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Articles by K Nguyen
Total Records ( 5 ) for K Nguyen
  F Clot , D Grabli , C Cazeneuve , E Roze , P Castelnau , B Chabrol , P Landrieu , K Nguyen , G Ponsot , M Abada , D Doummar , P Damier , R Gil , S Thobois , A. J Ward , M Hutchinson , A Toutain , F Picard , A Camuzat , E Fedirko , C San , D Bouteiller , E LeGuern , A Durr , M Vidailhet , A Brice and the French Dystonia Network

Dopa-responsive dystonia is a childhood-onset dystonic disorder, characterized by a dramatic response to low dose of l-Dopa. Dopa-responsive dystonia is mostly caused by autosomal dominant mutations in the GCH1 gene (GTP cyclohydrolase1) and more rarely by autosomal recessive mutations in the TH (tyrosine hydroxylase) or SPR (sepiapterin reductase) genes. In addition, mutations in the PARK2 gene (parkin) which causes autosomal recessive juvenile parkinsonism may present as Dopa-responsive dystonia. In order to evaluate the relative frequency of the mutations in these genes, but also in the genes involved in the biosynthesis and recycling of BH4, and to evaluate the associated clinical spectrum, we have studied a large series of index patients (n = 64) with Dopa-responsive dystonia, in whom dystonia improved by at least 50% after l-Dopa treatment. Fifty seven of these patients were classified as pure Dopa-responsive dystonia and seven as Dopa-responsive dystonia-plus syndromes. All patients were screened for point mutations and large rearrangements in the GCH1 gene, followed by sequencing of the TH and SPR genes, then PTS (pyruvoyl tetrahydropterin synthase), PCBD (pterin-4a-carbinolamine dehydratase), QDPR (dihydropteridin reductase) and PARK2 (parkin) genes. We identified 34 different heterozygous point mutations in 40 patients, and six different large deletions in seven patients in the GCH1 gene. Except for one patient with mental retardation and a large deletion of 2.3 Mb encompassing 10 genes, all patients had stereotyped clinical features, characterized by pure Dopa-responsive dystonia with onset in the lower limbs and an excellent response to low doses of l-Dopa. Dystonia started in the first decade of life in 40 patients (85%) and before the age of 1 year in one patient (2.2%). Three of the 17 negative GCH1 patients had mutations in the TH gene, two in the SPR gene and one in the PARK2 gene. No mutations in the three genes involved in the biosynthesis and recycling of BH4 were identified. The clinical presentations of patients with mutations in TH and SPR genes were strikingly more complex, characterized by mental retardation, oculogyric crises and parkinsonism and they were all classified as Dopa-responsive dystonia-plus syndromes. Patient with mutation in the PARK2 gene had Dopa-responsive dystonia with a good improvement with l-Dopa, similar to Dopa-responsive dystonia secondary to GCH1 mutations. Although the yield of mutations exceeds 80% in pure Dopa-responsive dystonia and Dopa-responsive dystonia-plus syndromes groups, the genes involved are clearly different: GCH1 in the former and TH and SPR in the later.

  F. J Swartling , M. R Grimmer , C. S Hackett , P. A Northcott , Q. W Fan , D. D Goldenberg , J Lau , S Masic , K Nguyen , S Yakovenko , X. N Zhe , H. C Flynn Gilmer , R Collins , M Nagaoka , J. J Phillips , R. B Jenkins , T Tihan , S. R Vandenberg , C. D James , K Tanaka , M. D Taylor , W. A Weiss and L. Chesler

Medulloblastoma (MB) is the most common malignant brain tumor of childhood. Sonic Hedgehog (SHH) signaling drives a minority of MB, correlating with desmoplastic pathology and favorable outcome. The majority, however, arises independently of SHH and displays classic or large cell anaplastic (LCA) pathology and poor prognosis. To identify common signaling abnormalities, we profiled mRNA, demonstrating misexpression of MYCN in the majority of human MB and negligible expression in normal cerebella. We clarified a role in pathogenesis by targeting MYCN (and luciferase) to cerebella of transgenic mice. MYCN-driven MB showed either classic or LCA pathologies, with Shh signaling activated in ~5% of tumors, demonstrating that MYCN can drive MB independently of Shh. MB arose at high penetrance, consistent with a role for MYCN in initiation. Tumor burden correlated with bioluminescence, with rare metastatic spread to the leptomeninges, suggesting roles for MYCN in both progression and metastasis. Transient pharmacological down-regulation of MYCN led to both clearance and senescence of tumor cells, and improved survival. Targeted expression of MYCN thus contributes to initiation, progression, and maintenance of MB, suggesting a central role for MYCN in pathogenesis.

