Three-parent IVF is known as Mitochondrial donation but how does it work?
What are Mitochondria?
Mitochondria are tiny rod-like structures in cells responsible for producing energy (called ATP) that the body needs to function.
Unusually, they have their own DNA, distinct from the genetic material within the cell nucleus.
Mitochondrial DNA (mDNA) makes up about 0.1% of a cell's total DNA and does not affect individual characteristics such as appearance and personality.
What is Mitochondrial Disease?
It is an inherited condition which affects each person differently according to how many cells in the body are affected.
The commonest parts of the body it affects are those which have the highest energy demands - the brain, muscle, liver, heart and kidney.
Sufferers are usually diagnosed when they are children and many have low life expectancies.
Only the more well known Mitochondrial diseases have names. These include Alpers, Leigh’s disease, MELAS and MERRF.
What causes it?
Harmful mutations in mDNA can prevent mitochondria working properly which can then result in a number of diseases.
Some can be serious and life threatening, affect affect major organs and cause conditions ranging from poor vision to diabetes and muscle wasting.
How is it passed on?
Children can only inherit mDNA defects from their mothers.
People with faulty mDNA can develop symptoms or be carriers of the condition without experiencing ill-effects themselves.
What techniques are involved in Mitochondrial Donation?
There are two different procedures - one carried out before fertilisation and the other after.
Maternal Spindle Transfer (MST) involves reconstructing a donor egg, whose mitochondria are healthy, with the mother's DNA before it is fertilised and implanted.
Pronuclear Transfer (PT) is similar but in this case the mother's egg is fertilised first. It's nuclear DNA is then transferred to a fertilised donor egg, containing healthy mitochondria, whose own nuclear DNA has been removed. This healthy fertilised egg is then implanted.
How safe is it?
Animal and laboratory experiments suggest that the procedures are safe, but no-one can say that the risk is zero.
Three separate reviews by an expert panel convened by the Human Fertilisation and Embryology's Authority have found no evidence that the techniques are unsafe for clinical use.
Critics argue that problems might only arise once the procedure is used to create human babies. For instance, replacing mDNA might have more of an impact on personal traits than envisaged.
Unknown epigenetic effects, environmental influences that alter the way genes work, may also have serious consequences for the health of babies, it is claimed.