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1.  RFT1 Deficiency in Three Novel CDG Patients 
Human mutation  2009;30(10):10.1002/humu.21085.
The medical significance of N-glycosylation is underlined by a group of inherited human disorders called Congenital Disorders of Glycosylation (CDG). One key step in the biosynthesis of the Glc3Man9Glc-NAc2-PP-dolichol precursor, essential for N-glycosylation, is the translocation of Man5GlcNAc2-PP-dolichol across the endoplasmic reticulum membrane. This step is facilitated by the RFT1 protein. Recently, the first RFT1-deficient CDG (RFT1-CDG) patient was identified and presented a severe N-glycosylation disorder. In the present study, we describe three novel CDG patients with an RFT1 deficiency. The first patient was homozygous for the earlier reported RFT1 missense mutation (c.199C4T; p.R67C), whereas the two other patients were homozygous for the missense mutation c.454A4G (p.K152E) and c.892G4A (p.E298 K), respectively. The pathogenic character of the novel mutations was illustrated by the accumulation of Man5GlcNAc2-PP-dolichol and by reduced recombinant DNase 1 secretion. Both the glycosylation pattern and recombinant DNase 1 secretion could be normalized by expression of normal RFT1 cDNA in the patients’ fibroblasts. The clinical phenotype of these patients comprised typical CDG symptoms in addition to sensorineural deafness, rarely reported in CDG patients. The identification of additional RFT1-deficient patients allowed to delineate the main clinical picture of RFT1-CDG and confirmed the crucial role of RFT1 in Man5GlcNAc2-PPdolichol translocation.
PMCID: PMC3869400  PMID: 19701946
glycosylation; CDG; RFT1; dolichol
2.  Golgi Glycosylation and Human Inherited Diseases 
The Golgi factory receives custom glycosylates and dispatches its cargo to the correct cellular locations. The process requires importing donor substrates, moving the cargo, and recycling machinery. Correctly glycosylated cargo reflects the Golgi's quality and efficiency. Genetic disorders in the specific equipment (enzymes), donors (nucleotide sugar transporters), or equipment recycling/reorganization components (COG, SEC, golgins) can all affect glycosylation. Dozens of human glycosylation disorders fit these categories. Many other genes, with or without familiar names, well-annotated pedigrees, or likely homologies will join the ranks of glycosylation disorders. Their broad and unpredictable case-by-case phenotypes cross the traditional medical specialty boundaries. The gene functions in patients may be elusive, but their common feature may include altered glycosylation that provide clues to Golgi function. This article focuses on a group of human disorders that affect protein or lipid glycosylation. Readers may find it useful to generalize some of these patient-based, translational observations to their own research.
The Golgi glycosylates and sorts intracellular protein and lipid cargos. Impaired performance by mutated Golgi resident proteins creates severe and highly variable pathologies.
PMCID: PMC3181031  PMID: 21709180
3.  Targeted PCR-based enrichment and next generation sequencing for diagnostic testing of congenital disorders of glycosylation (CDG) 
Genetics in Medicine  2011;13(11):921-932.
Congenital disorders of glycosylation (CDG) are a heterogeneous group of disorders caused by deficient glycosylation, primarily affecting the N-linked pathway. It is estimated that over 40% of CDG patients lack a confirmatory molecular diagnosis. The purpose of this study was to improve molecular diagnosis for CDG by developing and validating a next generation sequencing (NGS) panel for comprehensive mutation detection in 24 genes known to cause CDG.
NGS validation was performed on 12 positive control CDG patients. These samples were blinded as to the disease causing mutations. Both RainDance and Fluidigm platforms were used for sequence enrichment and targeted amplification. The SOLiD platform was used for sequencing the amplified products. Bioinformatic analysis was performed using NextGENe® software.
The disease causing mutations were identified by NGS for all 12 positive controls. Additional variants were also detected in three controls that are known or predicted to impair gene function and may contribute to the clinical phenotype.
We conclude that development of NGS panels in the diagnostic laboratory where multiple genes are implicated in a disorder is more cost-effective and will result in improved and faster patient diagnosis compared with a gene-by-gene approach. Recommendations are also provided for data analysis from the NGS-derived data in the clinical laboratory, which will be important for the widespread use of this technology.
PMCID: PMC3398737  PMID: 21811164
congenital disorders of glycosylation; next generation sequencing; molecular diagnostic testing; target enrichment; bioinformatics
4.  Identification of the first COG-CDG patient of Indian Origin 
Molecular genetics and metabolism  2010;102(3):364-367.
Mutations in the Conserved Oligomeric Golgi (COG) complex give rise to type II congenital disorders of glycosylation (CDG). Thus far, mutations have been identified in 6 of the 8 COG subunits. Here we present data identifying a previously reported CDG-IIx case from Singapore as a new COG4 patient with 2 novel mutations leading to p.E233X and p.L773R; with p.E233X being a de novo mutation. As a result, COG4 protein expression was dramatically reduced, while expression of the other subunits remained unaffected. Analysis of serum N-glycans revealed deficiencies in both sialylation and galactosylation. Furthermore, patient fibroblasts have impaired O-glycosylation. Importantly, patient fibroblasts exhibited a delay in Brefeldin A (BFA) induced retrograde transport, a common characteristic seen in COG deficiencies.
PMCID: PMC3058693  PMID: 21185756
N-Glycosylation; Congenital Disorders of Glycosylation; COG4
5.  SRD5A3 is required for the conversion of polyprenol to dolichol, essential for N-linked protein glycosylation 
Cell  2010;142(2):203-217.
N-linked glycosylation is the most frequent modification of secreted and membrane-bound proteins in eukaryotic cells, disruption of which is the basis of the Congenital Disorders of Glycosylation (CDG). We describe a new type of CDG caused by mutations in the steroid 5α-reductase type 3 (SRD5A3) gene. Patients have mental retardation, ophthalmologic and cerebellar defects. We found that SRD5A3 is necessary for the reduction of the alpha-isoprene unit of polyprenols to form dolichols, required for synthesis of dolichol-linked monosaccharides and the oligosaccharide precursor used for N-glycosylation. The presence of residual dolichol in cells depleted for this enzyme suggests the existence of an unexpected alternative pathway for dolichol de novo biosynthesis. Our results thus suggest that SRD5A3 is likely to be the long-sought polyprenol reductase and reveal the genetic basis of one of the earliest steps in protein N-linked glycosylation.
PMCID: PMC2940322  PMID: 20637498
N-glycosylation; dolichol; polyprenol; SRD5A3
6.  Molecular and Clinical Characterization of a Moroccan Cog7 Deficient Patient 
Molecular genetics and metabolism  2007;91(2):201-204.
Mutations in the N-linked glycosylation pathway cause rare autosomal recessive defects known as Congenital Disorders of Glycosylation (CDG). A previously reported mutation in the Conserved Oligomeric Golgi complex gene, COG7, defined a new subtype of CDG in a Tunisian family. The mutation disrupted the hetero-octomeric COG complex and altered both N- and O- linked glycosylation. Here we present clinical and biochemical data from a second family with the same mutation.
PMCID: PMC1941618  PMID: 17395513
N-glycosylation; Cog7; Congenital Disorders of Glycosylation

Results 1-6 (6)