A fresh pair of genes?

Do genes equal destiny? Anatomically speaking, yes: A child with two X chromosomes will be a girl, and a child with one X and one Y will be a boy. Genes help determine everything from height and hair color to whether a person will enjoy certain flavors. They can also act like mosquitoes and ticks, transmitting disease.

Research on the genome is inspiring ideas for genetics-based treatments. Already, surgeons often send tissue samples from malignant tumors for genetic analysis, so that they can customize a patient’s chemotherapy to target his cancer’s specific genetic mutation. This genetics-inspired technique merely guides treatment: The treatment does not modify a patient’s DNA.

What if a treatment does? That’s gene editing, an attempt to change DNA in living patients. Since all cancers and many other diseases are caused by genetic mutations, successful treatments might lessen much human suffering. We may not know the side effects of a given attempt, but for the kind of dreaded diseases attracting research attention—Huntington’s, muscular dystrophy, sickle cell anemia—a patient might reasonably want to take a chance. Moreover, as with surgery, any benefit or harm is limited to that one patient, who can make an informed decision about whether to proceed.

Much more powerful—and controversial—is heritable gene editing, also called germ line gene editing. These edits would happen at the embryonic stage, meaning that they would affect every cell of a patient’s body and pass to subsequent generations like any gene. The studies of this technique require human embryos, which researchers destroy at the end of each experiment. One source, according to England’s Francis Crick Institute: “Those left over from patients’ fertility treatment and donated by patients. They will be surplus to the patients’ treatment or family-building needs.”

Advocates of caution point out that we do not understand much of the human genome and can’t accurately predict what effect a change would have. Some of what we know from human nature also discourages here: In a Wall Street Journal opinion piece, Marcy Darnovsky of the Center for Genetics and Society argues that “a few advocates of gene editing for reproduction are openly enthusiastic about ‘enhancing’ future generations. … It’s all too easy to imagine fertility clinics offering ‘offspring upgrades’ to affluent parents.”

Science fiction writers have long contemplated such a thing, but life may soon imitate art: CRISPR, a technology used to edit DNA sequences, has become routine for genetic research in mice and other small animals. In 2014, experiments with it led to the birth of twin genetically modified macaque monkeys.

Restrictions on human embryo research are common. Germany’s law, the 1991 Embryonenschutzgesetz (embryo protection law), is among the most stringent, effectively banning any use of human embryos for research. The country’s past shaped its attitude: John Robertson of The University of Texas School of Law wrote in the Columbia Journal of Transnational Law that “revulsion to … the cruel medical experiments that inspired the Nuremberg Code for human experimentation” led to the law. Human genome editing and the creation of human-animal hybrids in Germany both carry penalties of up to five years in jail.

Elsewhere, attitudes are more lenient: In 2015, researchers at China’s Sun Yat-sen University edited the genomes of human embryos with CRISPR. The experiment did not lead to pregnancy, but laid a technical groundwork for future attempts. A second Chinese team published its attempts to engineer embryos’ genomes for HIV resistance in 2016, intensifying debate and leading to calls for a worldwide embargo on embryo research.

As gene editing tools gain power, ethical dilemmas multiply. When, if ever, is it acceptable to use powerful tools with poorly understood effects? As geneticist J. Craig Venter noted in Time, “the techniques have become easier to perform, [but] the ethical issues are not easier.”