A team of scientists from the University of Virginia and University of North Carolina in the US have discovered a previously unidentified type of small circular DNA molecule occurring outside the chromosomes in mouse and human cells. The circular DNA is 200-400 base pairs in length and consists of non-repeating sequences. The new type of extra-chromosomal circular DNA (eccDNA) has been dubbed microDNA. Unlike other forms of eccDNA, in microDNA the sequences of base pairs are non-repetitive and are usually found associated with particular genes. This suggests they may be produced by micro-deletions of small sections of the chromosomal DNA.
This result suggests that the DNA found in tissue cells may exhibit more variation than previously thought, and the implication of this is that sequencing of the DNA in blood cells (which are the cells usually used for sequencing) may give misleading results if micro-deletions have occurred in the DNA of other tissues but not in blood cells. Examples in which this might be important are in genetic sequencing for autism or schizophrenia, which could be caused by incorrect functioning of certain genes in brain tissue. Many cancers are also caused by incorrect functioning of genes; in this case tumor suppressor genes, and sequencing of blood cell DNA could also give misleading results.
Excerpts from an article via PhysOrg