Genetic analysis of multiple system atrophy and related movement disorders

The understanding of the pathophysiology of most neurodegenerative movement disorders has been elusive. Such is the case of multiple system atrophy (MSA) and primary familial brain calcification (PFBC). In this thesis I used a range of genetic techonologies and functional strategies to unravel the genetic basis of MSA and PFBC. First, I describe the work performed in MSA and related atypical movement disorders initially by investigating candidate genes. My key findings were: i) begative results when attempting to replicate the association between COQ2 and the risk of MSA, by Sanger sequencing the largest pathologically confirmed MSA cohort the largest pathologically confirmed MSA cohort; ii) reduced levels of Coenzyme Q10 (CoQ10) in the cerebellum of MSA patients with a cerebellar or mixed MSA subtypes when compared to normal controls and other neurodegenerative movement disorders, when I measured the levels in post-mortem brain tissue of MSA and other patients and controls by high performance liquid chromatography (HPLC); iii) identification of three C9orf72 repeat expansions and one intermediate expansion in patients presenting with a corticobasal and progressive supranuclear palsy syndrome, and confirmation of the absence of the expansion in pathologically proven MSA, corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP); iv) identification of a LRRK2 protective variant in MSA by case control analysis of genotyping of LRRK2 candidate variants. Second, I detail my work applying next generation sequencing techonologies (i.e. whole exome sequencing (WES)) to the study of genetic risk factors in MSA: i) Initially I analysed a definite MSA family and ii) later I performed the largest WES study so far in sporadic MSA. This study included 450 cases out of which 298 were pathologically confirmed. These data were first investigated for candidate genes linked to MSA, other synucleinopathies and related neurodegenerative disorders, and later by peforming a case control association study for common and rare variants. The results of this work where not able to replicate previous findings that linked MSA to COQ2 or SNCA, notwidstanding it revealed interesting candidates that require follow up. Third, I studied genetically patients with PFBC. My key findings were: i) a pathogenic SLC20A2 mutation segregating with the disease in an interesting family, found by investigating recently discovered candidate genes I identified by Sanger sequencing; ii) I detail how I studied two independent primary brain calcification consanguineous families by means of homozygosity mapping and WES. I was able to identify a homozygous nonsense mutation segregating with the disease in both families in JAM2, a gene encoding the Junction adhesion molecule 2, a tight junction protein. This is a novel gene previously unreported as a cause of human disease. Through collaborations with other scientists, I showed the absence of the expression of the JAM2 protein in a fibroblast cell line of a homozygous patient compared to a heterozygous carrier and 2 independent controls. Aditionally we studied a knock out JAM-b (ortolog of human JAM2) mouse model and showed gait abnormalities and abnormal brain histopathology. In conclusion, by applying genetic technologies and related methods, I generated important insights into the CoQ10 pathway in MSA, I generated the largest dataset of WES in MSA and I discovered a new gene for PFBC. My findings are discussed inlight of the recent literature and future directions of research into each subject.