Mitochondrial point heteroplasmy is a common event observed not only in patients with mitochondrial diseases but also in healthy individuals. We here report a comprehensive investigation of heteroplasmy occurrence in human including the whole mitochondrial control region from nine different tissue types of 100 individuals. Sanger sequencing was used as a standard method and results were supported by cloning, minisequencing, and massively parallel sequencing.
Only 12% 
of all individuals showed no heteroplasmy, whereas 88% showed at least one 
heteroplasmic position within the investigated tissues. In 66% of individuals up 
to 8 positions were affected. The highest relative number of heteroplasmies was 
detected in muscle and liver (79%, 69%), followed by brain, hair, and heart 
(36.7%-30.2%). Lower percentages were observed in bone, blood, lung, and buccal 
cells (19.8%-16.2%). Accumulation of position-specific heteroplasmies was found 
in muscle (positions 64, 72, 73, 189, and 408), liver (position 72) and brain 
(partial deletion at position 71). Deeper analysis of these specific positions in 
muscle revealed a non-random appearance and position-specific dependency on age
. MtDNA heteroplasmy frequency and its potential functional importance have been underestimated in the past and its occurrence is ubiquitous and dependent at least on age, tissue, and position-specific mutation rates.