Human genome editing is a method of making precise changes to DNA in human cells. Genome editing tools, such as meganucleases, zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and most notably the CRISPR/Cas9 system, act as molecular scissors that can be programmed to cut out DNA from the human genome, such as harmful genes, or to insert DNA, such as novel genes. The scientific community has rapidly adopted CRISPR/Cas9 because it is a more versatile, precise, efficient, and less expensive genome editing tool. As a side note, the term “genome editing” is used instead of “gene editing” because tools like CRISPR/Cas9 can be used to edit other parts of the genome besides genes.
CRISPR (clustered regularly interspaced short palindromic repeats) is an antiviral component of the bacterial immune defense system. When a virus injects its DNA into a bacterial cell, the bacterial immune system responds by copying parts of the viral DNA and storing it in the bacterial genome, essentially cataloging information on the virus. CRISPR-associated (Cas) enzymes can then reference the viral DNA copy stored in the CRISPR system to identify and break down similar invading viral DNA in the future, and stop the virus before it establishes an infection.
The application of the CRISPR system to human genome editing involves scientists supplying a specific RNA sequence that guides the Cas9 enzyme to cut the DNA at a targeted sequence in the human genome. Scientists can then use this cut to remove DNA or insert a new DNA segment of their choosing. The remarkable power of such genome editing lies in the ability of scientists to select with great precision the stretch of DNA intended for editing. Many diseases and disabilities that afflict humans – such as cancer, cystic fibrosis, and muscular dystrophy – are caused by genomic mutations. CRISPR/Cas9 therapies have great potential to ameliorate some of (and perhaps most of) these conditions through editing out the deleterious mutations.
CRISPR/Cas9 can potentially be used in any organism, including plants, animals and humans. However, this report focused on the human applications of this technology. Important ethical concerns are raised with each translation of CRISPR/Cas9 technology to therapeutics. However, especially salient concerns include the downstream effects of heritable genetic changes from germline (i.e., germ cell) editing of embryos and applications of human genome editing outside of the realm of treating disease or disability, often referred to as enhancement.