Michael Phelps won his 23rd gold medal in the Rio Olympics last week, and Katie Ledecky broke world records in multiple events, leaving the rest of the world’s greatest swimmers in her wake.
The success of the world’s elite athletes is not only due to drive, determination, practice and persistence, but also to physical traits that allow them to crush their competition. Height, muscle mass, joint flexibility and other genetic traits have all been mentioned in media coverage of Michael Phelps’s world domination of swimming.
As a fertility specialist, I talk about genetics every day with my patients. The ability to screen embryos for genetic defects has been around for over 20 years, but the use of genetic screening in IVF has multiplied astronomically in the last few years due to advancements in technology and a decrease in cost. With an increase in use, there is an increase in misconceptions about what we can do with genetics in 2016. Every day, I answer questions like these:
“Can we clone Michael Phelps?”
No, we’re not there yet. Twenty years ago, news broke that a sheep named Dolly had been cloned, and she’s been brought up with each new advancement in cloning technology ever since. Cloning basically means creating genetically identical offspring by replacing the DNA (genetic code) from an egg with the DNA from an adult cell so that the developing embryo will have the genetics of the adult rather than that of the original egg.
Dolly was not a complete genetic replica (only the nuclear DNA was replicated, not the mitochondrial DNA), and she had some health issues (she died young with signs of old age, earlier than expected). With the advancements in stem cell technology and other genetic techniques, it’s only a matter of time and science before we can clone Olympic athletes, but we are not there yet, and the ethical controversies surrounding this idea are mind-numbing.
“Can I choose the gender of my baby?”
Yes, but only in the lab. While there are many theories on timing intercourse, positions and foods in an effort to influence gender, and there have been attempts at sorting sperm based on gender, the only definitive way to select for gender is to test embryos (after fertilization).
This process requires in vitro fertilization – egg extraction, fertilization with sperm, biopsy of cells away from the developing embryo, and testing those cells for X and Y chromosomes. So ‘Yes,’ you can choose the gender of your baby, but it’s complicated, expensive and ethically challenging.
“Can genetic screening of embryos prevent birth defects?”
Yes and no. Genetic testing is a broad term, and birth defects are complicated. Patients who know they are carriers for genetic defects that lead to specific diseases like cystic fibrosis can screen their embryos to prevent passing these diseases on to their children in a process commonly referred to as preimplantation genetic diagnosis.
The majority of genetic testing of embryos in IVF clinics today, however, is looking for a balance of chromosomes in a process called preimplantation genetic screening or chromosomal screening. Each embryo should have 23 chromosome pairs (stacks of genes), and each pair should have one chromosome copy from the egg and one copy from the sperm.
Embryos with chromosome imbalances have a lower chance of implanting and a higher chance of miscarrying, so screening embryos for a balance of chromosomes can improve success and efficiency of IVF treatment. Birth defects are multifactorial and complex, and genetic screening of embryos should not be a substitution for recommended prenatal testing like ultrasounds and amniocentesis.
“If I use donor egg, then the baby is not my baby, right?”
It’s actually more complicated than you’d think. When a woman carries an embryo created from a donor egg, she can influence which genes are expressed in the offspring. This concept, called epigenetics, involves the assumption that what surrounds the genes or DNA influences their role in development. The concept that the prenatal environment (gestational mother) will impact which genes get expressed in the developing embryo – no matter who the genetic parents are – can be comforting to women feeling nervous about a lack of connection to a child originating from a donor egg. Regardless of genetics, the mother raising the child is a mother.
“Can you give me a designer baby?”
No. We cannot select embryos for hair color, eye color, intelligence or athletic ability. I often tell patients, “We’re not in Gattaca yet.” In Gattaca, the 1997 feature film set in the future starring Ethan Hawke, Jude Law and Uma Thurman, people who can conceive naturally choose to conceive with IVF in order to genetically engineer their children for superior traits. It’s a highly entertaining movie, but as the movie demonstrates, it may be best to keep this idea fiction for as long as we can.