Mitochondrial DNA

Despite the majority of DNA being stored as chromosomes within the nucleus of every cell, there is a fraction of DNA found in mitochondria, known as mitochondrial DNA, or mtDNA. It contains 37 genes which are all involved in allowing the normal functioning of the organelle, with 13 being involved in producing enzymes to carry out oxidative phosphorylation (energy / ATP production) and the remaining 24 carrying instructions for making transfer and ribosomal RNA.

MtDNA is inherited exclusively from the mother, as it is transmitted through the female egg, and will be passed on to both sons and daughters, but only her daughters will be able to continue passing it on. Given that mtDNA is considered nonrecombiant (does not combine with any other DNA), it remains virtually unchanged through the direct maternal line over hundreds and even thousands of generations. Consequently, many people will have almost identical mtDNA, which suggests they share a common maternal ancestor. As a result, mtDNA is almost completely useless when it comes to determining biological parents, as there is no connection between a father’s mtDNA and his offspring’s, and many women have very similar mtDNA, making it almost impossible to distinguish a difference. Only in certain circumstances, such as the offspring having completely different mtDNA to their supposed mother, is it useful in determining biological relations.

Disorders and diseases caused by mutations in mtDNA often affect multiple organ systems, and more specifically have the greatest effects on the organs which require the most energy, e.g. the brain or the heart. One example of  disease caused by mutations is Leigh Syndrome, which is a severe neurological disorder.

Symptoms usually present themselves within the first year of life, although there have been reported cases of patients being in early adulthood before any sign of Leigh syndrome becoming apparent. The first symptoms commonly include vomiting and difficulty swallowing, resulting in stinted growth and issues gaining weight. In addition, movement becomes more and more difficult due to muscle weakness, involuntary muscle contractions, and trouble with maintaining balance. In more advanced cases of Leigh Syndrome, muscle weakness may also affect movement of the eyes, and severe breathing problems which may result in acute respiratory failure. Sufferers of the disease tend to only live for a few years, often dying as a result of respiratory problems.

Whilst the majority of Leigh Syndrome patients inherit it through an autosomal recessive pattern, in which both parents are carriers, around 20% of cases are caused by a mitochondrial pattern. Such cases are inherited from the mother only, and whilst it is not certain that children will inherit the disease, the chances are fairly high. This is the reason that last year, for the first time, a baby was born in Mexico and was declared to be the biological child of three people – two mothers and one father. The technique, pronuclear transfer, with which the embryo was created, aimed to prevent the mother of the child passing on any mitochondrial DNA, to remove the risk of passing on Leigh Syndrome.

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Three parent babies!

This week I was incredibly excited to hear that a second baby with there parents has been born in Ukraine through a complex IVF procedure. The first three part baby was born last year in Mexico to avoid the conceived child suffering from Leigh Syndrome (a severe neurological disorder that causes progressive loss of movement and deterioration of mental functions), which would have eventually proved fatal.

In Mexico, the technique to create the baby involved removing the nucleus from one of the mother’s eggs and inserting it into a donor egg with its own nucleus removed, and this egg was then fertilised with sperm from the father. Mitochondrial DNA from the donor egg is what means the child has three biological parents. However, this was slightly different to the method carried out by the Kiev team in Ukraine, who fertilised the mother’s egg with the father’s sperm, and then transferred the combination of genes into a donor egg.

Originally, the concept of three parent babies was designed to help women who carry mitochondrial diseases have healthy children, but the method was adapted for the couple in Ukraine, who were previously infertile, to enable them to start a family of their own.

Despite this being an incredible medical breakthrough, there is a lot of controversy surrounding this issue; for example, whilst here in the UK there have been three laws passed to allow the creation of babies from three people, UK experts argue that the two procedures that have occurred so far have been highly experimental, and question the ethics of allowing people to create babies in the way.

On one hand, it can be argued that this medical breakthrough is something we should celebrate – it proves just how far we have been able to push the boundaries of science, and it has already allowed us to help two families have a family of their own, something that was previously unthinkable. As well as this, it will enable us to push the field of genetics even further in the future, and could help us to completely remove some genetic conditions, which previously have been untreatable or even fatal.

On the other hand however, given that we have not had the chance to study someone before who has grown up with three biological parents, it is difficult to predict whether the child will be able to live a healthy life – there is always potential for something within their DNA to go wrong. Also, it could lead to complications with guardianship of the child in the future: what happens if the child is orphaned – does the third parent have a duty or a responsibility to care for the child? Moreover, as with the arguments against IVF in general, many religions argue that the creation of an embryo by mechanical means goes against nature, and some believe that to interfere in procreation is to act as God. Furthermore, what about the child themselves – they will grow up knowing that they are part of a scientific experiment, and how will they feel knowing that they have three biological parents? They may even face prejudice at school and later on in life from people arguing that they shouldn’t exist. Finally, whilst we may be able to eradicate some genetic diseases, there is potential that we could create new ones, exposing generations after us to diseases that they would not have suffered from had we not interfered with genetics to begin with.

