Genomics is a fascinating offshoot of genetics that aims to find answers to the most intriguing questions of life: Why do we resemble our parents? How do viruses hijack cells? How does a single cell grow into a whole human? Why are some diseases more common in some races than in others?
With the advent of new technologies, this branch of medical science has been completely revolutionised over the past thirty years: we now know the complete sequence of the human genome.
By understanding the mechanism by which the blueprints for life are passed through generations, we’re also able to understand how variations in these blueprints, otherwise essential for evolution, can cause disease.
Some Fascinating Facts About our Genes
Humans, like every other organism, are made up of cells. We come into existence as just one cell at the time of fertilisation. This cell contains two sets of genes, one from our mother and one from our father. For ease of storage and access, the genes are packaged up into 46 protein parcels called chromosomes.
As the single cell divides, the genes are copied so that every new cell possesses the full complement of genetic material. This mechanism of copying the genes is quite remarkable considering that the human body contains approximately 10 trillion cells! Genes are made of a chemical called DNA. Each cell holds an amazing two metres of DNA (deoxyribonucleic acid)-if the entire DNA contained within the cells of a human being was stretched out, it would reach to the Moon and back eight thousand times.
Humans have approximately 30,000 genes stretched out along their DNA. Each gene acts as a recipe for the production of a protein and together they make up the recipe book or blueprint for you and me. Different genes or recipes are read at different times in different cells in response to the requirements of our bodies.
DNA is composed of 2 strands of combinations of 4 chemicals, which face in opposite directions and connect pairwise to form the famous double helix shape. These 4 chemicals bear the letters A, T, C and G, which stand for adenine, thymine, cytosine and guanine.
A portion of a gene might read “TTCGACGATT” which, on its own does not make a huge amount of sense, until we learn that each three-letter sequence codes for a particular amino acid, which are the building blocks of proteins. A single gene may be many thousand letters long. When this is read by the cell’s molecular machinery, a protein is made up out of the amino acids coded for.
Proteins not only make up the structural bulk of the human body but also include the enzymes that carry out the biochemical reactions of life. The units of amino acids making up a protein are linked together in a long string; the string folds back onto itself to form a three-dimensional structure that determines the function of the protein. The order of the amino acids is set by the DNA base sequence of the gene that encodes a given protein. Genes dictate the production of proteins through intermediaries called RNA; those that actively make RNA intermediates are said to be “expressed”.
The Human Genome Project (HGP)
One of the greatest feats of exploration in human history, the HGP was an international research effort to sequence and map all of the genes – together known as the genome – of members of our species, Homo sapiens. Completed in April 2003, the HGP gave us the ability, for the first time, to read nature’s complete genetic blueprint for building a human being.
The Human Genome Project has now worked out the full human DNA sequence. By 2050, it is expected that comprehensive genomics-based health care will be the norm in developed countries. We will understand the molecular foundation of diseases, be able to prevent them in many cases and design accurate, individualised therapies for illnesses.
At the moment, several genetic tests have been developed that can predict individual susceptibility to disease. One intention of the Human Genome Project is to identify common genetic variations. Once a catalog of variants is compiled, epidemiological studies will tease out how particular variations correlate with risk for disease.
Having a genetic variation that predisposes you to a certain disease doesn’t mean you’re doomed. Genes interact with other genes and with environmental influences, like diet, infection and prenatal exposures to affect health, therefore there is a lot you can do to compensate for a genetic shortcoming.
There are now predictive genetic tests available for many common conditions, allowing individuals who wish to know this information to learn what their individual susceptibilities are, and to take steps to reduce those risks for which interventions are available.
Personalised Nutrition, Lifestyle Modification & Designer Therapies
The interventions could take the form of personalised nutrition: based on your genetic test results, your nutritionist will be able to recommend changes to your diet that will specifically address the problem rather than give you general advice.
For instance, not all people with high blood pressure respond to a low sodium intake and this is due to a variation in a single gene. If you know you have that gene, it will become pointless to torture yourself trying to follow a low sodium diet because that will not make any difference to your condition. Other nutritional recommendations will be appropriate for you in this case.
Similarly, there are people on a low-fat diet who still present with high cholesterol that predisposes them to heart disease. For the medical community this was, until recently, a paradox. But thanks to advancements in genetics, this mystery was recently explained: it appears that a genetic variation in the SCARB1 gene is at fault (for more information, read my article about LOW-FAT DIET FADS and the SCARB1 gene).
Another example would be caffeine tolerance in connection with which a genotype was discovered (CYP1A2) that differentiates between fast and slow metabolisers of caffeine. Depending on the category you are in, coffee can have a protective effect (fast metabolisers) or it can harm you, predisposing you to hypertension and miocardial infarction (slow metabolisers). This has nothing to do with feeling jittery or nervous after consuming coffee, it is the adenosine receptors in the brain that are responsible for that. You can still be a slow metaboliser and susceptible to hypertension and miocardial infarction even if you don’t seem to be affected by coffee in a significant way.
Another example involves Vitamin C and heart disease: it was found that genetic variants of the glutathione S-transferase (an enzyme involved in Vitamin C metabolism) modifies the body’s response to serum ascorbic acid levels. If you have a functional GST-T gene, your body preserves what little of Vitamin C there is in the blood. If you lack this gene, you have to be extra mindful about your Vitamin C intake. According to research, the GST-T gene is absent in 20% of Caucasians and 50% of Asians. However, you still need to know your individual genotype as a Vitamin C deficiency is associated with an adverse cardio-metabolic profile, in other words, you’re a lot more susceptible to developing heart disease than if you supplemented with adequate amounts of Vitamin C regularly.
A bit about Designer Therapies and the Future of Medicine
By 2020, gene therapy should also become a common treatment, at least for a small set of conditions. Also, in the near future novel drugs will be available that derive from a detailed molecular understanding of common illnesses like diabetes and high blood pressure. The drugs will be designer therapies that target molecules logically and are therefore potent without significant side effects. Drugs like those for cancer will routinely be matched to a patient’s likely response, as predicted by molecular fingerprinting. Diagnoses of many conditions will be much more thorough and specific than now: when people become sick, gene therapies and drug therapies will home in on individual genes, as they exist in individual people, making for precise, customised medical treatment. The average life span will reach 90 to 95 years, and a detailed understanding of human aging genes will spur efforts to expand the maximum span of human life.