The study predicted that two girls who had their genes altered would die soon after they were withdrawn, the results unreliable

Last June, a study published in the journal Nature Medicine claimed to find evidence that twin gene-modified twin girls in China were at risk of premature death. Today, however, the two authors of this paper have retracted the article, meaning that its results will not be recognized.

Xinzhu Wei and Rasmus Nielsen , two researchers at the University of California, explain why the study was retracted from data-related errors. The researchers took genetic data from the UK's Biobank bank, but the method they used to count the number of people carrying two mutated copies of the CCR5-delta-32 gene caused them to underestimate.

As a result, Wei and Nielsen mistakenly thought that the number of people carrying these two variants died prematurely, so they could not participate in Biobank's database. The delta-32 mutation in the CCR5 gene is also what Chinese scientist He Jiankui aimed at creating two transgenic girls in 2018.

Experiment shakes the world

At the end of 2018, at the 2nd Summit on Human Genome Modification in Hong Kong, Chinese scientist He Jiankui claimed that he and his team used CRISPR technique to disable CCR5 gene in Hong Kong. embryo batch.

The embryos were then implanted in the womb of women. And whatever comes, must also come, the first two girls genetically modified in the world were born. He Jiankui said he chose to target CCR5 because people who lack 32 DNA characters in this gene, also known as delta-32 mutations, are actually able to fight HIV while not having any health problems. Any significant health.

Although He Jiankui has never published his research in any scientific journals, what he presented at a conference in Hong Kong showed that one of the two girls had both mutations in the same genome. of delta-32, the other one had only one mutation.

At the time of the baby's birth, He Jiankui declared that both of them were in good health. But other scientists fear the mutation that He Jiankui intentionally implements into the genome will cause problems as the two girls grow up.

There are studies showing evidence that people with delta-32 mutations on CCR5 have a higher rate of West Nile virus infection and are also more likely to die from flu infections.

He Jiankui at the 2nd Summit on human gene editing in Hong Kong last November

To further investigate the risks of installing this gene, scientists Xinzhu Wei and Rasmus Nielsen accessed Biobank's database, which contains the genome collection and health records of 500,000 British people. .

They counted people who owned two natural copies of the CCR5 gene with delta-32 mutations. The results showed that about 1% of the participants, and scientists noticed that the average death rate after life expectancy of these people is up to 21% higher than those with only one or no mutations. .

In addition, Wei and Nielsen were also surprised because the number of people they counted was too small. Therefore, they speculate that it is because the people carrying both delta-32 mutations in CCR5 died prematurely or were not physically fit to participate in the Biobank database.

That's a mistake

Even in the night when reading the research of Wei and Nielsen, Sean Harrison - an epidemiologist at the University of Bristol, UK doubted this result. He tried to re-analyze the data to see if it produced the same results as Wei and Nielsen.

And although Harrison did not have Biobank data on the genetic variation that Wei and Nielsen used to identify delta-32 carriers, he had a different way of doing that. Harrison analyzed genetic variations near delta-32, because it also allowed the prediction of absent DNA sequences, resulting in similar results.

It should have been, but Harrison didn't repeat the same results as Wei and Nielsen. He " shouted " on Twitter and then a long post on his personal blog.

Wei and Nielsen counted the number of people carrying two delta-32 mutants on CCR5.

Harrison's tweets and the information he provided caught the attention of David Reich, a population geneticist at Harvard Medical School. Reich is also doing research on CCR5. Therefore, he contacted and worked with Nielsen to review previous research.

The result was a fatal error was discovered. As it turned out, the method Wei and Nielsen used to count the number of people carrying two delta-32 mutants on CCR5 had failed, causing them to count missing.

Nielsen himself also confirmed this, denying his earlier conclusions that the mutants were harmful to its bearers, leaving them with no health to participate in the database of Biobank.

Nielsen admitted he should have checked his results with some other method, but he did not. " There are experiments that we can and should do, but we don't ," Nielsen said. " We missed a genotyping error . "

Genotyping is the process of identifying differences in an individual's genetic structure, through biological tests that check their DNA sequence and then comparing it with the sequence of another individual or reference sequence.

In their study, the genotyping method used by Wei and Nielsen did not detect all delta-32 mutations, resulting in their findings unreliable and must be withdrawn.

Just last week, a database-based study of nearly 300,000 living in Iceland and Finland found no evidence that people with two delta-32 copies would die earlier than others.

Mutations on CCR5 can prevent the HIV virus

But that doesn't mean that genomic editing is encouraged

The researchers emphasized that clarifying the results of Wei and Nielsen does not mean that they encourage further research targeting CCR5 gene editing to continue.

" It seems that editing it is not a very smart idea," said David Reich. The review results show that, in fact, we do not yet have the tools to accurately assess the consequences of gene editing, even though it is only a small variation on a single gene.

Gaétan Burgio, a geneticist at the Australian National University, said the article by Wei and Nielsen in the journal Natural Medicine actually could not predict the health of Chinese twins. Therefore, the retraction did not mean that the two girls were safer.

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