Is the only way to eradicate Mitochondrial Disease through three parent babies?
Mitochondrial disease is a chromosomal disease that can be either a recessive or dominant gene that is passed down through the mother’s mitochondria. This disease can be fatal and there is currently no cure. So, what is mitochondrial disease and how could three-parent babies eradicate it?
Mitochondrial disease is an inherited chronic illness that can be present at birth or develop later in life. It causes devastating physical, mental, and cognitive disabilities with symptoms that can include loss of muscle coordination, poor growth, seizures, vision and/or hearing loss, muscle weakness and pain, gastrointestinal issues, learning disabilities, and organ failure (AMDF, 2017).Mitochondria are the powerhouses of our cells providing the body with over 90% of the energy it needs to sustain life (Sample, 2015). When the mitochondria are not working properly, cells begin to die until eventually whole organ systems fail and the affected person’s life is in danger (AMDF, 2017). Mitochondrial diseases tend to strike in childhood and get worse over time. They often prove fatal before adulthood. The parts of the body that need the most energy are affected the worst: the brain, muscles, heart and liver (Sample, 2015). Faulty mitochondria have been linked to more common medical problems, including Parkinson’s, deafness, failing eyesight, epilepsy and diabetes (Zoloth, 2015 ). Only mothers pass on their mitochondria to their children because the fathers mitochondria gets destroyed during the fertilisation of the egg (see figure 1). If these faulty mitochondria are a recessive gene trait, often no other family members appear to be affected. There is a 25 percent chance of the trait occurring in other siblings (Oxford, 2011). If this gene trait is dominant, the disease often occurs in other family members. In this case there is a 50 percent chance of the trait occurring in other siblings (Oxford, 2011). Around 1 in 200 children are affected by mitochondrial disease. One in 6,500 have serious illnesses that can cut their lives short (Sample, 2015). It is estimated that 1 in 4,000 people have the disease. However, a new technique has been discovered that can prevent babies from being born with the disease.
Figure 1: Diagram showing fathers mitochondria being destroyed in the fertilisation process. (Smith, 2015)
Scientists have developed two techniques to stop mitochondrial diseases being passed from mother to their child. The technique makes use of the fact that the main DNA blueprint is nicely packaged up in the nucleus that is stored in the cytoplasm. The first is called mitochondrial spindle transfer (MST) (Sample, 2015). In this, standard IVF procedures are used to collect eggs from the mother with the faulty mitochondria. The nucleus is taken from one of the eggs that was collected and drop it into a healthy donor egg that has had its own nucleus removed. The reconstructed egg contains all the ‘normal’ genes from the mother, but her faulty mitochondria are replaced by those from the healthy donor. The egg is then fertilised with the father’s sperm. The second procedure is called pronuclear transfer (Zoloth, 2015 ). It is similar to MST, but both the mother’s and donor’s eggs are fertilised first with the father’s sperm. Before the eggs divide into early stage embryos, the parents’ chromosomes are removed from the mother’s fertilised egg and placed into the donor egg, which has had its own chromosomes removed (Sample, 2015). The resulting embryo has the usual 23 pairs of chromosomes that hold the mother and father’s DNA, but the 37 mitochondrial genes, about 0.2% of the total, come from a third person, the donor. (Fraizer, 2006).
Figure 2: A diagram of the two transfer procedures described in the above paragraph (Sample, 2015)
Both procedures have been tested in animals and resulted in healthy offspring. Good results have also been seen in human cells, but treated embryos have not yet been implanted into a woman to achieve a pregnancy. HFEA’s independent scientific panel concluded there was no evidence the procedures were unsafe (Zoloth, 2015 ). If couples are trying for a baby with healthy mitochondria, these treatments are very achievable way for them to have children biologically connected to them. However, before this procedure was discovered couples would have to have children differently.
Defects of the mitochondrial genome take the form of point mutations and deletions, and many hundreds of different mutations associated with disease have been described().These mitochondrial mutations may be either homoplasmic, in which all copies are mutated, or heteroplasmic, with a mixture of mutated and wild-type mitochondrial DNA present. The majority of mitochondrial DNA mutations described are heteroplasmic and the more mutated DNA the more severe the symptoms of the disease is. Mitochondria take in sugars and proteins from the food we eat and produce energy called ATP that our bodies use to function properly. In primary Mitochondrial disease, protein that is directly used by our mitochondria is mutated and in secondary Mitochondrial disease, the mutation is in protein that is not directly involved in energy production (). Every organ in the body needs functioning mitochondria to perform the actions necessary for a healthy life. The exact genetic mutations determine which form of mitochondrial disease is present and which organs are affected(). There are hundreds of different mitochondrial diseases and among individuals with similar genetic mutations, there is such a diverse spectrum of symptoms. It is a common that individuals with the same mutation may not have the same disease. Because of the extensive number of possible mutations that can cause mitochondrial disease, diagnosis has been difficult. Genetic testing is time consuming and costly and might not identify the correct mutation. With the development of next-generation sequencing (NGS), a genetic testing process that allows a person’s entire genome to be sequenced in one day, it has become much easier to identify specific mutations and to identify the best treatment options ().
Where there are other options for couples struggling with the burden of faulty mitochondria, three parent babies are the best option for future generations to be born with heathy mitochondria. With three-parent babies couples can have children genetically theirs with no need to even thinking about aborting their pregnancies. Options like adoption or IVF do not solve the problem of the women who carries the faulty mitochondria, it does not eradicate the disease. Treatment does not eradicate the disease either it merely attempts to soften the impact of the symptoms. There is a chance that the disease could arise again in future generations. The only real way to eradicate this disease is to ensure people who have the affected alleles do not have children but that is not a reliable option. This three parent baby procedure has been developed and it seems to be the only way to effectively eradicate the disease.