The area of genetics has hit the headlines recently with much excitement and debate around the potential for gene editing to do a variety of things from wiping out malaria and curing cancer to making unicorns.
Rapid advances in our understanding of genetics and the technologies required to analyse our genes have seen increased demand for genetic testing. Whilst some genetic testing is performed in research facilities, many tests are now offered clinically via pathology laboratories.
So what is genetic testing?
First we need to know the basics of what DNA and genes actually are.
DNA is like an instruction manual that tells our bodies how to grow, function and repair. It does this by making all the proteins that perform incredibly important but seemingly mundane tasks that we never think about – like building new heart muscle, or maintaining the microscopic scaffolding that makes up our eyes.
A gene is a small section of DNA that codes for a specific protein. Humans have many genes in common that are identical or very similar. Small differences in some genes are harmless – this is why we see blonde haired and dark haired people. These minor changes drive evolution over many years.
However, some proteins perform functions that are necessary for life. Even the tiniest change in the gene’s coding for these proteins can have disastrous consequences.
Genetic changes are generally caused by changes in the way DNA is copied as a cell divides. If a serious change is present in an egg or sperm at the point when a baby is conceived, it will cause a genetic condition. Cystic Fibrosis and Muscular Dystrophy are examples where essential genes are changed, resulting in malformed proteins that can’t perform vital functions.
Sometimes mistakes in DNA accumulate over time as we age. These can cause cancers. Some changes to DNA don’t directly cause cancer, but can put someone at higher risk of developing cancer for example the genes BRCA1 and 2.
Genetic testing is now used in a wide range of ways, but the most common uses include:
- Newborn screening for genetic conditions such as Cystic Fibrosis
- Genetic testing to diagnose a genetic disorder such as haemochromatosis
- Non-invasive prenatal testing for Down Syndrome
What samples can be tested?
The most commonly used sample is blood, but DNA can also be extracted from
- a biopsy of the tissue you want to examine – such as a tumour biopsy, bone marrow biopsy, or a placental biopsy
- skin cells – hence the cheek swabs used in crime dramas
- hair, and even urine and faeces
What other ways is genetic testing used?
Genetic testing has a number of other uses including:
- helping doctors choose the most effective cancer treatment
- checking organ donor and recipient compatibility
- infectious disease testing – this type of testing is different to those above because rather than examining the patient’s DNA it looks for the DNA of the actual bacteria or virus
- identity testing for criminal investigations (commonly referred to as DNA testing)
- parentage testing
Pathology can discover an enormous amount about a person’s genetic make up – the Catalogue of Genetic Tests and Laboratories contains over a thousand tests. As well as providing information about the individual patient, the results of these tests can help doctors find genetic information that could affect other family members, who may then also have genetic tests performed. Early detection of genetic risk factors can provide a chance for monitoring and preventative measures.