Mitochondrial DNA-related disorders: emphasis on mechanisms and heterogeneity

Mitochondrial diseases are a heterogeneous group of disorders that are currently the focus of intense research. The many cell functions performed by mitochondria include ATP production, calcium homeostasis, and apoptosis. One of the unique properties of mitochondria is the existence of a separate mitochondrial genome (mitochondrial DNA, mtDNA) found in varying copy numbers and containing 37 genes, 13 of them encoding proteins. All 13 mitochondrially encoded proteins form part of oxidative phosphorylation complexes through combination with approximately 100 nuclear DNA-encoded proteins. Coregulation of nDNA and mtDNA is therefore essential for mitochondrial function, and this coregulation contributes to the heterogeneity and complexity observed in mitochondrial disorders. In recent times, significant advances have been made in our understanding of mtDNA-related disorders. A comprehensive review of these studies will benefit both current and new researchers and clinicians involved in the field. This review examines the major types of mtDNA-related defects and their pathogenic mechanisms, with a special emphasis on the heterogeneity of mitochondrial disorders. Potential treatment strategies specialized for each of the disorders, including the hormone melatonin and the recent advances in gene therapy, related to their potential applications for the management of the primary mtDNA disorders are also discussed.