Читать книгу Bioethics - Группа авторов - Страница 142

Gene‐editing technologies have been around for over a decade. Zinc finger nucleases (ZFNs) and transcription activator‐like effector nucleases (TALENs), two gene‐editing technologies, were discovered in 2005 and 2010 respectively (Nuffield Council on Bioethics 2016). ZFNs and TALENs are relatively precise techniques, but have the disadvantage that they need engineered proteins to target specific sequences of the DNA, a procedure that requires time and resources (Nuffield Council on Bioethics 2016).

A new gene editing technique sparked debate early in 2015 due to its application on non‐viable human embryos by a group of Chinese scientists (Baltimore et al. 2015; Lanphier and Urnov 2015). The technique in question is CRISPR/Cas9, an RNA‐guided tool composed of two parts: clustered regularly interspaced short palindromic repeat (CRISPR) and CRISPR‐associated protein 9 (Cas9). CRISPR/Cas9 makes use of a naturally occurring defence mechanism that bacteria use to avoid harmful infections caused by pathogenic organisms (e.g. viruses). The RNA tool (CRISPR) functions as a guide for the Cas proteins to target specific parts of the genome, which are subsequently cut by the Cas proteins. These cut strands can be exploited to modify the nucleotide sequence of DNA and to insert genes at the cut site. The application of this technique to human embryos and human gametes (i.e. oocytes and sperm cells) has been widely criticised for a number of issues, but chiefly for its potential to introduce inheritable changes in the human genome (germline modification). Indeed, the issue of germline modification has catalysed the attention of many scientists and ethicists (Brokowski et al. 2015; Lander 2015; Lanphier and Urnov 2015).

This paper focuses on PGD and CRISPR³ applications to the field of assisted reproduction. In particular, it focuses on CRISPR as a potential alternative to PGD. CRISPR could represent a tool to avoid the occurrence of genetic diseases in future children through the modification of the genetic makeup of embryos created with IVF from couples with a known risk of transmitting such genetic diseases. Since using CRISPR on early embryos could give to prospective parents who are either affected by monogenic diseases or who are carriers of them a chance to avoid the transmission of these diseases to their offspring, this particular application of CRISPR can be considered a new reproductive option for parents who want to have genetically related children.