In our article today on World DNA Day, we want to shine a light on the terminology and differences between genetics, genomics, and epigenetics, as well as their application in this exciting science of our genes and DNA.
The study of DNA for diagnostics in healthcare is relatively young compared to other disciplines in medicine. However, after decoding most of the entire human code – thanks to the Human Genome Project in the early 2000s – the application of genetic testing has accelerated and brought up multiple new fields within this type of diagnostics.
What is Genetics?
Our DNA makes up the fundament for multiple reactions within our body at such a core level that it can be seen as the “blueprint” for life; for more information, you can check out our previous article What is DNA, and what is its size?. When talking about our DNA – in a medical setting – there are two terms usually floating around most of the time: Genetics and Genomics. Both describe the study of DNA with a different focus.
The term genetics means the study of single genes and how our traits or conditions related to these genes are passed down from our parents to us and further to our children – one could say the legacy on a molecular basis. When genetics is used in the medical diagnostic setting, it describes the genetic factors most of the time, the variation of genes or bases on the DNA which might cause disorders or diseases. For example, two diseases that are already well described and usually caused by a faulty gene are Huntington’s disease or cystic fibrosis.
Chorea Huntington or Huntington’s disease is a dominantly inherited neurological illness causing involuntary movements, severe emotional disturbance, and cognitive decline. This illness has its source in a faulty version of the HD gene on chromosome 4, which causes malformation of the huntingtin protein. As the defective version of the HD gene is passed on dominantly, children of a parent who has Huntington’s disease have a 50 50% chance of inheriting this disease, which has its onset usually around mid-life. 
Huntington’s disease has no cure so far. Although testing can be carried out reasonably easily since the discovery in 1993, the decision to be tested for this disease is rather difficult. But hope is on the horizon as scientists at the University of California at Irvine discovered how the genetic mutation alters chemical pathways to cause the disease. That newly found information could be used to develop a treatment that might slow down or prevent the disease.
In the United States, cystic fibrosis is the most common, fatal disease that can be caused by more than 900 known variations inside the CFTR gene. The CFTR protein is responsible for the transmission of chlorides and other ions, thus regulating the salt balance inside the cells.
Nowadays, almost every state in the US is routinely screening newborns for cystic fibrosis. Screening newborns mean allowing early detection to gain precious time for the personalized treatment of the disease. Genetic testing is usually carried out after initial tests such as blood or sweat tests hint at the disease.
What is Genomics?
The term genomics appeared more recently, as the sequencing techniques became more sophisticated and more regions of our DNA were examined due to the decrease in costs involved. Genomics is the study of all of an individual’s genes the so-called genome. In genomics, the interactions of those genes with each other and with the person’s environment are studied to gain insights into more complex diseases such as cardiovascular diseases, cancer, or diabetes. The complexity comes from the potential combination of multiple genetic and environmental factors that lead to the condition and allows a more realistic answer to why an illness occurs.
Genetics and Genomics and the global sharing of variants connected to specific phenotypes have paved the way for new possibilities in therapies and treatments. Helping patients worldwide understand more about their potential inherited disease, researchers can gain more knowledge about the pathways of our bodies and lead to new cures.
As for a concrete example, let’s look at pharmacogenomics. Pharmacogenomics studies a person’s DNA information regarding how a specific drug is metabolized. Since our DNA provides the blueprint for most proteins, it is also responsible for receptors – built of proteins – within our body to which drugs attach and function. By looking at the DNA sequence and potential variations, previously described as affecting the transportation and/or the metabolization of medicine inside us, pharmacogenomics can provide insight into what drug is the most beneficial or about the dosage necessary to work and minimize side effects.
In this context, pharmacogenomics is becoming an important tool for drug discovery, using drug-dependent patterns of global gene expression as biologically relevant endpoints. The spotlight is on genomic tests that provide information about DNA sequence that may correlate with the phenotype (drug effect). Given the flood of genomic data, bioinformatic algorithms are needed to identify those genes that genuinely provide insight into drug efficacy.
What is Epigenetics?
Compared to genetics and genomics, epigenetics studies the changes in gene functions that are not attributed to alterations of the DNA sequence but to the higher structure of genetic material. The term epigenetics contains the Greek prefix epi, which means above. 
The structure of our DNA is made up of 4 levels, and epigenetics is the study of the secondary, tertiary, and quaternary structure of the DNA and the resulting changes in gene expression. The epigenetic marks, collected in the epigenome, determine how genes are expressed and can be a possibility to differentiate the cells by their specific gene expression levels. Any cell has its specialized epigenetic pattern. There are two types of modifications: DNA methylation and histone modification. So if we know the typical methylation pattern and then look at the methylation pattern in, for example, a tumor cell, we can see what changes are taking place and what genes are affected.
So, epigenetics tries to shine a light on how the above layers of our DNA might be responsible for certain diseases, further understand the pathways and develop epigenetic drugs to improve treatment. Today the inhibition of specific epigenetic enzymes can reverse the incorporation of an epigenetic mutation, making them attractive targets for cancer therapy. In the United States, some epigenetic drugs to treat mainly hematological malignancies are already approved by the FDA.
In the future, experts see epigenetic drugs to be part of combination therapy in cancer with chemotherapy and radiation. Epigenetic drugs can target cancer cells and make them more sensitive to radiotherapy, thus lowering the entire dosage of radiation or chemotherapy to deviate damage solely to the harming cancer cells and lowering the massive side effects.
By Lucas Laner on April 25, 2022.
 Megan Molteni. The WIRED Guide to Genetic Testing (2019). https://www.wired.com/story/what-is-genetic-testing/
 National Human Genome Research Institute. Genetics vs. Genomics Fact Sheet (2018). https://www.genome.gov/about-genomics/fact-sheets/Genetics-vs-Genomics.
 National Human Genome Research Institute. About Huntington’s Disease (2011). https://www.genome.gov/Genetic-Disorders/Huntingtons-Disease
 National Human Genome Research Institute. About Cystic Fibrosis (2013). https://www.genome.gov/Genetic-Disorders/Cystic-Fibrosis
 Mayo Clinic; Cystic Fibrosis (2022). https://www.mayoclinic.org/diseases-conditions/cystic-fibrosis/diagnosis-treatment/drc-20353706
 Pollard HB, Eidelman O, Jacobson KA, Srivastava M. Pharmacogenomics of cystic fibrosis. Mol Interv. 2001 Apr;1(1):54-63. PMID: 14993338; PMCID: PMC8364423.
 Laura Elnitski; Epigenetics (2022). https://www.genome.gov/genetics-glossary/Epigenetics
 Matthew Wygant; Clinical Applications of Epigenetics (2019). https://www.biocompare.com/Editorial-Articles/363138-Clinical-Applications-of-Epigenetics/
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