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Designer baby

Genetically modified human embryo

  • 28 min read
  • 5 chapters
Diagram of a piece of DNA being removed by tweezers. Modified from two other commons files. Used to illustrate genetic engineering for series template
Ciencias Españolas KoS · CC BY-SA 3.0

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Through Embryo, Fetus and Genetics

This highlights the implications of germline engineering, which involves introducing the desired genetic material into the embryo or parental germ cells. This process is typically prohibited by law, however, regulations vary globally. Editing embryos in this manner can result in genetic changes that are passed down to future generations, raising significant controversy and ethical concerns. While some scientists advocate for its use in treating genetic diseases, others warn that it could lead to misuse for non-medical purposes, such as cosmetic enhancements and modification of human traits.

Pre-implantation genetic diagnosis

Pre-implantation genetic diagnosis (PGD or PIGD) is a procedure in which embryos are screened prior to implantation. The technique is used alongside in vitro fertilisation (IVF) to obtain embryos for evaluation of the genome – alternatively, oocytes can be screened prior to fertilisation. The technique was first used in 1989.

PGD is used primarily to select embryos for implantation in the case of possible genetic defects, allowing identification of mutated or disease-related alleles and selection against them. It is especially useful in embryos from parents where one or both carry a heritable disease. PGD can also be used to select for embryos of a certain sex, most commonly when a disease is more strongly associated with one sex than the other (as is the case for X-linked disorders which are more common in males, such as haemophilia). Infants born with traits selected following PGD are sometimes considered to be designer babies.

One application of PGD is the selection of 'saviour siblings', children who are born to provide a transplant (of an organ or group of cells) to a sibling with a usually life-threatening disease. Saviour siblings are conceived through IVF and then screened using PGD to analyze genetic similarity to the child needing a transplant, to reduce the risk of rejection.

Process

Embryos for PGD are obtained from IVF procedures in which the oocyte is artificially fertilised by sperm. Oocytes from the woman are harvested following controlled ovarian hyperstimulation (COH), which involves fertility treatments to induce production of multiple oocytes. After harvesting the oocytes, they are fertilised in vitro, either during incubation with multiple sperm cells in culture, or via intracytoplasmic sperm injection (ICSI), where sperm is directly injected into the oocyte. The resulting embryos are usually cultured for 3–6 days, allowing them to reach the blastomere or blastocyst stage.

Once embryos reach the desired stage of development, cells are biopsied and genetically screened. The screening procedure varies based on the nature of the disorder being investigated.

Polymerase chain reaction (PCR) is a process in which DNA sequences are amplified to produce many more copies of the same segment, allowing screening of large samples and identification of specific genes. The process is often used when screening for monogenic disorders, such as cystic fibrosis.

Another screening technique, fluorescent in situ hybridisation (FISH) uses fluorescent probes which specifically bind to highly complementary sequences on chromosomes, which can then be identified using fluorescence microscopy. FISH is often used when screening for chromosomal abnormalities such as aneuploidy, making it a useful tool when screening for disorders such as Down syndrome.

Following the screening, embryos with the desired trait (or lacking an undesired trait such as a mutation) are transferred into the mother's uterus, then allowed to develop naturally.

Regulation

PGD regulation is determined by individual countries' governments, with some prohibiting its use entirely, including in Austria, China, and Ireland.

In many countries, PGD is permitted under very stringent conditions for medical use only, as is the case in France, Switzerland, Italy and the United Kingdom. Whilst PGD in Italy and Switzerland is only permitted under certain circumstances, there is no clear set of specifications under which PGD can be carried out, and selection of embryos based on sex is not permitted. In France and the UK, regulations are much more detailed, with dedicated agencies setting out framework for PGD. Selection based on sex is permitted under certain circumstances, and genetic disorders for which PGD is permitted are detailed by the countries' respective agencies.

In contrast, the United States federal law does not regulate PGD, with no dedicated agencies specifying regulatory framework by which healthcare professionals must abide. Elective sex selection is permitted, accounting for around 9% of all PGD cases in the U.S., as is selection for desired conditions such as deafness or dwarfism.

Polygenic risk score (PRS) screening

In the 2020s, companies such as Orchid Bioscience began offering polygenic risk scores (PRS) analysis for embryos during IVF. PRS estimates the likelihood of complex traits, such as height and intelligence, or diseases like diabetes, by summarizing data from thousands of genetic markers. However, many geneticists and bioethicists argue that PRS predictions lack clinical validity and promote eugenic practices that can prioritize socially desirable characteristics. They believe this approach risks reinforcing societal biases that may not be realistic and limits the autonomy and identity of the child as it restricts their life within a framework of genetic predictions. A 2021 study found that PRS explains only 5-10% of variance in educational attainment, highlighting its limited predictive ability.

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