Article Jul 9, 2015

Explainer: What you should know about genetic modification of humans

Several months ago a team of Chinese scientists sparked a worldwide ethical debate after reporting their experiments using germline editing on the genomes of human embryos. Here is what you should know about what has been called “genetics new battleground.”

What is a genome?

A genome is an organism’s complete set of DNA, including all of its genes. Each genome contains all of the information needed to build and maintain that organism. In humans, a copy of the entire genome—more than 3 billion DNA base pairs—is contained in all cells that have a nucleus.

What is a human germline?

Our genes, the basic physical and functional unit of heredity, are passed on from generation to generation through our sex cells (i.e., ovum (egg) and sperm). These sex cells are part of the germline. The term germline can refer to these cells in an individual or to the lineage of cells spanning generations of individuals. The other cells in the body that are not part of the germ line (and hence do not pass on traits to other generations of people) are called somatic cells.

What is germline editing?

Gene editing (or genome editing) is a form of genome engineering in which DNA is inserted, replaced, or removed from the genetic material of a cell using artificially engineered enzymes, or "molecular scissors." Germline editing is when this procedure is used on the genome of germline cells.

How is genome editing done?

A common method of genome editing, and the process used by the Chinese researchers, is the CRISPR/Cas9 system. The simplistic explanation is that the “molecular scissors” (Cas9, an RNA-guided DNA enzyme) cuts an enzyme on a specific spot of DNA in the nucleus of a cell. The cell then repairs the break using a piece of single-stranded DNA that has been injected into the cell by scientists.

The following video provides a more in-depth, technical explanation of how CRISPR and Cas9 edit genes.


What is gene editing used for?

The CRISPR/Cas9 method has been used for such purposes as to fix defective DNA in mice, curing them of genetic disorders, and to edit genes in crop plants to improve and increase food production. In theory, the process may one day be used to cure genetic diseases in humans such as HIV/AIDS, hemophilia, and sickle-cell anemia.

What did the Chinese researchers do?

A team of Chinese scientists at Sun Yat-sen University in Guangzhou obtained non-viable embryos (i.e., those which cannot result in a live birth) from local fertility clinics. The team attempted to modify the gene responsible for a potentially fatal blood disorder using the CRISPR/Cas9 method on the genome of the embryos. The researchers, who published in the online journal Protein & Cell, say that their results reveal serious obstacles to using the method in medical applications. According to Nature News,

The team injected 86 embryos and then waited 48 hours, enough time for the CRISPR/Cas9 system and the molecules that replace the missing DNA to act — and for the embryos to grow to about eight cells each. Of the 71 embryos that survived, 54 were genetically tested. This revealed that just 28 were successfully spliced, and that only a fraction of those contained the replacement genetic material. “If you want to do it in normal embryos, you need to be close to 100%,” Huang says. “That’s why we stopped. We still think it’s too immature.”

Is gene editing unethical?

The main ethical consideration for gene editing is the purpose (i.e., therapeutic or enhancement) and long-term impact. This is why the ethical issues differ for gene editing on somatic (non-reproductive) cells (which would affect only the individual being treated) and on germline (reproductive) cells (which could potentially impact not only the individual but their offspring and future generations of their descendants).

The concern for germline editing is that therapeutic treatments that are passed along to future generations may have unexpected and unintended consequences. In essence, we would be experimenting on future generations without their consent.

The other worry is that the procedure could eventually be adopted for non-therapeutic genetic enhancement, a form of eugenics. The process could be used by wealthy people to create “designer children” whose genetic “improvements” (e.g., height, intelligence, longevity,  would be passed along to future generations.

Is there an ethical consensus on germline editing?

Currently, most researchers and ethicists agree that genome editing of human somatic cells for therapeutic treatments is largely uncontroversial, while germline editing should be prohibited. While the White House currently opposes human germline editing, the United States has not officially banned the procedure. The process is banned, however, in 15 of 22 nations in Europe.

One area of disagreement is between groups who think that all forms of germline editing should be disallowed and those who believe the process should be used for research purposes on non-viable germline cells.

Why is non-therapeutic genetic enhancement problematic?

From a Christian perspective, therapy implies fixing a malady that is a result of sin entering the world, such as curing diseases or restoring broken physical systems. Enhancement, in contrast, is attempting to make improvements of the body that are either not the result of sin or not necessarily caused by human brokenness. Distinguishing between therapy and enhancement is a perennially tricky issue for Christian ethicists. Additionally, not all therapy is beneficial and not all enhancements are sinful.

Using gene editing for enhancement, though, is troubling for several reasons. For example, using the process on ourselves implies that humans know how to “improve” on God’s general design for the human body. It also can imply that certain traits (such as height or a particular IQ) are so preferable that they should be purposefully engineered so that they can be distributed in a way that is outside the normal distribution range for the human species.

Other concerns include questions about the cultural and social impacts of having certain humans be engineered to have the “right” traits. Will the changes lead to unjust forms of inequality? Will those who do not possess the preferred traits be treated as inferior or sub-human? Will discrimination increase for those who are unable or unwilling to modify their children?

Ultimately, the reason we should oppose germline editing is because children (and future generations of children) are to be considered as gift from God (Psalm 127:3) and not as products that we can tinker with and modify to our preferences.