[Molecular genetics of alterations in the mitochondrial respiratory chain]

Mitochondrial biogenesis is the result of the coordinated action of two genomes, nuclear (nDNA) and mitochondrial (mtDNA). Therefore respiratory chain defects are divided into alterations of mtDNA and of nDNA. The former may be due to sporadic isolated deletions and specific duplications and mutations, which are both transmitted maternally. The nDNA disorders are inherited following a mendelian pattern and may affect genes which codify enzymes, genes which take part in the process of importing proteins, or genes involved in intergenomic communication. In the latter case, the alterations are seen in the mtDNA as multiple deletions or depletion. The characteristics of mitochondrial genetics are maternal inheritance, polyplasmia, heteroplasmia, mitotic segregation and threshold effect and largely explain the characteristic phenotype behaviour specific to these changes.