Multiple deletions of mtDNA remove the light strand origin of replication.

Idiopathic inflammatory myopathies are progressive, debilitating muscle diseases. The pathogenesis of these disorders is multifactorial and appears to include mutations of the mitochondrial genome, which are usually indicated by morphological changes of mitochondria. The vast majority of all mitochondrial DNA deletions found are located between the origins of replication in the "major region" between nt5760-nt190. Using long distance PCR and sequencing techniques, we detected deletions which were unusually large (ca. 10500-12800 bp) and show uncommon 5'-breakpoints between nt800 and nt3326. Unlike most other deletions, their breakpoints are far upstream of the "major region." The atypical location of these deletions suggests a different pathomechanism. The impact of the mitochondrial DNA deletions in the pathogenetic cascade remains uncertain.