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I know, that the CRISP/Cas approach for "cutting" the human genome is not completely suitable if we can't say not suitable at all. Because we have many repeats and this approach can bring to our genome additional breaks in DNA and after DNA-repair it causes unwanted mutations. If so, why scientist still continue to play with it (See the link, only 16% success chinese scientist got) ? And what other DNA-editing mechanisms we have? I might be wrong, so correct me please.

Thanks for explanation.

Chinese Scientists Defy Ethics, Double Down on Editing Human Embryos

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    $\begingroup$ It's not clear to me what you're asking. Editing the human genome is not at all the same as editing the genome of human embryos. The vast majority of all work with CRISPR is for editing genes in isolated human cells grown in laboratories, not in people. In the laboratory setting, 16% is an excellent success rate; before CRISPR, that number was much, much lower --- small fractions of a percent. Very few scientists "play with it" in human embryos, because of the major ethical problems involved. So are you asking about molecular biology or ethics? $\endgroup$ – Roland Apr 27 '16 at 16:40
  • $\begingroup$ Ofc about molecular biology. $\endgroup$ – dshulgin Apr 28 '16 at 9:38
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    $\begingroup$ In terms of molecular biology, how do you come up with the idea that CRISPR is "not suitable" ? The success rates and level of specificity achievable with CRISPR is pretty darn revolutionary. That's why scientists continue to play with it -- in the lab, and in model organisms. Using CRISPR in humans is a whole different question though, and most scientists would say it's too early for this yet; but this depends a lot on what specific application you're thinking of. For curing a recessive genetic disorder for example, 10% success rate might be fine. You need to be more specific I think. $\endgroup$ – Roland Apr 28 '16 at 15:14
  • $\begingroup$ I'm interesting in how we can avoid unwanted mutations that CRISPR/Cas causes. $\endgroup$ – dshulgin Apr 28 '16 at 15:52
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    $\begingroup$ Well that's an entire research field ... If you're asking about the current rate of off-target effects, that can be answered (Keith Joung's paper mention by Tom is a good example). But in the study you cite, I don't see any data on off-target effects. They only looked at the CCR5 locus, and 84% of embryos that were not "successful" were either not edited at that locus, or contained indels (unsuccessful homology repair). So that is more about efficiency of homology repair, which is unrelated to Cas9 specificity. $\endgroup$ – Roland Apr 28 '16 at 17:17
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Repeats aren't the problem with CRISPR. They stop you from editing repeats and repeat-like sequences, but in principle they can be worked around through careful design of guide RNA. CRISPR techniques right now do have problems with off target effects, but these problems may yet be solved. The CRISP/Cas approach to gene editing already has a lot of different variants and is under continual improvement, so there's no reason to think it won't get better. There's also no reason to think that the 16% figure there is only influenced by the use of CRISPR/Cas - it's an experiment with lots of other variables.

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  • $\begingroup$ Could you be more clear? Under repeats i meant that our genome has thousands similar to our target sites and we have big probability of incorrect interaction with Cas protein. Can you explain your point in more details? Sorry that's still unclear for me. $\endgroup$ – dshulgin Apr 27 '16 at 16:03
  • $\begingroup$ "thousands similar to our target sites" is not true of all sites. It's true only of sites resembling repeats. Most sites in the genome can, for instance, have specific PCR primers designed against them. This would not be true if they all resembled repeats. $\endgroup$ – Dermot Harnett Apr 27 '16 at 16:15
  • $\begingroup$ "can" but is that true in general? I mean, we should have big confidence of that to process CRISPR/Cas on human's genome. $\endgroup$ – dshulgin Apr 27 '16 at 16:19
  • $\begingroup$ It is true in general yes. But not in every case. $\endgroup$ – Dermot Harnett Apr 27 '16 at 16:27
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The accuracy of CRISPR to its target is not necessarily a problem at this time, because scientists have developed a more accurate version of it, CRISPR hf, which has almost no off target effects. Here's a report on a study with a very accurate version of CRISPR

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