Hosp Necker, APHP, Paris, France, 3Inserm U773 CR3B, Paris, France. Background: CDG are a rapidly growing group of inherited errors of metabolism aÂ¡ecting ...
J Inherit Metab Dis (2008) 31 (Suppl 1)
CONGENITAL DISORDER OF GLYCOSYLATION TYPE IK (CDG IK): A FREQUENT FORM OF CDG IN FRANCE? Dupre T1, Vuillaumier-Barrot S1, Sadou-Yaye H1, Le Bizec C1, de Lonlay P2, Moore S3, Seta N1 1 Lab Biochimie Hosp Bichat AP-HP, Paris, France, 2Dept Pediatrie, Hosp Necker, APHP, Paris, France, 3Inserm U773 CR3B, Paris, France Background: CDG are a rapidly growing group of inherited errors of metabolism a¡ecting glycan biosynthesis. Type I CDG are caused by defects in the biosynthesis of the lipid-linked oligosaccharide (LLO) required for protein N-glycosylation in the ER. Presently, 14 CDG I subtypes (CDG Ia-n) have been identi¢ed at the biochemical and molecular levels but cannot be di¡erentiated on the basis of clinical presentation alone. Therefore diagnosis must be established at the biological level. Applying a biological diagnosis strategy to untyped CDG I, 4 patients could be identi¢ed as CDG Ik. Methods: Four patients with a CDG I positive screening and exclusion of CDG Ia (normal phosphomannose activity) and Ib (normal phosphomannose isomerase), metabolic labelling of cultured ¢broblasts with 3H-mannose or 3H-glucosamine was performed in order to identify defective glycosylation steps through the characterisation of accumulated oligosaccharide intermediates. Results: We identi¢ed four patients that manifested abnormal accumulations of dolichol-PP-GlcNAc2, suggesting a de¢ciency of ALG1, the enzyme that adds the ¢rst mannose residue to LLO. ALG1 sequences derived from the 4 patients revealed 8 mutations: 3 mutations known to be causal (c.773C4T (Ser258Leu), c.434G4A (p. Gly145Asp), c.450C4G (p.Ser150Arg)) and 5 unknown mutations (c.765G4A (p.Thr255Thr), c.1129A4G (Met377Val), c.740G4T (p. Arg247Leu), c.740+5G4A, c.1263G4A (p.Cys396X)). Allelic inheritance and splicing error studies are underway. Conclusion: CDG Ik could be a frequent type of CDG I in France.
A NOVEL MUTATION IN THE COG5 LOCUS AFFECTS N- AND O- GLYCOSYLATION CAUSING CDG TYPE II Paesold-Burda P1, Troxler H1, Kleinert P1, Maag C2, Hennet T2, Malich S3, Steinmann B1, Baumgartner M1 1 University Children's Hospital, Zurich, Switzerland, 2Institute of Physiology, Zurich, Switzerland, 3Kantonsspital Aarau, Aarau, Switzerland Congenital disorders of glycosylation (CDG) are a group of autosomal recessive disorders caused by aberrant biogenesis of N-glycans. Here, we describe a patient from healthy and apparently unrelated parents presenting mental retardation, motor developmental delay and cerebral ataxia. Isoelectric focusing (IEF) of serum transferrin showed increased amounts of trisialo and disialo transferrin. Analysis of transferrin by electrospray ionization mass spectrometry revealed increased amounts of an isoform lacking one sialic acid residue. These ¢ndings are in agreement with 2D-PAGE analysis of serum alpha1-acid glycoprotein: the molecular mass remained constant, whereas a shift was observed at di¡erent isoelectric points. Analysis of the O-glycan apolipoprotein CIII by IEF and Western blot showed markedly elevated asialo apoC-III. Congenital defects a¡ecting both N- and O-glycosylation have been described in patients with a de¢ciency in one of the eight subunits of the conserved oligomeric golgi (COG) complex. In addition, mutations in the COG complex alter the distribution of golgi resident proteins. We observed that retrograde transport of the golgi resident GalT glycosyltransferase to the ER via Brefeldin A induced tubules was signi¢cantly slower in the patient ¢broblasts compared to normal cells. Sequencing of the eight Cog subunits revealed a homozygous mutation in the COG5 gene. Further characterization of the mutation will be presented.
