The first step is a no-brainer. Say you are one of the tens of thousands of people with Huntington’s disease, a terrible, hereditary neurodegenerative disorder caused by a mutation in the HTT gene. The diseased version of the gene makes an abnormally long protein that becomes toxic in your neurons, eventually killing them. Symptoms usually appear in your 30s or 40s as small twitching movements, a lack of coordination, and depression. In the coming years, the spasms will grow. It will be increasingly difficult to walk, talk, and think. Within 20 years, you will most likely be dead. You are resigned to your fate, but you and your partner would very much like to have kids, and you have no interest in passing this particular legacy to your child.
Today, your best bet is a procedure called preimplantation genetic diagnosis (PGD), in which embryos produced through in vitro fertilization (IVF) are screened for the unwanted gene. PGD has been a game changer for many couples, but it has limitations. You may be one of the unlucky few who has two copies of the bad HTT, in which case all your embryos are guaranteed to inherit one copy. Or you could be uncomfortable with the idea of producing and discarding multiple embryos.
The next step will be screening all those embryos. As part of an IVF procedure, thousands of couples already opt for PGD on their handful of embryos. Combine our increasing ability to read genes with the potential of unlimited eggs, and you get what Stanford bioethicist Henry Greely calls Easy PGD. In his book, The End of Sex, Greely argues that within a few decades, most people in the developed world will reproduce with Easy PGD. A fertility clinic will create 100 embryos for you and sequence the genome of each. You and your partner will then go through the analysis of each potential child, weighing the pros and cons of the musical prodigy with the raised risk of schizophrenia versus the redhead with the strong athletic ability, and decide which of the 100 options to bring into the world.
There will also, of course, be huge quandaries about how Easy PGD could change our understanding of parenthood, families, diversity, and fairness. Will a society that can pick its offspring converge on a sort of Ivy League blandness? Or will daring parents opt for the shar-peis in their prospective litters? What will become of the human race if variance is smoothed out? Perhaps most important, will everyone have access to this technology, or only the well-off? Greely believes Easy PGD will be far cheaper than IVF is today, and likely more of an equalizer than a divider. But at least in the short term, germline editing and Easy PGD may well accentuate the differences in health between rich and poor populations that are already too obvious today.Read More