Doctor of Philosophy
Dr. Robert A. Hegele
Through the Finding of Rare Disease Genes in Canada (FORGE Canada) initiative, individuals affected with rare Mendelian diseases were clinically ascertained with a goal of identifying the genetic origin of their disease. Herein, I describe the methods for identifying the genetic basis of four Mendelian diseases. The application of next generation sequencing led to the discovery of non-synonymous variation in the DNA of individuals affected by rare diseases. The effects of the candidate variants were assessed using a series of functional experiments to complement the human genetics data. The variants observed in patients’ cells are extremely rare, were consistently predicted to be pathogenic by multiple in silico predictive programs, segregated with disease status in the family, and affected the biological properties of their respective gene products, as measured by functional assays.
Having successfully identified genetic variants underlying the Mendelian diseases, we sought to use the same approach to extract the genetic variation that may predispose individuals to complex diseases, primarily neurodegenerative disorders. We designed a neurodegeneration specific gene panel that utilizes next generation sequencing chemistry. We sequenced patients diagnosed with one of five neurodegenerative diseases: 1) Alzheimer’s disease; 2) amyotrophic lateral sclerosis (ALS); 3) frontotemporal dementia (FTD); 4) Parkinson’s disease; or 5) vascular cognitive impairment, as part of the Ontario Neurodegenerative Disease Research Initiative (ONDRI). We were successful in detecting rare variants in a large fraction of cases that may be related to the neurodegenerative phenotypes.
We also independently ascertained three large, unique families affected with familial ALS and FTD across multiple generations. The three families are diagnosed with ALS and/or FTD and in which the same hexanucleotide repeat expansion in the C9orf72 gene has been observed in all three pedigrees, but their phenotypes vary significantly. We sequenced affected individuals and observed several, distinct variants in these families that may explain the additional neurodegenerative phenotypes observed. In summary, the application of next generation sequencing has successfully identified novel genetic loci in both Mendelian and complex diseases.
Farhan, Sali, "Gene Discovery in Mendelian and Complex Diseases" (2016). Electronic Thesis and Dissertation Repository. 4077.