CONGENITAL DISORDERS OF GLYCOSYLATION PRESENTING WITH NEURO-REGRESSION V|jayakumar K1, Prabhakar P1, Ganesan V1, Worthington V2, Jackson M3, Mills P4, Dupre T5, Vuillaumier-Barrot S5, Seta N5, Gru«newald S1 1 Great Ormond Street Hospital, London, UK, 2National Hospital for Neurology, London, UK, 3St Thomas' Hospital, London, UK, 4Institute for Child Health, London, UK, 5Biochimie Metabolique, Hoªpital Bichat, Paris, France Background: The majority of congenital disorders of glycosylation (CDG) present with neurological symptoms, a¡ecting motor and cognitive development. It has been thought, that CDG patients progress with time albeit to a very variable degree. We present two CDG cases with clear neuro-regression. Case reports: Patient 1 initially showed normal development. Laryngomalacia and occasional myocloni were noted at six weeks. At 4 months, the boy showed dystonic movements, central hypotonia and he lost his social smile. Seizure activity increased, evolving to multifocal drug resistant epilepsy, associated with apnoeas. Increasing swallowing di¤culties required tube feeding. MRI showed generalised lack of white matter and bilateral high signal in the thalami. He died at the age of one year. The isoelectric focusing of transferrin revealed a type I CDG pattern. Lipid linked oligosaccharide studies showed an increase of the DolP-Man 9 peak. Mutation analysis of the hALG6 gene detected a missense and a splicing mutation, con¢rming CDG-Ic. Patient 2 was born to unrelated parents. The girl's gross-motor development was initially mildly delayed. Towards the end of second year of life, a regression in di¡erent areas was observed, with loss of speech. Her gait became increasingly unsteady. IEF of transferrin and ApoCIII revealed a combined N- (CDG II pattern) and O-glycosylation defect. Total plasma glycan structure analysis showed abnormal fucosylated `hybrid type' glycans. The underlying enzymatic defect still needs to be determined. Conclusion: The di¡erential diagnosis of CDG should be considered in patients with unexplained neuro-regression.
A MOUSE MODEL FOR CONGENITAL DISORDER OF GLYCOSYLATION IA (CDG-IA) Schneider A1, Thiel C1, Gro«ne H-J2, Ko«rner C1 1 Div Metab Dis, Univ Child Hosp, Heidelberg, Germany, 2Div Cell Mol Path, Ger Cancer Res Center, Heidelberg, Germany During the last years the group of inherited multisystemic human disorders, called congenital disorders of glycosylation (CDG), notable gets into the focus of medical investigation and diagnostics. Defects within the biosynthesis of glycoproteins describe one thematic priority of metabolic diseases. CDG-Ia, the most frequent type of the CDG (more than 500 patients world wide), is evoked by mutations in the Phosphomannomutase 2 gene (PMM2), thereby leading to a severely reduced conversion of mannose-6-phosphate to mannose-1-phosphate in the cytosol. The symptoms of CDG-Ia patients include psychomotor and mental retardation, peripheral neuropathy, cerebellar atrophy, retinitis pigmentosa, hepatopathy and blood clotting problems. To investigate pathologic aspects of the disease and develop therapeutic approaches, an animal model for CDG-Ia is indispensable. For these purposes we generated mice with either a complete loss of Pmm2 activity or a weak residual enzyme activity as has been observed in all known CDG-Ia patients. Complete leakage of Pmm2 activity in the mouse leads to early embryonic lethality around day 2.5. Moreover, mating of heterozygous Pmm2-de¢cient male and female mice with WT mice revealed that maternal transmission of the Pmm2 null allele is severely impaired. Mouse models, which display residual Pmm2 activity, were generated by introduction of point mutations which are known from CDG-Ia patients. They reveal a broad spectrum of phenotypes which reach from early embryonic death (compound heterozygous mutation) to normal viability (F119L mutation).