Core Viewpoint - The research highlights sildenafil as a promising candidate for treating Leigh syndrome, a severe mitochondrial disease, through a novel drug repurposing approach using patient-derived induced pluripotent stem cells [4][18]. Group 1: Disease Overview - Mitochondrial diseases, including Leigh syndrome, are rare genetic disorders caused by dysfunction in mitochondria, affecting approximately 1 in 5000 newborns globally [8]. - Leigh syndrome typically manifests in infancy or early childhood, leading to progressive neurological decline, muscle weakness, and metabolic crises, with a poor prognosis and no effective treatments currently available [8]. Group 2: Research Findings - The study identified sildenafil, a PDE5 inhibitor, as a potential treatment for Leigh syndrome through high-throughput drug screening of 5632 existing drugs [10]. - Sildenafil demonstrated significant effects in rescuing neurological features in Leigh syndrome patient-derived cells and extended the lifespan of animal models [7][12]. - Clinical trials involving six Leigh syndrome patients showed improvements in muscle strength and resistance to metabolic crises after sildenafil treatment [13]. Group 3: Mechanism of Action - Sildenafil works by inhibiting phosphodiesterase 5 (PDE5), increasing levels of cyclic guanosine monophosphate (cGMP), which activates downstream signaling pathways related to neurodevelopment and energy metabolism [15][16]. Group 4: Implications for Rare Disease Treatment - This research exemplifies a new paradigm in rare disease treatment, showcasing an efficient drug discovery pathway that significantly shortens the traditional drug development timeline and reduces associated risks and costs [18]. - The successful application of sildenafil for Leigh syndrome may pave the way for similar approaches in treating other mitochondrial diseases, leveraging patient-derived stem cell models for rapid drug screening [19].