Table 1.

Characteristics of various extrachromosomal circular DNA structures

Structure	Size	Characteristics	References
EcDNA	1–5 Mb	Singlets or doublets (formerly described as double minutes), harbour genes and regulatory elements. Rare in non-cancer cells	Turner et al. 2017 Deshpande et al. 2019 Verhaak et al. 2019 Wu et al. 2019
EccDNA	0.1 Kb–1 Mb	Rarely harbour genes/regulatory elements unless size allows, seen in normal and cancer cells	Møller et al. 2018 Wang et al. 2021
Telomeric circles (or C-circles)	100 bp to 30 Kb – integral multiples of 738 bp	Provide a specialised mechanism for telomere elongation via the alternative mechanism of telomere (ALT) mechanism, multiples of 738 bp	Reddel 2003 Henson et al. 2009 Basenko et al. 2010
microDNA	100–400 bp	Seen in normal mouse and human cell lines, involved in small regulatory RNAs, such as miRNA generation	Shibata et al. 2012 Paulsen et al. 2018 Noer et al. 2022
Small polydispersed circular DNA (spcDNA)	100 bp–10 Kb	Earliest description of eccDNA as described in HeLa cells, linked to genomic instability	Smith and Vinograd 1972 Regev et al. 1998