The new and accelerating technical development of the CRISPR/Cas9 system opens up for the possibility of targeted genetic modifications in germline competent human embryos. This is an avenue, which until very recently has been regarded as absolutely off limits. To cross the border between genetic modifications of somatic cells and germline cells was simply not conceivable, at least in most Western countries. Indeed, the border has not yet been crossed, but we are getting closer.
In two recent papers Chinese scientists used triploid human embryos as a ‘model’ to either treat ß-thalassemia  or to recapitulate a spontaneous mutation in the CCR5 gene , which results in resistance against HIV infections. Both targets are clearly chosen due to their potential for future therapeutic application.
Shortly after the first of the two papers was published, the Board of Directors of the ISTT posted a statement , which among other arguments contains the following sentence:
Uses of genetic engineering in human embryos should be limited to disease mitigation for those diseases where no other option is available; we reject the idea of “designer babies”.
This raises the question whether there are at all diseases where there are no other options (now or in the future). Hereditary diseases are rarely transmitted by homozygous parents, which makes preimplantation diagnostics (PID) an obvious safer and ethically far less disputed alternative. The example, ß-thalassemia reaches in very limited populations, like the Maldives, a frequency that puts about 1% of couples at risk to be double homozygous. But still, is not a CRISPR/Cas9 based hematopoietic stem cell therapy the obvious and much easier developed therapy?
However, the case of targeting CCR5 is fundamentally different. As no one can claim that being wild type for CCR5 is a disease, this is a clear designer approach. Given that we know relatively little about the function of CCR5, one might wonder how we can be sure that it is beneficial to mutate it in a world of ever changing microbial threats. It seems that developing a CCR5 blocking drug or somatic mutations ofCCR5 in HIV patients is the obvious way forward.
It is my feeling that many colleagues, some of whom I greatly admire, are beginning to accept experiments with the obvious goal to modify the human germline ‘if it is the only cure for severe diseases’. However, I have not heard one convincing example of such disease that is not in principle “treatable” or “avoidable”. Finally we should keep in mind that the Hardy-Weinberg equation ridicules all eugenic attempts to clean the population from ‘disease’ alleles.
I am increasingly concerned because the discussion in our community has, within a few months, taken an almost purely technical turn about off target risks and efficiency. We neglect many decades of thorough philosophical and ethical literature on the issue. There is more at stake than the possible treatment of a few rare diseases.
These questions are too important to just wait and see. We as ISTT members are so close to the topic that we need to have an honest and open discussion about our opinions. This blog could be a starting point and I invite/encourage you to add to this discussion.
 Liang, P. et al. Protein Cell (2015) http://dx.doi.org/10.1007/s13238-015-0153-5
 Kang, X. et al. J. Assist. Reprod. Genet. (2016) http://link.springer.com/article/10.1007%2Fs10815-016-0710-8