Saturday, December 16, 2017

Understanding genetics

 Human Genetics Research is a hot topic these days as Trinidad and Tobago prepares to launch its first large-scale human genetics research project. Unfortunately, much of the discussion uses technical language that is incomprehensible to most of us. In a recent interview, human geneticist Dr Allana Roach sought to give a basic understanding of human genetics.

What is human genetics and what are genes?

Simply put, human genetics is the study of inheritance in humans. You’ve probably heard people say “You’ve got your father’s nose” or “Cancer runs in my family.” Human genetics aims to explain how these traits pass from generation to generation.

If you could peer into any one the 50 trillion cells in your body, you’d find a complex and busy world, with a centre called a nucleus. The nucleus contains 23 pairs of molecules called chromosomes. One chromosome in each pair comes from your mother and the other from your father. Together, these chromosomes contain the set of instructions or the blueprint for making you. 

A gene is a small section of chromosome that contains instructions that determine “something” about you. Each gene determines an aspect of who or what you are and how everything works on the inside. Humans have roughly 23,000 genes and each cell in your body carries its own copy of all of them. 

If each cell carries the same 23,000 genes then why is my eye different to my elbow?

Genes are called the “blueprint for life” because they tell each cell what to do and when to do it. However, whilst each cell contains the same blueprint, there is a complex system of genetic switches that turn genes on and off, making sure the right instructions are carried out at the right time in the right cell. Genetic switches determine everything, including the development of your eye and your elbow. It also explains why you digest food in your stomach and not in your eye. (A little genetics humour!) 

So if each person carries the same 23,000 genes, then why are we different?

We are different because there are variations in our genes. The first level of variation results because we randomly obtain each of the two copies of our genes from our parents, who got their two copies from their parents, and so on. Additionally, most of our characteristics are determined by more than one gene or as we say in “genetics speak” most “phenotypes” (characteristics) are “polygenic” (caused by many genes).  Finally, the same gene is may be expressed differently in different environments. 

So explain variations in genes and why they are so important?

Genes change over time. As we grow and develop, new cells are made and the genetic information is copied so each new cell has its own set of instructions. This copying is not 100 per cent perfect so variations or “mutations” occur. If mutations occur in sperm or egg cells, they may be passed from one generation to another. Some mutations can be beneficial, keeping populations healthy. Many mutations are silent, having no effect. And a few can lead to disease, for example sickle cell disease, a disorder caused by the mutation of a single gene; or breast cancer which usually results from a series of mutations.  

Are there tests available to check for variations in my genes that may lead to disease?

Yes. Genetic tests are available to check for variations in several genes that have been linked to disease.  Genetic testing can be performed on foetuses to check for the presence of an inherited genetic disease; to match organ donors and recipients; to establish paternity or maternity, or to investigate evidence from crime scenes. However, most tests are not widely available or cost-effective enough to include in the routine diagnosis of most diseases.

What is the goal of health-related genetics research? 

The goal of health-related genetics research is to identify changes in our genes which will aid in our understanding of human health, the characterisation of disease and the development of technologies to improve the treatment and prevention of disease. 

If the goal of health-related genetics research is so good, then why is it often shrouded in controversy?

How much time do we have? The controversy is extremely complex, but I will try to summarise a few main points. 

For some it’s a moral issue. Many believe that genes hold the key to our existence and any manipulation or inquiry into genes is meddling with God’s work. 

Another issue is lack of understanding about the conclusions that can be drawn from the human genetics research. Some mistakenly believe that it is as easy as “show me your genes and I’ll show you who you are,” but truthfully, we don’t know what some variations mean or their effect on human health.

Finally, a far greater challenge is the human condition. History has proven that any technology developed by human kind can be used to do just as much bad as good. The technology and information that can be gained from human genetics is no different. 

Does this mean we should not pursue human genetics research?

Not at all! It means that human genetics research must be governed by STRICT codes of ethics. Like all other research involving humans, it must undergo stringent scrutiny and approval processes before it can be conducted. Nothing in life is fool-proof but internationally, and right here in T&T, there has been immense progress to ensure the ethical and responsible conduct of human genetics research.

Food for Thought

Your genes are not your fate! Genes are not a blueprint in the same way an architectural blueprint determines a building. Who or what we are, how we behave, the individual, our overall phenotype is NOT determined SOLELY by our genes, but more significantly by the interaction between our genes and the environment. So, for example, having a genetic risk or family history of diabetes does not mean you will manifest diabetes, it means that you are forewarned and should manage your lifestyle in a way to PREVENT diabetes.

Dr Allana Roach is a Human Geneticist and Community Health Specialist. A graduate of Howard University (USA), she is also a former faculty member of the Howard University College of Medicine and former programme drector of the Programme for Transdisciplinary Genomics at the National Human Genome Center in Washington, DC. She has over ten years of experience in the conduct of health-related human genetics research. She currently serves on the Sample Governance Committee of the National Eye Survey of Trinidad and Tobago.