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Gene deleted in genome-edited babies linked to better recovery from stroke

25 February 2019
Appeared in BioNews 988

A gene called CCR5 has been shown to affect people's ability to recover after stroke. It is the same gene at the heart of the recent controversial case of genome edited babies in China. 

CCR5 plays multiple roles in the body. In HIV, the gene unlocks the cellular doorway that the virus must enter to infect the immune system. In the brain, its absence also helps neurons to form new connections. Patients born missing the CCR5 gene recovered better from mild stroke than patients with the gene, according to a paper published in the journal Cell

'This is the first time that a human gene has been linked to a better recovery from stroke,' said Dr Stanley Thomas Carmichael, a neurologist at the University of California, Los Angeles, who led the work. 

Dr Carmichael, who carried out the work alongside colleagues at Tel Aviv University, Israel, also found that stroke recovery was faster in mice treated with the existing HIV drug maraviroc, which blocks the CCR5 receptor. 

'When you suffer a stroke, part of your brain dies, severing those cells' connections with neurons in other regions. That's why stroke patients often suffer paralysis or lose speech,' Dr Carmichael said. 'When CCR5 is missing or blocked, neurons can make new connections and rewire the brain, enabling patients to regain some lost function.' 

The UCLA scientists' next step will be to launch a clinical trial testing the effectiveness of the drug maraviroc on stroke patients with the CCR5 gene. 'I do believe this is the beginning of hope [for stroke patients],' Professor Alcino Silva, a neurobiologist at UCLA and co-author of the study told Scientific American

The CCR5 gene has a controversial recent history. Late in 2018 it emerged that Dr He Jiankui, then at the Southern University of Science and Technology in China, had used CRISPR to attempt to edit the CCR5 genes of humans at the embryonic stage, allegedly to protect them against HIV infection. 

With this new study, the scientists are now asking if the twins born as a result of these experiments have also been cognitively enhanced. 

'The answer is likely yes, it did affect their brains,' Professor Silva told MIT technology review. 'The simplest interpretation is that those mutations will probably have an impact on cognitive function in the twins.'

He said that the exact effect on cognition was impossible to predict, and 'that is why it should not be done'. His reaction to the news that the CCR5 gene had been edited in Dr He's experiments was one of 'visceral repulsion and sadness', Professor Silva said. 

'Cognitive problems are one of the biggest unmet needs in medicine. We need drugs, but it's another thing to take normal people and muck with the DNA or chemistry to improve them,' he continued. 'We simply don't know enough to do it. Nature has struck a very fine balance.'

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