According to the team behind the study, the sperm cells remained relatively healthy and still had the potential to fertilise an egg. Although the research is at an early stage, it could lead to a new way of preventing inherited diseases passed on by fathers.
'In theory all single gene disorders transmittable by the male can be treated if we are able to successfully use CRISPR/Cas9 on sperm,' lead researcher Dr Diane Choi at Weill Cornell Medicine in New York City, New York, told New Scientist magazine.
To date, a handful of groups have used genome editing to correct faulty genes in fertilised embryos. One concern with this approach is that as the cells of embryos rapidly divide, DNA may be repaired in some cells but not others, a phenomenon known as mosaicism.
In the current study, presented at the annual meeting of the European Society of Human Reproduction and Embryology, the scientists used genome editing to directly target a gene associated with male infertility in mature sperm cells. The team found a single 1100-volt electrical pulse, a fiftieth of second long, allowed the CRISPR components to break through the tough outer exterior of the sperm cells without killing them.
Although sperm motility was reduced by half, as the strongest and healthiest sperm had been selected, their swimming ability was still efficient enough to be able to fertilise an egg, without the need for ICSI.
It has not yet been shown whether the genome editing system actually works once inside the sperm cells and Dr Choi added that there is still a lot to understand and discover about the sperm nucleus. It is also possible that editing may take place after the sperm fertilises an egg, in which case mosaicism may still be a problem.
However, with arguably fewer medical and ethical concerns related to editing reproductive cells rather than human embryos, if the study proves to be successful, it could open new avenues for using genome editing to treat genetic disorders such as cystic fibrosis, sickle cell anaemia and muscular dystrophy.
'If we could do the editing in sperm, this would be fantastic,' said Professor Tony Perry of the University of Bath in the UK, a leading expert on genome editing who was not involved in the study. 'But it's a big "if". I think it's unlikely but I would love to be proved wrong,' he concluded.