CRISPR-Cas9 technology is attractive due to its simplicity, specificity, accessibility, economic feasibility, speed, and efficiency. Although scientists predominantly use the technology for gene editing, even individuals without extensive background training in the sciences may access the technology for experimental and recreational purposes. Indefinite and scarce governmental, scientific, and regulatory policies regarding CRISPR enable almost anyone to edit genes with CRISPR. Instructions for performing CRISPR can be found with ease online, including everything from instructions to videos. Even do-it-yourself CRISPR kits – despite the fact that they are unapproved by the Food and Drug Administration (FDA) – are readily accessible and have skyrocketed in popularity.  
However, scientists who work regularly with CRISPR gene editing have identified logistical and safety concerns that have clouded the stratospheric popularity of Crispr-Cas9 technology. These include mosaicism, toxicity, germ line effects, and off-target effects.
Image: CRISPR/Cas9 in Neurons. Credit: T. Macfarlan, National Institute of Child Health and Human Development, NIH. CC BY-NC-CA 2.0.
Although gene editing may seem simple at the cellular level, the practicality and safety of CRISPR in organisms is more complicated. Mosaicism is just one example of this in which genetically-edited cells in an organism have different genotypes (genetic compositions) from one another.  Mosaicism is notable in gene-edited embryos of animals and humans, derived from developmental mutations – in which genetic mistakes such as deletions, insertions, duplications, and translocations occur that may hinder or interfere with DNA replication and recombination. Mosaicism is problematic because that sampling of the genetically modified cells with regarding to the desired gene edits may be highly inconstant, which can have negative implications for biomedical research discoveries.
Toxicity in gene editing is still another problem, as lipid vectors for the delivery of Cas9 and RNA sequences with genetic material to cells can be toxic. 
Another serious problem is the effect of germ line mutations and alterations – gene-editing errors have been known to pass from generation to generation.
Dorkina Myrick, MD, PhD, MPP, is a physician-scientist trained at the National Institutes of Health in Bethesda, Maryland. Dr. Myrick is currently a JD candidate at the Boston University School of Law.
 Maxmen, Amy. “Easy DNA Editing Will Remake the World. Buckle Up.” Wired. August 2015. Online: http://www.wired.com/2015/07/crispr-dna-editing-2/.
 “What are knockout mice?” National Human Genome Research Institute. Online: https://www.genome.gov/12514551. Last Updated August 27, 2015.
 Priti Singh, John C. Schimenti, Ewelina Bolcun-Filas. “A mouse geneticist’s practical guide to CRISPR applications.” Genetics. January 8, 2015 vol. 199 no. 1 1-15. Online: http://genetics.org/content/199/1/1.full.
 David Cyranoski & Sara Reardon. “Chinese scientists genetically modify human embryos.” Nature. Online: http://www.nature.com/news/chinese-scientists-genetically-modify-human-embryos-1.17378.
 Mehravar et al. Mosaicism in CRISPR/Cas-9-Mediated Genome Editing. Developmental Biology. Available online 22 October 2018. Online: https://reader.elsevier.com/reader/sd/pii/S0012160618302513?token=A4F11A8967331D8E6D6DFC733796253792C290F751D2D47B6B08480FB991938C777FB545E618902ADD096143D7A5ABDA. Retrieved 09 January 2019.
 Mosaicism. National Institutes of Health. MedlinePlus. Page last updated: 07 January 2019. Online: https://medlineplus.gov/ency/article/001317.htm. Retrieved 09 January 2019.
 Li et al. CRISPR Established Editor of Human Embryos? Cell Stem Cell 21, September 7, 2017. Retrieved 09 January 2019.
 T.H. Taylor, S.A. Gitlin, J.L. Patrick, J.L. Crain, J.M. Wilson, D.K.Griffin. The origin, mechanisms, incidence and clinical consequences of chromosomal mosaicism in humans
Hum. Reprod. Update, 20 (2014), pp. 571-581
 Lamphier et al. Don’t Edit the Human Germ Line. Nature. 12 March 2015. http://www.nature.com/news/don-t-edit-the-human-germ-line-1.17111.
 Image: CRISPR/Cas9 in Neurons. Credit: T. Macfarlan, National Institute of Child Health and Human Development, NIH. CC BY-NC-CA 2.0. Description: “CRISPR/Cas9 engineering was used in mouse embryonic stem cells to insert a GFP tag in frame with the motor-neuron-specific transcription factor HB9. These cells were differentiated into motor neurons. The resulting motor neuron nuclei are labeled with the GFP reporter (green) and counterstained with antibodies against the neuronal marker Tuj1 (red).” Online: https://www.flickr.com/photos/nihgov/36473308551/in/photolist-E9oz5H-xVEjQo-Dn2dTM-HorP37-Gw18sX-HorP3Y-GAACEb-FupitL-GTgDQ6-QZkrnM-2dmWECP-KRaVP5-25MGXLD-25jKZNF-23QQGCE-GsAwtj-24AjetM-24mtzLM-21ZupSc-21ixQhp-YtztKe-Hor2zd-HKQJZm-HE9yAS-HKMNH9-Xz2eVr-VYphcA-W7bb3o-VmuRU1-TQnXCY-RPbhgU-QDV4Jp-RnxWxQ-NLFs4u-MEbLzY-L6gJRE-L4rKdf-KhaJe4-L4rKeN-JjdhSU-D3e3kb-DaUeBN