Grant: Operating Grant: SickKids-CIHR-IHDCYH New Investigator Grants

Leigh Syndrome is a neurometabolic disorder of infancy associated with deficiencies in mitochondrial oxidative phosphorylation. Leigh Syndrome, French-Canadian (LSFC) type is an autosomal recessive form characterized by neurodegenerative lactic acidosis. LSFC patients experience unpredictable metabolic and neurological crises that cause early childhood mortality. LSFC was first described in the Saguenay-Lac-Saint-Jean region, where 1 in 23 inhabitants carry a founder pathogenic mutation in the LRPPRC gene, c.1061C>T, p.(Ala354Val), resulting in a high disease prevalence of 1:2,000 newborns. Despite joint efforts by clinicians, researchers, and LSFC patient families to understand disease etiology, finding a treatment for LSFC patients remains an unmet medical need in Canada. Here, we explore two independent avenues to LSFC therapeutics. First, a combined in silico-in vitro CRISPR-knockout screening approach will be used to identify gene knockouts relieving disease-associated phenotypes in LSFC patient cells. After selecting potential druggable targets, we will find available inhibitors in drug repurposing repositories and test their ability to alleviate disease phenotypes in LSFC patient-derived fibroblasts. Second, we propose a gene therapy strategy; we will evaluate the efficiency of CRISPR-dependent adenosine base editors in correcting the founder c.1061C>T, p.(Ala354Val) mutation in LSFC patient-derived fibroblasts and reverting disease-associated phenotypes. In addition, in the absence of therapies for genetic disorders, medical genetic services for LSFC have minimized the disease's impact. However, the increasing number of variants of uncertain significance in LRPPRC complicates genetic counselling in Canada and worldwide. Hence, we will perform in situ deep mutagenesis to functionally characterize genetic variants in LRPPRC. Functional scores will be combined with clinical data and computational predictions to provide systematic variant interpretation for public repositories of clinical variation (ClinVar). Our research will explore therapeutic interventions for LSFC patients and refine genetic counselling and diagnostic tools hence improving the outlook for LSFC in Canada.