I hope you have found this enlightening, and if you have any views you would like to share, please leave a comment.

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Cannabis – what’s the problem?

Everyone has heard of the drug cannabis – sometimes more commonly referred to as marijuana, pot, weed or dope – yet whilst anyone could tell me it is illegal in the UK, not many seem to be able to explain why, and so I decided to look into it for myself.

From what I have heard about cannabis in the past, it seems to be the most controversial drug, not because of the effects it has, but because across the world, the laws regarding cannabis are so different. For example, whilst here in the UK, cannabis is considered a class B drug and consequently can result in 5 years in prison for possession, in America, 28 states allow marijuana to be used for medicinal purposes , with 8 of these allowing it for recreational purposes as well. In addition, the majority of countries in South America, and several across Asia allow possession of cannabis provided the person can prove it is for personal use only.

Some people are adamant that cannabis is not harmful in any way, but with the majority of the world’s laws against possession and supplying of the drug, I decided to find out for myself whether what people argue is really true…

In terms of physical health, long term use of cannabis has been linked to the development of multiple types of cancer, including lung, head and even testicular cancers (cannabis is also thought to lower testosterone production levels). Also, it is believed that over a prolonged period of time, cannabis is able to elevate heart rate and blood pressure, meaning it could be an indirect cause of cardiovascular diseases, such as strokes or heart attacks. Furthermore, evidence suggests that cannabis can cause inflammation of the respiratory system, which combined with regular nausea or vomiting is likely to put the person in hospital. Other symptoms include increased hunger, disorientation, slowed reaction times, red eyes and loss of memory.

However, it seems that the physical health symptoms are less of an issue, compared with the mental health problems which appear to affect many more people. Along with a loss of the ability to focus on any one thing for a long period of time, the main risk is of the development of psychosis, and in particular can lead to schizophrenia in some people. As well as this, those who suffer from bipolar or social anxiety disorders are likely to have the symptoms exacerbated by repeated use of cannabis, although the evidence for this is weak. Finally, given that cannabis is considered highly addictive, withdrawal symptoms for those who have become dependant on it not only include fatigue, sleeplessness and fidgeting, but also increased anxiety levels, paranoia and depression.

Despite all this, cannabis also has strong evidence to suggest that it is very helpful in the treatment of some medical conditions, such as benefitting those with glaucoma, controlling epileptic seizures, and in particular the treatment of chronic pain, especially in those with multiple sclerosis. As well as this, it is thought to slow the onset of Alzheimer’s disease, lessens the side effects of treatments for other illnesses (e.g. HEP C treatments) and finally it can massively improve the quality of life for those who suffer from post traumatic stress disorder (PTSD), as it is able to inhibit release of hormones that cause fear and anxiety.

I would argue that the benefits of cannabis to medicine are incredibly advantageous, although I can appreciate why the government is so unwilling to legalise cannabis. Personally, I believe that the drug ought to be able to be licensed to some hospitals in the UK for medical use only, especially given that it is able to provide treatment / relief for such a wide variety of illnesses that are otherwise considered almost untreatable. However, considering the effects on both physical and mental health when the drug is used for purely recreational purposes, I am yet to be convinced that possession of cannabis should be legal for the general public.

I realise that what I have written about remains a very controversial topic, and if you have any comments or additional arguments for or against what I have mentioned then please do let me know.

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The Mesentery – a new organ?

Whilst scanning the news yesterday, one article in particular caught my attention – a new organ has been discovered in the human digestive system!

Previously considered to have been several separate structures that connected the stomach and the intestines, the mesentery has now been reclassified as an organ. This is thanks to the work of Professor J Calvin Coffey, whose research that the connecting region was in fact all one structure; his research suggests that the mesentery secures the small and large intestines in place by connecting them like a belt to the pancreas.


Figure 1: digital representation of the mesentery

Up until now, the mesentery was believed to have one simple function: attaching the intestines to the abdominal wall through the means of a membrane known as the peritoneum, and because of this, it was never considered to have been of much interest, or worth much research.

However, now that the mesentery is officially recognised as an organ, research will be conducted to better our understanding and knowledge of exactly what functions the mesentery performs. This in turn will allow us to recognise areas in which the mesentery could malfunction, enabling us to predict the symptoms of diseases, and consequently allowing for treatments to begin to be developed.

Personally, I find this medical revelation incredibly exciting as it opens the doors to the field of mesenteric science, which, with time, could massively improve our understanding of the not only the mesentery itself, but also the digestive system as a whole. Of course, there is still the need for a great deal of research to be conducted into the function of the mesentery, but in the future, improved understanding could allow us to diagnose and treat previously unknown diseases.

Figure 1

Published: 2017


Access date: 05.01.17