MicroDNA

MicroDNA is the most abundant subtype of Extrachromosomal Circular DNA (eccDNA) in humans, typically ranging from 200-400 base pairs in length and enriched in non-repetitive genomic sequences with a high density of exons.

[5] However, microDNA is currently thought to affect cellular homeostasis through transcription factor binding and have been used as a cancer biomarker.

[4][5] While the formation of microDNA is still uncertain, it has been linked to transcriptional activity and multiple DNA repair pathways.

[5] This means that some microDNA is produced through repair pathways that also occur in quiescent cells, such as from 5' ends of LINE1 elements that are known to transpose.

[3] Being 200-400 bp long, microDNA is too small to encode proteins, however, they may be important for molecular sponging.

[4][5] In general, nucleic acid molecules that are found in the bloodstream, termed circulating or cell-free, are a relatively new disease biomarker being investigated, including for diagnosis and progression of cancer.

[7] These molecules, such as cell-free DNA (cfDNA), are released into the blood upon cell death and in cases of cancer, can be identified based on the known mutations in oncogenes.

[7] Similarly, when comparing lung tissue pre- and post-tumor removal, there was no found difference in circulating microDNA key characteristics other than an unexpected trend of longer circulating microDNA sequences in cancer patients pre-tumor removal.

[7] Cell-free DNA is quickly cleared from the blood, making it a difficult cancer biomarker.