DNA surgery on embryos removes disease

Chinese scientists used an adapted version of a controversial gene-editing technique to correct a disease-causing mutation in human embryos, a medical first cautiously hailed by other experts yesterday.

The team used a so-called "base editor" -- an adaptation of the CRISPR-Cas9 DNA snipping tool -- to correct a single, mutated "letter" among about three billion in the intricate coding of the human genome.

The targeted mutation can cause humans to be born with beta-Thalassaemia, a potentially fatal genetic blood disorder.

"This study demonstrated the feasibility of curing genetic diseases in human... embryos by base editor system," the team wrote in the specialist journal Protein & Cell.

The journal sparked controversy when it published a paper in 2015 in which the same authors reported on experiments with CRISPR-Cas9 to modify the thalassaemia gene.

That paper led to calls for a halt to experiments involving the genetic editing of human embryos.

Many fear such technology could lead to so-called "designer babies" with desired features such as intelligence engineered into their genes.

For the new study, Puping Liang of the Sun Yat-sen University in China, and a team used a technique based on CRISPR-Cas9, which allows scientists to remove and replace a faulty strand of DNA with pinpoint precision.

Instead of using the Cas9 protein as "scissors" to eliminate the mutated "letter", they used an enzyme to change it.

DNA is the instruction booklet for cells to make and sustain life. It resembles a zipper-like spiral -- the teeth on each strand are "base pairs" of encoding "letters" that chemically match with each other.