Epilepsy effects up to 1% of the population, and up to 30% of people with epilepsy are pharmacoresistant—they continue to experience seizures despite treatment with maximal doses of multiple antiepileptic drugs. The causes of drug resistance in epilepsy remain poorly understood. In this work, I have used genetic and genomic analysis techniques to explore the causes of epilepsy pharmacoresistance. It has been reported that epilepsy pharmacoresistance results from impaired drug penetration into the epileptic focus secondary to a localized dysregulation of drug transporters. Solute carrier (SLC) transporters form the largest superfamily of multidrug transporters. I used novel in silico and stringent ex vivo strategies for identifying the SLCs that are dysregulated in the pharmacoresistant epileptic human hippocampus. I discovered that the SLCs dysregulated in the pharmacoresistant epileptic human hippocampus are either small metal ion exchangers or transporters of neurotransmitters, not antiepileptic drug transporters, and most likely contribute to pharmacoresistance by enhancing the intrinsic severity of epilepsy. This finding supports the newly-proposed and intuitive ‘intrinsic severity hypothesis’ of epilepsy pharmacoresistance. According to the intrinsic severity hypothesis, pharmacoresistance in epilepsy results from the increased dysfunction of the biological pathways which underlie epilepsy. Hence, I proceeded to perform genome-wide genetic and genomic analyses in order to find the most important pathways underlying epilepsy and pharmacoresistance in epilepsy. I performed an integrative analysis of previously published large-scale gene expression profiling studies on brain tissue from epilepsy surgery; the largest and most robust microarray analysis of brain tissue from surgery for pharmacoresistant mesial temporal lobe epilepsy; and the first-ever genome-wide association study (GWAS) of pharmacoresistant focal epilepsy. By integrating the results of the genetic and genomic studies, I was able to show that pharmacoresistance is the result of accumulation of deleterious genetic variants of increasing severity and/or numbers within the genes that constitute the core pathways underlying epilepsy. I also found that the pathways disrupted in pharmacoresistant epilepsy, at both the genetic and genomic levels, belong to many different diverse and disparate functional domains, for example ‘axon guidance’, ‘transmembrane transport of small molecules’ and ‘cell death signalling via NRAGE, NRIF and NADE’. However, using network analysis techniques, I showed that these seemingly unrelated pathways form a coherent highly interconnected network, and it can be expected that changes in one pathway in this network will have a cascading effect on the rest of the network. The most important pathways in these networks are the central ‘hub’ pathways, which I identified using betweenness centrality network analysis. I then performed the first-ever genetical genomics study in epilepsy using hippocampal samples from resective surgery for refractory mesial temporal lobe epilepsy. By integrating genome-wide genetic, genetical genomic and genomic studies, and then performing pathway, network and centrality analysis, I identified the most important putative central causal pathways underlying epilepsy pharmacoresistance: 'transmembrane transport of small molecules' and 'Deleted in colorectal cancer (DCC) mediated attractive signalling'. In conclusion, by performing genome-wide genetic, genetical genomic and genomic studies, followed by integrative analysis, pathway construction and network mapping, I have identified most important putative central causal pathways underlying epilepsy pharmacoresistance.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:666720 |
| Date | January 2014 |
| Creators | Mirza, Nasir |
| Publisher | University of Liverpool |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://livrepository.liverpool.ac.uk/2013019/ |
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