes. Due to the complexity of diagnosis and the availability of an approved therapy in the EU, improved detection of NP-C may have a huge impact on future disease management. At the cellular level dysfunction or deficiency of either the NPC1 or NPC2 protein leads to a complex intracellular endosomal/lysosomal trafficking defect, and organ specific patterns of sphingolipid accumulation. Lysosphingolipids have been shown to be excellent biomarkers of sphingolipidosis in several enzyme deficient lysosomal storage disorders. Additionally, in a recent study the lysosphingolipids, lysosphingomyelin (SPC) and glucosylsphingosine (GlcSph), appeared to be elevated in the plasma of three adult NP-C patients. In order to investigate the clinical utility of SPC and GlcSph as diagnostic markers, an in-depth fit for purpose biomarker assay validation for measurement of these biomarkers in plasma by liquid chromatography-tandem mass spectrometry was performed. Plasma SPC and GlcSph are stable and can be measured accurately, precisely and reproducibly. In a retrospective analysis of 57 NP-C patients and 70 control subjects, median plasma SPC and GlcSph were significantly elevated in NP-C by 2.8-fold and 1.4-fold respectively. For miglustat-naïve NP-C patients, aged 2–50 years, the area under the ROC curve was 0.999 for SPC and 0.776 for GlcSph. Plasma GlcSph did not correlate with SPC levels in NP-C patients. The data indicate excellent potential for the use of lysosphingomyelin in NP-C diagnosis, where it could be used to identify NP-C patients for confirmatory genetic testing.

Severe transient myocardial ischaemia caused by hypertrophic cardiomyopathy in a patient with congenital disorder of glycosylation type Ia

Abstract. Severely affected children with congenital disorder of glycosylation type Ia (CDG-Ia; MIM 212065) may develop hypertrophic cardiomyopathy. In this report we describe the near-death of a 10-month-old girl with CDG-Ia due to acute left-ventricular outlet obstruction caused by hypertrophic cardiomyopathy and acute dehydration. The girl had multi-organ failure and signs of severe myocardial damage mimicking myocardial infarction. Conclusion: hypertrophic cardiomyopathy contributes to the high mortality of young children with congenital disorder of glycosylation type Ia. Even if cardiomyopathy in this disease is non-obstructive, acute fluid-loss might cause left ventricular outflow tract obstruction and life-threatening myocardial ischaemia. Patients with congenital disorder of glycosylation type Ia are at risk for cardiac complications and should be monitored regularly by echocardiography.

Cardiomyopathy in congenital disorders of glycosylation

Congenital disorders of glycosylation are a group of inherited metabolic multisystem disorders characterized by defects in the glycosylation of proteins and lipids. In most cases, neuromuscular disease is present. The purpose of this study was to characterize the cardiological aspects in this disorder. From the literature, we identified six children with congenital disorders of glycosylation associated with cardiac disease. We then screened for cardiovascular manifestations 20 patients diagnosed with congenital disorders of glycosylation at our own institution. Of the 6 patients identified in the literature, 4 had hypertrophic cardiomyopathy, while in the other 2 the cardiac diagnosis was unclear. The mean age at cardiac diagnosis was 5 months, with a range from 34 weeks to 24 months. Of the patients, five had died at a mean age of 3.5 months, with a range from 1.5 to 6 months, with one documented cardiac death. Three of our 20 patients (15%) had coexistent cardiomyopathy, and in three additional patients presenting with cardiomyopathy we made the diagnosis of a congenital disorder of glycosylation. In our cohort, dilated cardiomyopathy was found in two-thirds of the patients, with hypertrophic cardiomyopathy in the other third. The mean age at cardiac diagnosis was 19 months, with a range from 0.5 to 84 months. Of these patients, two died in infancy at a mean age of 4 months, specifically at 1.5 and 7 months, due to cardiac disease, with one dying suddenly. The remaining four patients are alive with minor to severe cardiac dysfunction. We conclude that congenital disorders of glycosylation have to be considered in the differential diagnosis of children presenting with cardiomyopathy, and that all patients with congenital disorders of glycosylation should be screened for an associated cardiomyopathy. Cardiac involvement contributes significantly to morbidity and mortality, and probably to sudden cardiac death in this disorder.