Mitochondrial DNA (mtDNA) mutations are a significant cause of inherited human disease, despite the small size of the mitochondrial genome. Recent advances have improved understanding of mtDNA genetics, its relationship to disease phenotypes, and the role of acquired mutations in aging and cancer. However, challenges remain in prevention and treatment. This review highlights current knowledge and areas for future research. Mitochondrial genetics differs from Mendelian genetics due to uniparental inheritance, multiple mtDNA copies per cell, and unique replication and transcription mechanisms. The mitochondrial genome is crucial for evolutionary genetics and forensic medicine. The increasing ability to analyze mtDNA has led to recognition of mtDNA disorders as a frequent cause of genetic disease. Estimates suggest that 1 in 3,500 people may have mtDNA disease or be at risk, with higher incidence in some cases. Mitochondrial diseases can arise from nuclear gene defects, as many mitochondrial proteins are nuclear-encoded. Mutations in nuclear genes can mimic mtDNA defects, and some nuclear disorders cause secondary mitochondrial abnormalities. The distinction between homoplasmy (all mtDNA copies identical) and heteroplasmy (mixed mtDNA genotypes) is important for disease expression, as a threshold level of mutated mtDNA is required for clinical symptoms. Mitochondrial DNA is inherited maternally, but paternal transmission has been observed in some cases. The transmission of heteroplasmic mtDNA mutations is complex, with environmental and nuclear factors influencing disease expression. The clinical features of mtDNA diseases are highly variable, affecting multiple tissues and systems. Diagnosis often requires biochemical and genetic testing, as symptoms can be non-specific. Mitochondrial DNA mutations are associated with various diseases, including Leigh syndrome, progressive external ophthalmoplegia, and diabetes. These mutations may also contribute to common diseases like hypertension and hypercholesterolemia. Research into mtDNA variants as predisposing factors for common diseases is ongoing, with studies exploring their role in conditions like Alzheimer's and Parkinson's disease. Animal models, such as transmitochondrial cybrid cells and heteroplasmic mice, have provided insights into mtDNA disease mechanisms. However, developing effective treatments remains challenging. Strategies to manipulate mtDNA levels, such as exercise, and gene-based therapies are being explored. Prevention of mtDNA disease transmission is also a focus, with techniques like preimplantation genetic diagnosis and oocyte manipulation being investigated. Mitochondrial DNA mutations are implicated in aging and cancer, with accumulating evidence of their role in mitochondrial dysfunction and disease progression. Further research is needed to clarify the mechanisms and develop effective treatments for mtDNA-related disorders.Mitochondrial DNA (mtDNA) mutations are a significant cause of inherited human disease, despite the small size of the mitochondrial genome. Recent advances have improved understanding of mtDNA genetics, its relationship to disease phenotypes, and the role of acquired mutations in aging and cancer. However, challenges remain in prevention and treatment. This review highlights current knowledge and areas for future research. Mitochondrial genetics differs from Mendelian genetics due to uniparental inheritance, multiple mtDNA copies per cell, and unique replication and transcription mechanisms. The mitochondrial genome is crucial for evolutionary genetics and forensic medicine. The increasing ability to analyze mtDNA has led to recognition of mtDNA disorders as a frequent cause of genetic disease. Estimates suggest that 1 in 3,500 people may have mtDNA disease or be at risk, with higher incidence in some cases. Mitochondrial diseases can arise from nuclear gene defects, as many mitochondrial proteins are nuclear-encoded. Mutations in nuclear genes can mimic mtDNA defects, and some nuclear disorders cause secondary mitochondrial abnormalities. The distinction between homoplasmy (all mtDNA copies identical) and heteroplasmy (mixed mtDNA genotypes) is important for disease expression, as a threshold level of mutated mtDNA is required for clinical symptoms. Mitochondrial DNA is inherited maternally, but paternal transmission has been observed in some cases. The transmission of heteroplasmic mtDNA mutations is complex, with environmental and nuclear factors influencing disease expression. The clinical features of mtDNA diseases are highly variable, affecting multiple tissues and systems. Diagnosis often requires biochemical and genetic testing, as symptoms can be non-specific. Mitochondrial DNA mutations are associated with various diseases, including Leigh syndrome, progressive external ophthalmoplegia, and diabetes. These mutations may also contribute to common diseases like hypertension and hypercholesterolemia. Research into mtDNA variants as predisposing factors for common diseases is ongoing, with studies exploring their role in conditions like Alzheimer's and Parkinson's disease. Animal models, such as transmitochondrial cybrid cells and heteroplasmic mice, have provided insights into mtDNA disease mechanisms. However, developing effective treatments remains challenging. Strategies to manipulate mtDNA levels, such as exercise, and gene-based therapies are being explored. Prevention of mtDNA disease transmission is also a focus, with techniques like preimplantation genetic diagnosis and oocyte manipulation being investigated. Mitochondrial DNA mutations are implicated in aging and cancer, with accumulating evidence of their role in mitochondrial dysfunction and disease progression. Further research is needed to clarify the mechanisms and develop effective treatments for mtDNA-related disorders.