Glycinergic neurotransmission is a major inhibitory influence in the CNS and defects are associated with paroxysmal neuromotor disorder, hyperekplexia with mutations in subunits of the inhibitory glycine receptor which facilitates postsynaptic ligand-binding, ion-channels. This study investigates the human glycinergic system by; 1) Mutation analysis of glycinergic candidate genes in hyperekplexia: the DNA sequencing of GLRAl in 88 hyperekplexia patients revealed 30 sequence variants; 21 were inherited in recessive mode or part of compound heterozygosity, indicating that recessive hyperekplexia is more common than previously expected. Further screening of the glycine transporter-2 gene (SLC6A5) as a candidate gene, 12 SLC6A5 mutations were found in 7 human hyperekplexia cases inherited predominantly by compound heterozygosity. 2) Biophysical analysis and molecular modelling of GLRAl mutations: which demonstrated that subcellular localisation defects were the major mechanism underlying recessive mutations. Other mutants typically show alterations in the dose-response curve for glycine suggestive of disrupted signal transduction. This study reports the first hyperekplexia mutation associated with leaky current suggesting tonic channel opening as a new receptor mechanism and fully-supported by molecular modelling. 3) Molecular and immunoreactive analysis of gephyrin heterogeneity in human brain: gephyrin encodes a multifunctional cytoplasmic protein important for organizing glycine and GABAa receptors at the postsynaptic membrane. Gephyrin has many different transcript isoforms and the study describes the population / distribution of gephyrin isoforms in neuronal tissues using molecular and immunohistochemical techniques. The heterogeneity of gephyrin cassettes indicates that each cassette is temporally and spatially regulated with unique patterns of glycine receptors co-localisation and we hypothesise that different gephyrin isoforms exhibit differential binding specificity affecting protein-protein interactions. This thesis describes that hyperekplexia is definitively a glycinergic disorder with several mechanism of molecular pathogenicity. Moreover, the underlying complexity of proteins, such as gephyrin, reveals further challenges in interpretating the functional significance of the neuronal heterogeneity.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:678657 |
| Date | January 2009 |
| Creators | Chung, Seo-Kyung |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://cronfa.swan.ac.uk/Record/cronfa42277 |
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