Three-parent families is a topic that particularly interests me due to its relevance now and for the future, allowing women with mitochondrial DNA mutations to have children. This is a topic of ‘personalised medicine’ which is an ever-increasing part of medicine that allows a patient’s treatment to be determined by their genetics. There are ethical issues surrounding personalised medicine due to the fact it is not considered a natural birth so is said to be ‘questioning God’ by the Church of England and encouraging ‘designer babies’ by the House of Lords. Altering nuclear DNA is banned by law in the UK with the exception of mitochondrial replacement.
Genetic medicine is very modern due to its reliance on new technologies such as oligoarrays. An oligoarray analyses nucleic acid transcripts [A Level teaches us that transcription is when DNA is copied into RNA by the enzyme polymerase] to detect micro genetic mutations.
The technology of three-parent families is that the pronucleus of an oocyte (cell which divides by meiosis to form an ovum) from the woman with mitochondrial disease is transferred into a healthy donor cell. Both the mother’s and donor’s oocytes are fertilised by the spermatozoon (motile sperm cell) before the pronucleus is removed from the mother’s oocyte. The pronucleus is removed before the oocytes divide into an embryo. The nucleus contains the majority of genetic content so this will be passed onto the offspring along with normal, healthy mtDNA (the offspring genome is made up of 0.2% mitochondrial DNA). This donor cell with the mother’s nucleus can now divide by mitosis into an embryo. This process of moving the pronucleus from cell to cell is called ‘pronuclear transfer’.
Women need this new technology if they have a mitochondrial disease. Due to the mitochondria being such an important organelle, with the role of synthesising ATP, many organs are affected if the organelle is diseased. Heteroplasmy is when mitochondrial DNA is made up of two types, wild-type and mutant. The severity of symptoms depends on the proportion of mutant mitochondrial DNA per cell. Some problems caused by having mitochondrial disease are blindness, deafness, muscle disease, heart disease, respiratory failure, liver failure and diabetes.
Foetuses are tested by genetic analysis within the first three months (trimester) by examining amniotic fluid or chorionic villus sampling (CVS), or before implanting of an embryo made by in vitro fertilisation called pre-implantation genetic diagnosis, if there is a chance that they may have a genetic disorder.