DNA. A mere three-letter word. The power that lies within though is beyond phenomenal, and we have only started to unwind the marvels of its intricacies. We have come a long way since the discovery of the DNA in 1953. We undertook the ambitious human genome project in 1990[1], which took us 13 years and 3 billion dollars to complete. Only 20 years have gone by and today, we are already planning $100-$1000 genomes.
The tiny 0.1% difference that exists between you and me is the magic that makes you, you and me, me. It defines the colors of our eyes, the different shades of our skin, our differing hair tones and whether we have that little dimple when we smile. Isn’t it remarkable that this tiny difference is all that makes us so distinctly different and so beautifully unique?
So much packed within the DNA. So much we know about it and yet so little do we.
But what use is all this sequencing and technology if we can’t use it to better our lives and of those around us? This article is a modest attempt to condense and highlight the various types of genetic tests and how we can use them. Isn’t it time to listen to what our DNA is telling us?
There are different things our DNA can tell us, as we grow within the comfort of our mother’s womb, and as we grow through adulthood and become parents ourselves. At all these stages, we can ask our DNA different questions – and get different answers.
Even before we plan to conceive a baby, we can choose to check whether we are “carriers” of a specific genetic mutation, one that we might pass on to our children (carrier testing)[2]. Carriers may not be symptomatic of the disease, and hence, these traits can secretly pass through generations without ever being detected, much like a silent volcano under the sea. Carrier testing is relevant to individuals with a family history of a certain genetic disorder. Even though there are hundreds of recessive genetic disorders, most of them are very rare. However, certain ethnic groups have an increased risk of specific genetic conditions[3]. Individuals who are carriers have a 25% chance, in each pregnancy, of having a child with that specific autosomal recessive disorder[4].
If DNA gives a discomforting answer in the carrier test, a couple can opt for preimplantation testing[5] or preimplantation genetic diagnosis (PGD)[6]. PGD is a specialized technique used during embryo selection during in vitro fertilization (IVF). IVF involves removing egg cells from a woman’s ovaries and fertilizing them with sperm cells in vitro (outside the body). In preimplantation testing, genetic mutations are tested for in a small number of cells taken from these embryos. Only unaffected embryos are implanted in the uterus to initiate a pregnancy, lowering the risk of having a child with a particular genetic or chromosomal disorder[7].
Once in the 1st or 2nd trimester of pregnancy, prenatal testing[8] may be performed, if there is an increased risk that the fetus might have a genetic or chromosomal disorder. Prenatal tests can help identify whether your baby is more or less likely to have inherited genetic disorders[9].
9 months later, a baby enters the world. As precious as it is, so much more important is to do newborn screening[10]. Internationally recognized as an important preventative health program, newborn screening aids in early detection, diagnosis and treatment of certain genetic, metabolic and even infectious congenital disorders, significantly reducing disease development, associated disabilities and mortality rates. Although the newborn disorders being screened varies between hospitals, these four most common genetic diseases are often included: 1. Phenylketonuria (PKU), 2. Congenital Hypothyroidism (CH), 3. Galactosemia (GAL) and 4. Sickle Cell Disease.
The answers we get from prenatal and newborn screening have helped dramatically reduce the rates of morbidity and mortality of babies with genetic disorders all around the world.
Disorders sometimes only appear after birth, often at later stages in life. Predictive testing[11] can help identify mutations that increase a person’s risk of developing genetic disorders, such as certain types of cancer. Presymptomatic testing[12] may aid in determining whether a person will develop a genetic disorder before any signs or symptoms appear. These tests are not to be taken lightly due to the implications of their results. The answers from these DNA tests can provide information about a person’s risk of developing a particular disease and help to make informed decisions about future medical care.
Sometimes, particular conditions can only be predicted or suspected based on physical signs and symptoms. That’s when diagnostic testing[13] can act as an additional tool to identify and confirm a diagnosis. The results from this type of testing can help one make informed choices about health and management of the disorder, much like carrier testing.
