Treatment of Monogenic Diseases Through Gene Editing 

The significantly improved procedures of gene editing in embryonic cells, but also in germ cells and further cells by means of surgical engineering are decisively attributed to the development of the so-called Crispr-Cas9 technique. In this technique, a virus is used as a ‘vehicle’ to infiltrate an enzyme into a cell. This enzyme is then able to accurately cut out and/or complement single sequences of a genome.

Presentation of the Crispr-Cas9 technique: Doudna, Jennifer A./ Charpentier, Emmanuelle (2014): The new frontier of genome engineering with CRISPR-Cas9. Science 346 (6213): 1258096. Online Version

The application of Crispr-Cas9 in the human genome editing is currently experimental. However, a potential application on somatic, but also germ and embryonic cells is possible and was already conducted. A research team in China was able to modify the genome of human fertilized egg cells. However, the used egg cells had three pronuclei (tripronuclear zygotes) which made them unable to develop into a healthy embryo.

Liang, Puping, / Xu, Yanwen/ Zhang, Xiya et al. (2015): CRISPR/Cas9-mediated gene editing in human tripronuclear zygotes. In: Protein & Cell 6 (5), 363-372. Online Version 

Ethical concerns regarding human gene editing are currently a subject of debate within the research community. In December 2015, the organizing committee of the international summit on human gene editing published a statement in which the advocates point to the necessity of the ethical and legal support and regulation of the procedure of genome editing, both with regard to the basic research as well as the possibility of clinical application. In that respect they relate to technologies which genetically alter human germ cells as well as somatic cells of human origin.

According to the committee, the reasons for the necessity of an ethical and legal regulation are among others: 

  • the risks of inaccurate or incomplete editing of the cells including the associated risks for the carriers of the modified cells,
  • the limited possibility to predict the “harmful effects that genetic changes may have under the wide range of circumstances“ like e.g. environmental impacts on gene expression,
  • “the possibility that permanent genetic ‘enhancements’ to subsets of the population could exacerbate social inequities”,
  • “the fact that, once introduced into the human population, genetic alterations would be difficult to remove” and reverse, which also imposes risks upon “future generations who will carry the genetic alterations”.


In the light of these concerns, the advocates of the organizing committee bind themselves to refrain from using genetically modified embryos for the purpose of inducing pregnancy and call on the international research community to follow this stipulation. Moreover, they demand an alignment of the existing national legislation with respect to human genome editing in order to ensure an ethically admissible basic research and a possible clinical application across state borders.

Statement of the Organizing Committee for the International Summit on Human Gene Editing. Online Version

For a range of the related ethical concerns, see the selected articles in issue 12, volume 15, (2015) of the American Journal of Bioethics. Online Version

Cf. for an overview of the legal regulation of human genome editing in selected countries: Araki, Motoko/ Ishii, Tetsuya (2014): International regulatory landscape and integration of corrective genome editing into in vitro fertilization. In: Reproductive Biology and Endocrinology (12): 108. Online Version

Another procedure, in which the transfer of genetically conditioned diseases shall be avoided through the modification of germlines, is the so-called pronuclear and spindle transfer. In the case of diseases which are attributed to defective mitochondria in the maternal egg cell, the cell nucleus of a fertilized egg cell is inserted into another previously enucleated egg cell with 'healthy' mitochondria. This procedure as well is currently experimental and is also associated with ethical concerns with respect to possible long-term risks and the alteration of human genome. A review of the scientific as well as the ethical backgrounds is found in a publication of the Nuffield Council on Bioethics:

Nuffield Council on Bioethics (2012): Novel technique for the prevention of mitochondrial DNA disorders. An ethical review. Online Version 

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