Genome-Editing Technologies: Concept, Pros, and Cons of Various Genome-Editing Techniques and Bioethical Concerns for Clinical Application Sikandar Hayat Khan1 1Department of Pathology, PNS HAFEEZ Hospital, Pathology E-8, Islamabad, Islamabad 44400, Pakistan The traditional healthcare system is at the doorstep for entering into the arena of molecular medicine. The enormous knowledge and ongoing research have now been able to demonstrate methodologies that can alter DNA coding. The techniques used to edit or change the genome evolved from the earlier attempts like nuclease technologies, homing endonucleases, and certain chemical methods. Molecular techniques like meganuclease, transcription activator-like effector nucleases (TALENs), and zinc-finger nucleases (ZFNs) initially emerged as genome-editing technologies. These initial technologies suffer from lower specificity due to their off-targets side effects. Moreover, from biotechnology’s perspective, the main obstacle was to develop simple but effective delivery methods for host cell entry. Later, small RNAs, including microRNA (miRNA) and small interfering RNA (siRNA), have been widely adopted in the research laboratories to replace lab animals and cell lines. The latest discovery of CRISPR/Cas9 technology seems more encouraging by providing better efficiency, feasibility, and multi-role clinical application. This later biotechnology seem to take genome engineering techniques to the next level of molecular engineering. This review generally discusses the various gene-editing technologies in terms of the mechanisms of action, advantages, and side effects. Over the last half century after post-DNA helical structure discovery, the world has seen a continuous staircase outburst of various molecular technologies, which are now heading forward toward translation into clinical and laboratory practice.1 Given the availability of sequencing platforms, acquired wisdom about the micro-mechanics at work within the genetic apparatus, and the introduction of user friendly nanotechnologies, it was possible for next-generation scientists to manipulate the genetic codes at various levels.2 Over the last two decades we saw a plethora of molecular techniques, which allowed us to edit genes or their alter pathways, allowing humans for the first time to micro-edit the DNA codes and further to alter the mRNA fate through post-transcriptional modifications.3 Principally, genome-wide editing techniques can be interpreted as methods where DNA sequences are changed by deletions, mRNA processing, and post-transcriptional modifications to result in altered gene expression, leading to functional behavior of proteins.4,5 Common to these methods are three basic steps, including mechanisms for genetic tool entry into the cell and later nucleus; altering gene transcription and onward processing function; and, finally, the endoutput in the shape of a suppressed, overexpressed, or simply an altered protein product.6,7 From a holistic point of view, the techniques involve an apparently simplistic concept involving multiple receptor-ligand interactions; varying cell entry modes like lipofection, sonification, and transfection; and further downstream pathway effects. Furthermore, these technologies are variable in terms of their specificity and sensitivity, off-target effects, finances, and technique expertise. The body’s immune response to accept the foreign genetic elements within the cells can lead to the rejection of foreign tissues. Moreover, molecular knowledge, in terms of methodology differences, defining targetable diseases, innovative nanotechnology tools for gene editing, and ethical aspects, also needs to be understood. The platforms for these technologies are improving every day, with a plethora of new data appearing due to technology miniaturization and automation and newer discoveries to improve the yield and specificity of an edited product. Alongside the developmental improvement in genome-wide engineering the regulatory work-up, standardization protocols need to be devised to reduce inter and intra-method imprecision, defining the indications and contraindications of every technique to help improve the concept of personalized medicine. This review briefly explains the available technologies, provides comparison and contrast between different genome-editing methods, and identifies some newer versions of genome editing with possible bioethical concerns. Review Methodology PubMed searches with the keywords genome-editing techniques or gene-editing techniques in the last 10 and 5 years yielded a total of 4,466 and 4,054 references, except some historical and related references. Specific searches for articles dealing with specific genome-editing methods included conventional genome-editing systems (n = 100), https://doi.org/10.1016/j.omtn.2019.02.027. Correspondence: Sikandar Hayat Khan, Department of Pathology, PNS HAFEEZ Hospital, Pathology E-8, Islamabad, Islamabad 44400, Pakistan. E-mail: sik_cpsp@yahoo.com 326 Molecular Therapy: Nucleic Acids Vol. 16 June 2019 ª 2019 The Author(s).