  D Rendic , M Sharrow , T Katoh , B Overcarsh , K Nguyen , J Kapurch , K Aoki , I. B. H Wilson and M. Tiemeyer

Addition of fucose (Fuc) to glycoprotein N-linked glycans or in O-linkage directly to Ser/Thr residues modulates specific cell–cell interactions and cell signaling events. Vertebrates and invertebrates add Fuc in 6-linkage to the reducing terminal N-acetylglucosamine residue of N-glycans. In Drosophila and other invertebrates, Fuc can also be added in 3-linkage to the same residue. These difucosylated N-glycans are recognized by anti-horseradish peroxidase (anti-HRP) antisera, providing a well-established marker for insect neural tissue. To understand the mechanisms and consequences of tissue-specific glycan expression, we identified a single 3-fucosyltransferase (FucTA) that produces the anti-HRP epitope in Drosophila embryos. FucTA transcripts are temporally and spatially restricted to cells that express the anti-HRP epitope and are missing in a mutant that lacks neural 3-fucosylation. Transgenic expression of FucTA, but not of any other candidate 3-fucosyltransferase, rescues the anti-HRP epitope in the embryonic nervous system of this mutant. Mass spectrometric characterization of the N-glycans of Drosophila embryos overexpressing FucTA confirms that this enzyme is indeed responsible for the biosynthesis of difucosylated glycans in vivo. Whereas ectopic expression of FucTA in the larval wing disc produces mild wing notching, the heterochronic, pan-neural expression of FucTA in early differentiating neurons generates neurogenic and cell migration phenotypes; this latter effect is associated with reduced GDP-Fuc levels in the embryo and indicates that the diversion of fucosylation resources towards fucosylation of N-glycans has an impact on developmental signaling associated with O-fucosylation.

  S Burtey , D Sternberg , K Nguyen , N Philip , Y Berland and B. Dussol

A 15-year-old boy with quadriplegia and facial dysmorphia was referred to the emergency room. This was his first episode of tetraplegia. One maternal uncle had exhibited the same manifestation 20 years before. Blood test revealed severe hypokalaemia and mild hypocalcaemia. The clinical diagnosis revealed an Andersen–Tawil syndrome. Molecular tools allowed us to make the diagnosis of familial hypokalaemic periodic paralysis type 1 associated with a de novo 22q11.2 microdeletion syndrome. Our case report emphasizes the importance of molecular diagnosis in genetic diseases.

  S. E Dunn , R Bhat , D. S Straus , R. A Sobel , R Axtell , A Johnson , K Nguyen , L Mukundan , M Moshkova , J. C Dugas , A Chawla and L. Steinman

Peroxisome proliferator–activated receptors (PPARs; PPAR-, PPAR-, and PPAR-) comprise a family of nuclear receptors that sense fatty acid levels and translate this information into altered gene transcription. Previously, it was reported that treatment of mice with a synthetic ligand activator of PPAR-, GW0742, ameliorates experimental autoimmune encephalomyelitis (EAE), indicating a possible role for this nuclear receptor in the control of central nervous system (CNS) autoimmune inflammation. We show that mice deficient in PPAR- (PPAR-–/–) develop a severe inflammatory response during EAE characterized by a striking accumulation of IFN-+IL-17A and IFN-+IL-17A+ CD4+ cells in the spinal cord. The preferential expansion of these T helper subsets in the CNS of PPAR-–/– mice occurred as a result of a constellation of immune system aberrations that included higher CD4+ cell proliferation, cytokine production, and T-bet expression and enhanced expression of IL-12 family cytokines by myeloid cells. We also show that the effect of PPAR- in inhibiting the production of IFN- and IL-12 family cytokines is ligand dependent and is observed in both mouse and human immune cells. Collectively, these findings suggest that PPAR- serves as an important molecular brake for the control of autoimmune inflammation.

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