News broke on Tuesday (Sept 27) of the birth of a baby in Mexico who was conceived with a new medical technique that uses the DNA of three parents in the embryo. The Straits Times helps explain the process and what this development means for human reproduction.
1. What are the puzzle pieces in play?
Genetic material of every living being is encoded on the strands of deoxyribonucleic acid (DNA) in the nucleus of the cell. The nucleus, like the other organelles, floats in the jelly-like cytoplasm inside the cell.
In addition to the nucleus, human cells also contain mitochondria, which provide the cell with energy. The endosymbiotic theory suggests that mitochondria used to be single-celled organisms that were incorporated into human cells, in the early age of cellular life, billions of years ago. Therefore, mitochondria also contain DNA, known as mitochondrial DNA (mtDNA).
mtDNA is inherited almost exclusively from the female parent. Unlike nuclear DNA, mtDNA does not control the appearance or genetic make-up of a person.
2. How does the new reproductive technique work?
Typically, assisted reproduction involves using sperm to fertilise an egg in a laboratory. It is known as "in vitro" fertilisation - "vitro" referring in Latin to the "glass" of a Petri dish or a test tube - as opposed to "in vivo" fertilisation, which takes place inside the body.
Several embryos are developed in this way and one or more of the embryos are then implanted into the mother's uterus.
The newest "three-parent technique", called spindle nuclear transfer, involves two eggs - one from the mother, and one from a donor.
Both eggs have their nuclei removed, and the nucleus from the mother's egg is inserted into the donor egg. This egg, which can be fertilised with the father's sperm, holds the mother's nuclear DNA and the donor's mtDNA.
3. What other similar methods exist in this brave new world?
Pronuclear transfer was given the green light in the United Kingdom last year. This technique involves fertilising both the egg of a mother with faulty mitochondria, and a donor egg with healthy mitochondria.
The nuclear material of both eggs are extracted at an early stage, before the fertilised eggs develop into embryos. The chromosomes containing the parents' DNA are then implanted into the donor egg.
A previous three-parent technique used cytoplasmic transfer to treat infertility. The cytoplasm from a donor would be introduced into the mother's egg, with some mitochondria - and mtDNA - coming along for the ride.
Preliminary studies with mice also suggest that it could eventually be possible to develop embryos using the genetic material from two eggs or two sperm, which would be a boon for same-sex couples who want genetically related children.
4. Why would people object?
The couple who successfully underwent spindle nuclear transfer this year decided against using pronuclear transfer because it involved discarding fertilised eggs. They felt that this did not accord with their Muslim faith.
Some religious people have qualms about assisted reproductive techniques because they believe that a fertilised egg constitutes a distinct human life, and consider the discarding or destruction of embryos in the process to be unacceptable. Some also believe that conception should take place only during natural sexual relations between a married couple.
Earlier attempts at using three-parent techniques to treat infertility or genetic disorders in the 1990s were called off for medical reasons, when miscarriages or developmental disabilities arose.
The scientific community was also concerned that the unusual genetic code of a female child with three parents' DNA could be passed down to her own children and subsequent generations.
5. Is this technique legal?
Three-parent techniques have been off the table in the United States since 2002, due to safety and ethical concerns by the Food and Drug Administration.
In 2015, the United Kingdom became the first country to legalise pronuclear transfer.