The erroneous conclusion, made earlier, was caused by technical errors in how the mutation was identified in a population-health database
Geneticists have found zero evidence to prove that the mutation aimed to make the world’s first gene-edited babies resistant to HIV cuts life expectancy, as claimed earlier, the Nature reported.
In November 2018, He Jiankui — a biophysicist at the Southern University of Science and Technology in Shenzhen, China — reportedly made the first-ever CRISPR-edited babies. Using the gene-editing technology, he targeted gene CCR5 that codes for a protein which HIV uses to enter cells.
The biophysicist created a specific mutation in the gene, CCR5-delta32 (CCR5-Δ32), that few people naturally have — that possibly confers innate resistance to HIV.
However, Jiankui might have inadvertently shortened their life expectancy, claimed a research published in June 2019 in the journal Nature Medicine. It had suggested that people with two copies of a natural genetic mutation offering resistance to HIV could be at an increased risk of dying earlier than other people.
The authors of the paper, including Rasmus Nielsen, a population geneticist at the University of California, Berkeley, retracted the findings on October 8, 2019 citing “errors that undermined conclusion”, the Nature reported on October 14.
“I feel I have a responsibility to put the record straight for the public,” said Nielsen.
In the wake of the Nature Medicine study, several scientists conducted various studies and found no evidence to suggest that people with the mutation die early. “The erroneous conclusion about CCR5 was caused by technical errors in how the mutation was identified in a population-health database,” they noted.
In his attempt to replicate the findings, Sean Harrison, an epidemiologist at the University of Bristol, UK, identified discrepancy in the results. This followed a study by David Reich, a population geneticist at Harvard Medical School in Boston.
Neilsen and his team's analysis was based on genetic and health data from nearly 410,000 people enrolled in the UK Biobank research project. The database, however, showed fewer people with two copies of CCR5-Δ32 than predicted in the evolutionary theory.
Reich's study found that the number of people with two copies of the CCR5-Δ32 mutation in the biobank was undercounted.
It is because the method that “measured the variant they were tracking did not always identify its target sequence”, Nielsen noted. “There were checks we could have done and should have done that we didn’t do. We missed the fact that there was a genotyping error,” he said.
Another study, which tracked genome databases of nearly 300,000 people from Iceland and Finland, also found no evidence.
However, the discrepancies identified with the gene variant do not mean a green light for gene editing of CCR5, the researchers stressed.
“It’s very reasonable to expect that it might have a valuable function that we just don’t know how to measure. It seems very unwise to edit it out,” Reich said.
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