Talking about health and management, DNA testing like pharmacogenomics (PGx) testing[14] is challenging our current medical paradigm of “one size fits all”. Naturally, not all of us react the same way to medications (think alcohol or caffeine). In fact, drugs can be ineffective for up to 95% of patients (for example. high cholesterol medications)[15]. Knowing our DNA and what it encodes for might just be a step closer in personalizing medicine specific to any individual. Optimizing treatments based on our DNA eliminates the need for the long and tiring “trial and error” methods of prescribing, reduces the risk of potential side effects and improves therapeutic efficacy.
As much as our DNA can guide us in planning and managing our lives better, it also offers some playful information, making us connect with our past – centuries of our past, embedded somewhere in the DNA we carry within. Genetic ancestry testing[16] offers great predictions about where an individual’s ancestors might have come from and about relationships between families. As smart as it is, DNA can sometimes leave traces too – specific patterns of genetic variations are frequently found in people of similar backgrounds and the more closely related we are (families, populations, etc.), the more patterns of variations we would share. However, there are various limitations as well due to a limited database of genetic variants on specific ethnicities and human migrations, for example.
All these give an idea of how serious answers may be as we seek our genes.
However, DNA certainly has a fun side to it too. Why not have fun with some “Recreational DNA testing”? The triple helix is not always serious, for it is able to tell if you might have athletic genes, can recommend a great wine for you, guide your fat loss and even help in optimizing your sleep, to name a few.
Throughout our lives, we can keep asking our DNA for answers. Some of which we might get and some of which we will not. Some of which are serious, some of which are silly, some of which are just reflecting its playful nature and some, it’s secret side. DNA is after all, only a part of us and we are what it is.
About Mathura:
Mathur
a Shanmugasundaram, PhD is a geneticist who is deeply passionate about personalized medicine and believes in using advances in science and technology to optimize and improve healthcare.
Editors: Sayantan Chakraborty, PhD, Rituparna Chakrabarti, PhD and Sushama Sivakumar, PhD
Illustration: Fuzzy Synapse
[1] https://www.genome.gov/10001772/all-about-the–human-genome-project-hgp/
[2] “Genetic Screening Tests – Autosomal Recessive Diseases”. OB/GYN Specialists of Palm Beaches, P.A.
[3] The American college of Obstericians and Gynecologists, Carrier Screening for Genetic Conditions, Number 691, March 2017
[4] NIH Genetics Home Reference: https://ghr.nlm.nih.gov/
[5] Brezina PR and Kutteh WH (2015). Clinical applications of preimplantation genetic testing. BMJ 19:350, 7611.
[6] Harper JC. Introduction. Harper JC, Delhanty JDA, Handyside AH, eds. Preimplantation Genetic Diagnosis. London, UK: John Wiley & Sons; 2001. 3-12.
[7] American pregnancy association: http://americanpregnancy.org/infertility/preimplantation-genetic-diagnosis/
[8] Latendresse G and Deneris A (2015). An update on current prenatal testing options: first trimester and noninvasive prenatal testing. 60: 24-36.
[10] Centers for Disease Control and Prevention: https://www.cdc.gov/newbornscreening/
[11] Mitchell PB et al., Predictive and diagnostic genetic testing in psychiatry. Psychiatr Clin North Am. 2010; 33(1): 225-43
[12] Genetic Diagnosis and Testing in Clinical Practice. 2006. Clinc Med Res (4): 123-129.
[13] http://emedicine.medscape.com/article/773832-overview
[14] Relling MV and Evans WE (2015). Pharmacogenomics in the clinic. Nature (52): 43-350.
[15] Schork, N (2015). Personalized medicine: Time for one-person trials. Nature. 520, 609-611.
[16] Kirkpatrick BE and Rashkin MD (2017). Ancestry Testing and the Practice of Genetic Counseling. J Genet Couns. 26: 6-20.
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