Johnstone, Devon2020-08-252020-08-252020-08-25http://hdl.handle.net/10393/40878http://dx.doi.org/10.20381/ruor-25104Early infantile epileptic encephalopathies are a set of diseases characterized by poorly controlled or refractory seizures, contributing to, or in concert with, changes in cerebral function and neurodevelopment. Pathogenic genetic variants are a primary cause of these diseases, and many pathways have been implicated. This thesis focuses on the use of whole exome sequencing for the identification of genes implicated in three such diseases, and the use of in vitro and in vivo functional work to demonstrate pathogenicity. I identified variants in genes impacting the glycosylphosphatidylinositol (GPI) anchor biosynthesis pathway (PIGP and PIGQ) as well as confirmed the role of a novel gene associated with vitamin B6 dependent epilepsy (PLPBP), providing new mechanistic insights. I used flow cytometry to show that variants in PIGP and PIGQ impact the cell surface localization of GPI-anchored proteins, a group of important proteins on the cell surface. I used CRISPR/Cas 9 to create the first animal model of PLPHP deficiency in zebrafish, as well as provide the first evidence of mitochondrial localization of the protein and the impact of PLPBP mutations on neurotransmitters and the B6 vitamers. Treatment of plpbp-/- zebrafish larvae with pyridoxal phosphate, the active form of vitamin B6, improved survival and electrophysiological phenotypes. Finally, I characterize the phenotypic spectrum of patients with variants in each gene: 2 (PIGP), 7 (PIGQ) and 12 (PLPBP). Taken together, these findings reiterate the value of next generation sequencing for disease gene discovery, and further our understanding of the GPI-anchor and vitamin B6 pathways, facilitating future work in development of treatments for these devastating conditions.enRare diseaseGeneticsEpilepsyNext generation sequencingEpileptic encephalopathyVitamin B6IGDGPI anchorPIGPPIGQPLPBPThesis