Abstract Parkinson’s disease (PD) is the most common neurodegenerative movement disorder and over ten million people worldwide are living with PD. To date, treatments are only symptomatic; they do not alter the inexorable progression of the disease. The most common cause of familial and idiopathic PD are mutations in leucine-rich repeat kinase 2 (LRRK2). LRRK2-associated and idiopathic PD demonstrate mitochondrial impairment, however our understanding of the molecular underpinnings of mitochondrial dysfunction in PD is limited. In our efforts to understand the underlying mechanisms driving mitochondrial dysfunction, we found that mitochondrial DNA damage is a shared phenotype amongst both LRRK2-associated and idiopathic PD. Unrepaired mitochondrial DNA damage can have major adverse cellular effects, impacting genetic and protein instability, compromising bioenergetic function, increasing reactive oxygen species, and triggering cell death. Recent preliminary studies by the Sanders lab has found that blocking kinase activity of ATM (a kinase that functions to sense, signal and promote repair of DNA damage) rescues PD-induced mitochondrial DNA damage. We further observed that ATM is activated and initiates the DNA damage response pathway. Interestingly, mitochondrial DNA repair capacity is impaired with a concomitant increase in specific mitochondrial oxidative DNA lesions. The overarching goal of the parental grant to understand how dysfunctional LRRK2 triggers the ATM-mediated DNA damage response pathway, which impairs mitochondrial DNA repair capacity, leading to an increase in mitochondrial DNA damage, ultimately promoting downstream pathogenic PD cascades. Specific to this research supplement, we have discovered that endogenous mutant LRRK2 interacts with activated ATM, and this interaction may be induced by DNA damage. Based on this data, Jennifer Liu will determine the molecular interactions and functional relationship between LRRK2 and ATM. Through this work, she will gain new technical expertise and methodology, publish impactful research, and obtain preliminary data for an F31 fellowship. Overall, this project will directly complement the parental grant and ongoing experiments in the lab to understand LRRK2‘s role in the DNA damage response and PD pathophysiology, which may have implications for the development of new therapies.