published_or_final_version / abstract / toc / Surgery / Master / Master of Philosophy

published_or_final_version / abstract / toc / Medicine / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Surgery / Master / Master of Philosophy

published_or_final_version / Pathology / Master / Master of Philosophy

published_or_final_version / Microbiology / Master / Master of Philosophy

published_or_final_version / Paediatrics / Master / Master of Philosophy

published_or_final_version / Ecology and Biodiversity / Master / Master of Philosophy

No description available.

Peripheral neuropathy associated with agenesis of the corpus callosum (ACCPN or HMSN/ACC) is a severe polyneuropathy affecting both the peripheral nervous system and the central nervous system. It is transmitted as an autosomal recessive trait and is particularly frequent in the French Canadian population of Quebec (Canada). The disease was linked to chromosome 15 in 1996 by Dr. Rouleau's team. / We genotyped polymorphic markers in the ACCPN candidate region on chromosome 15 in over 67 patients and 200 control individuals. Observation of affected haplotypes confirmed the presence of a founder effect in the French Canadian population. Recombination analysis reduced the candidate interval to approximately 2 cM between markers D15S1040 and ACTC on chromosome 15. Linkage disequilibrium analysis suggested the gene resides nearest marker D15S1232. A physical map of the newly refined candidate region was constructed using YAC, BAC and PAC clones. These clones were used to confirm the position of candidate ESTs and genes as being either within or outside the ACCPN candidate region. / The connexin 36 gene, which was confirmed to reside within the region, was excluded as the gene responsible for ACCPN using SSCP analysis. The SLC12A6 gene was also confirmed to reside within the candidate interval and was tested for mutations using SSCP, dHPLC and sequence analyses. We found a total of four disease-specific mutations in SLC12A6, all of which are expected to truncate the KCC3 protein (the protein produced by the SLC12A6 gene). Two of the four mutations were identified in the French Canadian population; 80 French Canadian ACCPN patients are homozygous for the c.2436delG in exon 18 and one French Canadian patient is a compound heterozygote, having the c.2436delG mutation as well as the 1584_1585delCTinsG mutation in exon 11. Two additional mutations were identified in one Turkish and one Italian family in exons 22 and 15 respectively. The effects of the c.2436delG mutation on KCC3 function was studied in X. laevis oocytes and the truncated protein is not functional. Finally, collaborators at Vanderbilt University disrupted the slc12a6 gene in the mouse and found a phenotype similar to the human disease. / Identification of SLC12A6 as the gene mutated in ACCPN will allow for accurate molecular diagnosis as well as carrier testing in the French Canadian population. It is also the first step in understanding the molecular mechanism leading to the disease.

The Hereditary Spastic Paraplegias (HSP) comprise a group of neurodegenerative diseases characterized by progressive lower limb spasticity. This disease, with a prevalence ranging from 1 to 20 in 100,000 individuals, is currently untreatable. The neuropathological hallmark is axonal degeneration of motor neurons in the corticospinal tract. However, the mechanisms of pathogenesis underlying this neurodegeneration remain poorly understood. Over the last decade, genetic studies of HSP have identified 33 loci including 14 genes. The main objective of this dissertation was to identify and characterize genes in a large North American HSP cohort. Mutation analysis of the two most common genes implicated in HSP, SPG3 and SPG4, led to the detection of nine novel mutations, including an ancestral SPG4 mutation in five French Canadian families. This screen also allowed for the molecular characterization of the p.del436N mutation in SPG3, which suggests a previously unidentified dominant-negative mechanism. Furthermore, a novel deletion in the VPS9 domain of the ALS2 gene was identified in a family with severe infantile onset HSP. In addition, linkage analysis and whole genome scan efforts resulted in the successful mapping of two novel HSP loci, SPG27 and SAX1. SAX1 represents the first locus for autosomal dominant spastic ataxia, a complicated form of HSP, with a common ancestor in Newfoundland. Finally, a positional candidate gene strategy at the SPG8 locus identified three missense mutations in a novel gene encoding strumpellin. Two mutations failed to rescue an axonal phenotype induced by morpholino knock-down of the SPG8 gene in zebrafish. Our efforts to identify and characterize HSP genes determined the underlying genetic cause in 36% of our cohort. These genetic causes include two novel loci and a novel gene. The findings are a major contribution to the characterization of the pathophysiology of HSP and significantly broaden the knowledge in the field of motor neuron disease. Analysis of the 15 known HSP genes suggests a common disease mechanism involving disrupted axonal membrane protein trafficking. Unraveling this mechanism will elucidate the functional maintenance of neurons in the corticospinal tract and will facilitate the development of therapies for HSP and related diseases.