New DNA pencil technique enables safer human embryo editing

Scientists have successfully tested a new genetic editing technique in human embryos known as “DNA pencil,” which offers greater precision and safety than current methods. Unlike the traditional CRISPR-Cas9 technique, which acts as molecular “scissors” by cutting both strands of the DNA helix and risking significant genetic loss or mosaicism, this new approach uses base editing.

Base editing works by attaching an enzyme to a modified Cas9 protein to convert a single chemical letter of the genome directly into another without breaking the double helix. In practical applications, researchers used this method to deactivate the NANOG gene, identifying its essential role in human fetal development. Another study applied the technique to the PCSK9 gene, associated with heart disease risk, finding that base editing produced significantly fewer unintended genomic alterations than conventional methods. Despite these advancements, the technology still faces limitations, as some tested embryos exhibited chromosomal anomalies or unintended edits.