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Background/objective: Apolipoprotein E (APOE) E4 is the main genetic risk factor for Alzheimer's disease (AD). Due to the consistent association, there is interest as to whether E4 influences the risk of other neurodegenerative diseases. Further, there is a constant search for other genetic biomarkers contributing to these phenotypes, such as microtubule-associated protein tau (MAPT) haplotypes. Here, participants from the Ontario Neurodegenerative Disease Research Initiative were genotyped to investigate whether the APOE E4 allele or MAPT H1 haplotype are associated with five neurodegenerative diseases: (1) AD and mild cognitive impairment (MCI), (2) amyotrophic lateral sclerosis, (3) frontotemporal dementia (FTD), (4) Parkinson's disease, and (5) vascular cognitive impairment., Methods: Genotypes were defined for their respective APOE allele and MAPT haplotype calls for each participant, and logistic regression analyses were performed to identify the associations with the presentations of neurodegenerative diseases., Results: Our work confirmed the association of the E4 allele with a dose-dependent increased presentation of AD, and an association between the E4 allele alone and MCI; however, the other four diseases were not associated with E4. Further, the APOE E2 allele was associated with decreased presentation of both AD and MCI. No associations were identified between MAPT haplotype and the neurodegenerative disease cohorts; but following subtyping of the FTD cohort, the H1 haplotype was significantly associated with progressive supranuclear palsy., Conclusion: This is the first study to concurrently analyze the association of APOE isoforms and MAPT haplotypes with five neurodegenerative diseases using consistent enrollment criteria and broad phenotypic analysis.

Background: Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) have become the most common known cause for developing Parkinson's disease. The frequency of mutations described in the literature varies widely depending on the population studied with most reports focusing only on screening for the most common G2019S mutation in exon 41., Methods: In this study seven exons (19, 24, 25, 31, 35, 38, and 41) in LRRK2 where mutations have been reported were screened in 230 unselected Parkinson's disease patients using denaturing high-performance liquid chromatography., Results: The sequencing of samples with heteroduplex profiles revealed five novel and two known intronic sequence variants. In our cohort, we were unable to detect any of the known mutations in these exons or identify novel mutations within the LRRK2 gene., Conclusions: Therefore, despite the availability of diagnostic LRRK2 genetic testing it is unlikely to yield a positive result in this population.