In vitro fertilization (IVF) is a technology involving fertilization of an egg by a sperm cell outside the body in a laboratory dish. The origin of the term in vitro, which literally means in glass, dates back to the era when glass containers such as test tubes or petri dishes were popular for cultivating tissues outside the living organism it originated from. In recent times, when plastic has replaced glass, the term in vitro refers to any biological procedure that is performed outside the living organism to distinguish it from an in vivo procedure, where the tissue remains inside the living organism in its native environment (1).
Babies conceived as the result of IVF are often called “test tube babies”, which refers to the tube-shaped containers of glass or plastic called test tubes that are commonly used in biomedical laboratories. The first successful birth of a “test tube baby”, Louise Brown, occurred in 1978. Robert G. Edwards, the physiologist who pioneered the technique, was awarded the Nobel Prize in Physiology or Medicine in 2010 (2).
In addition to inheriting the full complement of nuclear DNA from the donor mother and father, the IVF embryo inherits mitochondrial DNA exclusively from the mother. The mitochondria, which are the powerhouses of cells, have their own DNA, which is passed down directly by the mother to the offspring, thereby increasing the risk of transferring mutations in the mitochondrial DNA. Defects in the mitochondrial DNA have been linked to blindness, heart failure and muscular and cognitive problems (3).
In an attempt to minimize the risk of transferring mitochondrial defects to successive generations researchers have developed a new technology known as mitochondrial DNA replacement therapy. This involves taking the nucleus of a fertilized egg from a mother carrying the faulty mitochondrial DNA and transplanting it into a healthy donor egg that has had its nucleus removed. The new embryo will contain nuclear DNA from the intended father and mother, as well as healthy mitochondrial DNA from the donor egg, effectively creating a “three-parent” baby. Although the donor egg is said to contribute only 0.1% to the genetic make -up of the child, when examining the genetic material of these children there are still 3 identifiable genetic parents (4).
Mitochondrial defects are associated with many rare and often serious metabolic diseases as well as more common, chronic illnesses and are typically diagnosed in childhood; as many as 1 in 4,000 children may be affected, but they can occur at any age (5, 6). Although mitochondrial diseases can be the result of complex inheritance patterns from the mother and the father, actual defects within the Mitochondrial DNA itself are inherited only from the mother; so transferring nuclei from eggs containing defective mitochondria to eggs from healthy mothers will help mitigate the risk of passing on such mitochondrial DNA defects to the offspring (5).
- In vitro fertilisation. Wikipedia. [Internet: http://en.wikipedia.org/wiki/In_vitro_fertilisation (Accessed 3/6/2014)]
- Medical News Today. (2013) What is In Vitro Fertilisation? What are Test Tube Babies? [Internet: http://www.medicalnewstoday.com/articles/262798.php (Accessed 3/6/2014)]
- United Mitochondrial Disease Foundation. What is Mitochondrial Disease? [Internet: http://www.umdf.org/site/c.8qKOJ0MvF7LUG/b.7934627/k.3711/What_is_Mitochondrial_Disease.htm (Accessed 3/6/2014)]
- Amato, P. et al. (2014) Three-parent in vitro fertilization: gene replacement for the prevention of inherited mitochondrial diseases. Fertil. Steril. 101, 31–5.
- Cyranoski, D. (2012) DNA-swap technology almost ready for fertility clinic.
- Cleveland Clinic. (2010) Myths and Facts About Mitochondrial Diseases. [Internet: http://my.clevelandclinic.org/disorders/mitochondrial_disease/hic_myths_and_facts_about_mitochondrial_diseases.aspx (Accessed 3/6/2014)