How Genetic Testing Shaped Modern Medicine
How does genetic testing function? A DNA sample is extracted usually through saliva, blood, or cheek cells and is placed on chips with hundreds of thousands of probes.
The year is 2050 and Cure to Cystic Fibrosis Discovered, Customise Your Child, App to Reach 150 Years with Personalised Medical Treatments, and Antibiotic-Resistant Superbugs Defeated are all headlines of the past few years.
None of these medical feats would have been possible without the advent of genetic testing. However, to better understand what the future of genetic testing holds one must reflect on our past and go back to the year 2020.
First, it is crucial to understand what are genes and DNA that make us unique. Deoxyribonucleic acid (DNA) is the molecule that withholds the genetic code of organisms.
All the DNA information, the genome, is stored as a code of four chemical bases which are adenine (A), guanine (G), cytosine ( C ), and thymine (T).¹ The genome is all of an organism’s DNA including the bases necessary to read and maintain it.
The chromosomes inside the nucleus of a cell are the DNA molecules which hold the genome of an organism. Inside of the 23 chromosome pairs, there is a code encrypted with about 3 billion letters of the chemical bases A, C, T, and G. Cells decode these letters into 3 letter amino acids which are the building blocks of proteins.² The order of these letters is the genome sequence.
From decrypting the meaning of this code we can achieve medical feats such as picking the ideal drug to beat a cancer diagnosis, uncovering our ancestral homelands, discovering abnormalities of an unborn baby and identifying risks of diseases one might develop.
Homo sapiens have over 99% of the same genome sequence. However, this leaves us with 3,000,000 base pairs of variation that make us unique.
So, you might ask yourself what exactly genetic testing is. Genetic testing is a type of medical test that points out changes in chromosomes, genes, or proteins.
Genetic tests can diagnose or rule out a suspected genetic condition or calculate the chance you will develop or pass on a genetic disorder. In theory, there are currently three main different methods of genetic testing.
The first one is a gene test or more precisely a molecular genetic test which examines single genes or short parts of DNA to pin down mutations that can lead to a genetic disorder. The next type is the chromosomal genetic test that scans whole chromosomes to identify large genetic changes such as a copy of a chromosome.
These tests can be used for prenatal testing to identify if an unborn child will have Down or Edwards syndrome caused by a duplication of chromosome 21 and 18, respectively. The final main method is a biochemical genetic test that measures the amount and activity of proteins to indicate variations in DNA which may account for a genetic disorder.³
How does genetic testing function? A DNA sample is extracted usually through saliva, blood, or cheek cells and is placed on chips with hundreds of thousands of probes. Probes are single strands of DNA that emit a bright burst when a matching sequence is discovered.
These microarrays search through a person’s genome for single nucleotide polymorphisms (SNPs) which are variants.¹ SNPs are used to find out the probability for a person to develop a certain disease or illness.
The reason that genetic testing has revolutionized today’s medicine is its numerous fields of application. It is possible to diagnose a genetic condition which is key for appropriate treatment.
Furthermore, if one is found to be prone to a genetic condition, then regular check-ups and precautions can be taken to reduce the risk factor.
Genetic testing can also be used to test for inherited conditions such as Huntington’s disease or cystic fibrosis which are linked to monogenic conditions. Pharmacogenetics is another important application of genetic testing which helps identify the most effective medication and dosage for a disease.
Carrier testing is important for prospective parents to test if both have a copy of genetic mutation which causes a genetic disorder when two copies are prevalent. An example of this disease is sickle cell anaemia.⁴
Many of these genetic tests are useful during pregnancy and infancy. For example, prenatal testing can detect abnormalities of an unborn baby’s genes. Recently a new method of prenatal testing has been developed which can detect baby’s DNA via a pregnant mother’s blood.
Genetic testing has additionally found its way to the in vitro fertilization clinic where embryos are tested for genetic abnormalities before implantation in the uterus.
