PTCD1 (pentatricopeptide repeat domain 1) is a mitochondrial matrix protein essential for proper mitochondrial gene expression and energy metabolism. Functionally, PTCD1 acts as a leucine-specific tRNA-binding protein that negatively regulates mitochondrial leucine tRNA levels and thereby restrains leucine-rich electron transport chain complexes 1. PTCD1 participates in 3'-end processing of mitochondrial tRNAs 2 and is critical for 16S rRNA stability and maturation, which are prerequisites for mitochondrial ribosome assembly and mitochondrial translation 3. Loss of PTCD1 impairs oxidative phosphorylation, forcing cells to depend on glycolysis for ATP production 4. Platelet-specific PTCD1 deletion causes thrombocytopenia and bleeding defects by compromising mitochondrial gene expression required for platelet activation and blood coagulation 5. Clinically, PTCD1 variants show enrichment in Alzheimer's disease (AD) patients, suggesting a genetic link to neurodegeneration 46. Neurons expressing AD-associated PTCD1 variants fail to maintain ATP production during metabolic stress, resulting in reduced neuronal energy homeostasis and impaired synaptic activity 4. These findings establish PTCD1 as a mitochondrial regulator whose dysfunction contributes to both blood disorders and neurodegenerative disease pathogenesis.