Cell-Free DNA (cfDNA)
Definition
Short DNA fragments (~166 bp) circulating extracellularly in body fluids, shed from apoptotic and necrotic cells. In plasma, predominantly hematopoietic; in pregnancy, includes 10-15% fetal cfDNA from ~10 weeks gestation.
- Fragment size
- Approximately 166 base pairs
- Origin
- Apoptotic and necrotic cell breakdown
- Plasma source
- Predominantly hematopoietic cells
- Fetal fraction
- 10-15% of maternal plasma cfDNA from about 10 weeks gestation
- Clinical use
- Non-invasive prenatal testing
Common questions
Why is cfDNA relevant to emerging forensic phenotyping methods?+
Because cfDNA carries tissue-specific methylation patterns, researchers are exploring it alongside methylation and miRNA markers to estimate the tissue source of a body fluid stain or, in prenatal contexts, to distinguish maternal from fetal contributions.
How does cfDNA differ from the genomic DNA used in standard STR profiling?+
Standard STR profiling uses intact nuclear DNA extracted from cells in a stain or sample. cfDNA is already fragmented and circulating outside any cell, so it requires different, more sensitive extraction and sequencing approaches than routine casework STR analysis.
Related terms
- Bisulphite Conversion
- A chemical treatment that deaminates unmethylated cytosines to uracil, converting them to thymine upon PCR amplification; methylated cytosines are protected. Allows methylation...
- CpG Methylation
- Addition of a methyl group to cytosine in a CpG dinucleotide. Methylation at age-associated CpGs increases or decreases with chronological age in...
- ELOVL2 Clock
- A forensic age-estimation system based on bisulphite pyrosequencing of 5 CpG sites in the ELOVL2 gene promoter; validated in multiple independent European...
- EPIC Array (Illumina)
- The Infinium MethylationEPIC v2.0 microarray measuring methylation beta values at approximately 935,000 CpG sites genome-wide; the current standard instrument for multi-CpG age-clock...
- EpiTYPER
- Agena Bioscience (formerly Sequenom) reagent system for quantitative methylation analysis via bisulphite PCR and MALDI-TOF mass spectrometry; used for multi-CpG methylation profiling...
- HIrisPlex-S
- A 41-SNP externally visible characteristics (EVC) panel for simultaneous prediction of eye, hair, and skin colour, developed at Erasmus MC Rotterdam by...
- Horvath 353-CpG Clock
- A pan-tissue epigenetic age clock built on the methylation values of 353 CpG sites from the Illumina 450K array; developed by Steve...
- MiRNA (microRNA)
- A small non-coding RNA (21-23 nt) that regulates gene expression post-transcriptionally. Different tissues and body fluids express different miRNA sets; forensic miRNA...