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The science of genetics is developing at breakneck speed. So much so, there are tests we can now undertake on DNA without even knowing what they mean. Many of these tests are being offered by private laboratories and clinics without a full explanation of the implications. This leaves many patients with questions that cannot be answered. We will cover specific genetic illnesses in future articles, but this is our guide to the basics of private DNA testing.
What is DNA?
DNA is the blueprint for life. It is a string of molecules, the components of which form a code used to put building blocks in the right order to make the proteins that are essential for life. It is arranged in long strips called chromosomes. A gene refers to a specific section of a chromosome that codes for an individual protein. There are approximately 25000 genes spread across the 46 chromosomes that exist in nearly every type of human cell. A staggeringly low number considering worms have 20000 genes.
What is a genetic disease?
Special machines inside each cell read DNA and build the proteins that let you live. Tiny variations (also called mutations) in the DNA code can lead to changes in a protein that can alter its function. The 46 chromosomes in human cells contain 6 billion items of information and just one change in that 6 billion long sequence can cause a gene to produce a faulty protein. For example, in Cystic Fibrosis, there is one mutation in the DNA sequence that codes for a protein which controls the movement of fluid across a cell wall. This means, in people with the faulty gene, cells in the body where mucus is produced do not function properly and produce thick, sticky mucus. This clogs up the lungs causing breathing difficulties and an inability to fight infection and also stops the pancreas from function properly leading to difficulty in digesting food, malnutrition and poor growth.
Different types of genetic disease.
The most important thing to remember is that not all genetic diseases are inherited. Some mutations are inherited from your parents, others are known as sporadic and are caused by damage to your own DNA from a variety of insults such as infection, chemicals or radiation.
Cancer is an example of a disease cause by both inherited and sporadic mutations. Most cancers are caused by a sequence of mutations which damage the genes that control replication of cells. The full sequence is needed to do the damage which allows cells to replicate unchecked and grow locally as well as spread round the body. Some people inherit a mutation which gives them an unfortunate head start in the sequence of mutations needed to cause cancer. Those affected are more likely to develop cancer and at an earlier age where those without need more mutations to cause the damage and are therefore less likely to get the disease and tend to be older if they do.
What causes damage to DNA?
We know that infection, chemicals and radiation can cause DNA damage. For example, repeated exposure to sunlight, a form of radiation, damages the DNA inside skin cells causing them to replicate uncontrollably and spread. Chemicals in cigarette smoke damage the DNA in lung cells. The more you expose yourself to these things the higher your chance of cancer.
But DNA can also be altered by mistake. Cells divide all the time to produce new cells. This is a common process occurring in your body all the time. Before a cell divides it must first create another copy of its DNA before splitting itself into 2. The protein that replicates the DNA sometimes gets it wrong, about once in every 100 million pieces of code it reads. The cell is clever enough to have a checking mechanism and can repair the mistake but this is not always effective. Often the mistake is of no consequence. Other times the mistake has devastating effects on the function of proteins that will be built from the altered DNA causing a myriad of illnesses. Of course change can also be good and it is good changes giving us better functions which, over billions of years have allowed us to evolve from single cell organisms into the complex machines we are today.
What else do we know about genes?
In the early part of this century, the full sequence of DNA from one human being (known as a genome) was mapped in it’s entirety. This was a huge undertaking which took more than a decade and cost $3bn and was a landmark for genetics research. Technology is advancing at such a pace that you can now have your own genome mapped in a day for a few thousand pounds. Within a few years it will be done in a few minutes for a few pounds. At present, the vast majority of this information is completely useless to us. Like landing on the moon, developing the process has led to lots of new discoveries but much of what we hope can be achieved by getting there is science fiction rather than science fact. This is not to say it has been a pointless endeavour, far from it. Unlike the moon, we continue to explore the human genome on a daily basis and get closer to developing cures for the devastating illnesses that occur from errant DNA. What largely escapes us is therapeutic interventions that give us the ability to replace faulty DNA and reverse the pathological processes that have occurred. That is the holy grail of genetic research.
