A study of human disorders in the sialic acid synthesis pathway

GNE is a bifunctional enzyme responsible for the first committed, rate limiting step in the synthesis of sialic acid, the most common terminal monosaccharide in cellular glycosylation. Mutations in GNE are responsible for two rare human disorders, Hereditary Inclusion Body Myopathy (HIBM) and Sialuria. The hyposialylation of glycoproteins has been a focus in HIBM research based on the assumption that mutations in GNE decrease synthesis of CMP-sialic acid thereby decreasing downstream sialylation. However, glycoproteins are only one class of prevalent, sialylated molecules in mammalian tissues. Analysis of glycosphingolipids revealed aberrant expression in both in vivo and in vitro models of HIBM. Surwisingly, in a mouse model of HIBM with knock-in founder mutation M712T, mutants (GNEM712T/M 12T) display a global increase in all expressed GSL species, including sialylated gangliosides. These findings were confirmed in primary human fibroblasts isolated from four H IBM patients with mutations throughout both enzymatic domains of GNE. All patient cell lines displayed an increase in absolute amounts of all glycosphingolipids when compared to control cell lines. Furthermore an HIBM like GSL phenotype could be induced in control fibroblasts after inhibition of GNE epimerase activity with a novel imino sugar inhibitor. HIBM fibroblasts grown in the presence of this inhibitor displayed dose dependent increases in glycosphingolipid expression above already elevated levels. Treatment with ManNAc and CMP-SA, metabolites downstream of GNE epimerase, had the opposite effect lowering total GSL expression in HIBM cell lines. These results link aberrant GSL expression in HIBM directly to GNE epimerase function. Fibroblasts from patients with COG la, containing mutated phosphmannomutase, also display a global increase in GSL expression. This up-regulation is thought to be a compensatory mechanism for loss of N-linked glycans in an effort to maintain net glycosylation on the cell surface. Similarly, global increases in total GSL expression seen in HIBM may be a compensatory mechanism for decreases in N-linked sialylation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Gray Platelet Syndrome: Natural History Of A Large Patient Cohort And Locus Assignment To Chromosome 3P

Gray platelet syndrome (GPS) is an inherited bleeding disorder characterized by macrothrombocytopenia and absence of platelet alpha-granules resulting in typical gray platelets on peripheral smears. GPS is associated with a bleeding tendency, myelofibrosis, and splenomegaly. Reports on GPS are limited to case presentations. The causative gene and underlying pathophysiology are largely unknown. We present the results of molecular genetic analysis of 116 individuals including 25 GPS patients from 14 independent families as well as novel clinical data on the natural history of the disease. The mode of inheritance was autosomal recessive (AR) in 11 and indeterminate in 3 families. Using genome-wide linkage analysis, we mapped the AR-GPS gene to a 9.4-Mb interval on 3p21.1-3p22.1, containing 197 protein-coding genes. Sequencing of 1423 (69%) of the 2075 exons in the interval did not identify the GPS gene. Long-term follow-up data demonstrated the progressive nature of the thrombocytopenia and myelofibrosis of GPS resulting in fatal hemorrhages in some patients. We identified high serum vitamin B(12) as a consistent, novel finding in GPS. Chromosome 3p21.1-3p22.1 has not been previously linked to a platelet disorder; identification of the GPS gene will likely lead to the discovery of novel components of platelet organelle biogenesis. This study is registered at www.clinicaltrials.gov as NCT00069680 and NCT00369421. (Blood. 2010;116(23):4990-5001)WoSScopu

Non-specific accumulation of glycosphingolipids in GNE myopathy

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