The most common type of genetic testing is newborn screening. Newborns are tested for genetic and metabolic abnormalities.⁴ Detecting these abnormalities early means that care and treatment can start right away.
The ideal way to experience the genetic advancements would be by travelling through the decades. We could imagine that we are in the year 1866 when Augustinian Monk, Gregor Mendel, published his most notable scientific paper that showed how characteristics are inherited.
He experimented on pea plants from 1856 to 1865 and discovered that genes come in pairs (chromosomes) and are inherited from each parent.⁵ Mendel discovered dominant and recessive traits which are important when comparing children’s genomes to their parents’.
The next breakthrough was the discovery of the double-helix structure of DNA by James Watson, Francis Crick, and Rosalind Franklin in 1953. When the two strands are separated two identical molecules are created.
This was a milestone in science that boosted molecular biology and helped genetic testing become a reality.⁶ Three years later karyotyping was invented. Karyotyping is the staining of chromosomes making it able for them to be sorted and counted.
Experiments proved that humans have 46 chromosomes whereas people with specific genetic disorders have extra copies of chromosomes such as people with Down syndrome having an extra of chromosome 21. It was discovered that only 2% of the genome codes for proteins and the rest is “junk DNA”. In 1984, British Alec Jeffreys found the use of “junk DNA” for forensics.
The geneticist discovered that the genome sequence repeats itself in “junk DNA”. The number of short tandem repeats (STRs) is unique to every person and can create a DNA fingerprint. Only three years later the first arrest was made by tracing DNA from a crime scene.¹
The Human Genome Project was the international research project to determine the sequence of the human genome and was groundbreaking for genetic testing.
The United States with international partners including the UK worked from 1990 to 2003 to understand the blueprint of a human and the function of specific genes and proteins. On June 26th, 2000 the first draft was publicized and the final version was released in 2003.⁷
Today genetic testing is becoming more accessible to the public. Currently, there are over 250 different direct-to-consumer tests that offer to decrypt your ancestral past and genetic future. Genealogists are trying to transform this data to create family trees.
By looking at our genome sequence one can get a polygenic risk score which indicates the likeliness of developing a disease such as heart disease or breast cancer.¹ Doctors can prescribe medicine and take extra precautions for high-risk patients.
Already today there are a plethora of uses for genetic testing but what does the future hold? Tests will become more accessible and will become more budget-friendly. Therefore, the data input will increase immensely, and these tests will become more accurate.
In the future, one of the goals is to catch diseases before symptoms appear. In in vitro fertilization clinics, wealthy parents might be able to add a couple of centimetres and IQ points to their future children.¹ Hospitals are going to have whole genome prenatal-screening programs.
The future of genetic engineering already exists and it’s CRISPR gene editing. It is a system that can cut and replace genes into DNA. A protein called Cas9 together with CRISPR sequences can break apart infectious nucleic acid.⁸
Already today this system is being used to implement pig kidneys for organ transplants. Many people that used pig kidneys for transplants contracted the porcine disease but now the genes responsible can be deleted.
Additionally, in the future one will be able to edit genes of a human embryo and delete genes linked with diseases. A growing problem that is said to be unstoppable in the next 50 years is antibiotic-resistant bacteria. CRISPR might be able to fight this superbug by making them destroy themselves.⁹
With such revolutionary testing, precautions need to be taken to prevent dystopian futures. It will be key to establish data protective policies and secure databases to store our genome sequences. Additionally, testing should be performed on all races to provide accurate polygenic tests which are currently race-specific.
Also, it will be important to set moral, ethical, and social boundaries about how we use the information provided by these tests.
One can say that genetic testing is shaping modern medicine in numerous ways from pre-diagnosis to identifying the most beneficial treatments for cancer patients. The future withholds endless opportunities with technologies like CRISPR, however, with great power comes great responsibility.
Engineer and columnist passionate about technological and scientific advancements that improve life on Earth.