# Detection of low-frequency DNA variants by targeted sequencing of the Watson and Crick strands

Source: https://onco.cc/key-papers/paper-cohen-saferseqs-nat-biotechnol-2021/  
OnCo record `paper-cohen-saferseqs-nat-biotechnol-2021` (Key paper). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Barcoding both strands of each DNA molecule let researchers find mutations carried by fewer than 1 in 100,000 molecules.

## Summary

SaferSeqS introduces identical molecular barcodes into the Watson and Crick strands of template molecules and enriches targets by strand-specific PCR. It detects variants at frequencies below 1 in 100,000 DNA template molecules with a background mutation rate below 5 x 10^-7 mutants per base pair, can evaluate one or several amplicons, assesses limited quantities of cell-free DNA with high recovery of both strands, and reduces the error rate of existing PCR-based barcoding by more than 100-fold.

## Fields

- Kind: Key paper
- Last checked: 2026-11-04
- Journal: Nature Biotechnology
- Year: 2021
- DOI: 10.1038/s41587-021-00900-z
- Authors: Cohen JD, Douville C, Dudley JC, et al.
- Findings: Variants detected below 1 in 100,000 template molecules.; Background below 5 x 10^-7 mutants per base pair.; More than 100-fold lower error than earlier barcoding.
- What it means: Error is no longer what stops a blood test reading one rare molecule; how many molecules there are is.
- Caveats: Per-amplicon performance; few loci per assay.

## Sources

- Cohen et al., Nat Biotechnol 2021: https://doi.org/10.1038/s41587-021-00900-z
- PubMed: https://pubmed.ncbi.nlm.nih.gov/33941929/

## Connected records

- fronts: [Diagnostics & Biomarkers](https://onco.cc/fronts/diagnostics/)
- technologies: [Liquid biopsy (ctDNA)](https://onco.cc/technologies/liquid-biopsy/), [SaferSeqS (Watson and Crick strand sequencing)](https://onco.cc/technologies/saferseqs/)
- terms: [Circulating tumour DNA (ctDNA)](https://onco.cc/terms/ctdna/), [Next-generation sequencing (NGS)](https://onco.cc/terms/ngs/)
- journals: [Nature Biotechnology](https://onco.cc/journals/nature-biotechnology/)
- ideas: [Read methylation and mutation on the same cell-free DNA fragment to tell what kind of cancer is left](https://onco.cc/ideas/idea-same-fragment-methylation-and-mutation/)

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