What is genetic testing?
Although there is much we don’t know, there is a great deal that we do know and can put to good use. We know the specific gene that causes many illnesses and it’s exact location on a chromosome. We know the exact mutation out of a possible 6 billion in many thousands of different diseases. Testing genes falls into 2 broad categories- looking for diseases an individual already has, and looking for ones they may develop in future. Testing for known disease is critical for the diagnosis and treatment of many diseases but testing for future disease raises a number of ethical and moral issues which are as yet unresolved.
Testing for known disease.
This itself splits into a few categories.
Some diseases need 2 copies of a faulty gene, one from each parent, for the illness to manifest itself. If a person who is unaffected but carries 1 faulty gene has a child with someone else with a faulty gene then both parents will be perfectly well but their children will have a 1 in 4 chance of having 2 faulty genes and being affected by the illness, a 2 in 4 chance of being a carrier, and a 1 in 4 chance of having 2 normal genes. It is, of course, understandable that those affected by these genes will want to have unaffected children and the ability has existed for quite some time to test foetuses for their carrier status although the parents are then faced with the choice of proceeding with an affected pregnancy or having a termination. Fortunately the ability now exists to test embryos at the earliest stage of IVF and only implant embryos which are unaffected. the process is however very expensive and only available in a few centres worldwide.
Other genetic illnesses only need one copy of a faulty gene to cause symptoms. A thankfully rare example is Huntington’sDiseasewhich it is possible to test for. The downside of testing is that the condition is untreatable and many affected commit suicide rather than live to develop a debilitating neurological disease. For others illnesses though, the effects are less severe and testing at birth or prenatally is essential for confirmation of diagnosis and planning early treatment that can improve outcomes dramatically.
Other uses of genetic testing include forensic analysis, genealogical and paternity testing.
Testing for unknown disease
Also known as Predictive Testing or Predictive Medicine, this is a very controversial area. It uses knowledge which in many cases is not yet fully verified to predict the risk of an individual developing a genetic disease such as Alzheimer’s or some types of cancer. The main difficulty is that the mechanisms by which these diseases develop are not fully known and no degree of certainty can be given. It is likely that they involve multiple mutations of which you may have inherited only one. All the tests will tell you is that you are more likely to develop an illness than average. They will not, and are unlikely to be able any time soon, tell if you are definitely going to be affected. Laws have had to be implemented to stop insurance companies using this information to underwrite any form of health or life insurance policies. Many argue of the futility of knowing that you may develop an untreatable disease. There is however significant demand for these tests and the best we can hope is that they will become more sensitive and useful in coming years. In the meantime you must be wary of undertaking predictive testing and carefully scrutinise the claims being made by the myriad of companies seeking to profit from offering these services.
Why is some testing not provided by the NHS?
Predictive testing is largely offered by commercial enterprises who may not have such rigorous procedures and contamination or errors may be more common. They also have no proven clinical benefit as no treatment is possible.
Paternity testing is not something the taxpayer would expect to fund in any country.
Genetics is an extremely complicated subject both scientifically and ethically and this article aims only to inform and give a background of information. If you have any questions your first contact should be your GP. Many genetic problems are treated within the NHS but most geneticists will also offer the facility for private consultations. Due to the complexity of genetics, the speed at which it is evolving and the psychological impact of the test results we would not recommend undertaking any form of private DNA testing without the advice of a specialist.
The information in this article is intended as a guide and is not a replacement for medical advice. If you have any doubt you should always speak with your own doctor. If you wish anything clarified please leave a comment in the box below. Although at times we may discuss private medical insurance (also known as private health insurance, healthcare insurance or health care insurance) we do not offer financial advice and recommend you seek the services of an FSA registered broker before purchasing any form of insurance. We do not accept responsibility for the accuracy of content provided by external sources such as guest bloggers.