How is DNA extracted from blood and saliva used?
Extracting DNA from blood seems like a forensic practice we'd see on TV shows, but what's its purpose? While blood is one of the most common samples used to extract DNA, there are other sources from which DNA can be obtained.
What is DNA?
To begin, let's look at what DNA is and what its function is in the human body. The abbreviation DNA stands for deoxyribonucleic acid, DNA, a complex molecule, is the fundamental component of an individual's genetic material. It contains the instructions necessary to create and maintain life.
These instructions are written in a code with four letters that correspond to four molecules: Adenine (A), Thymine (T), Cytosine (C) and Guanine (G), which join together in a specific way, A joins with T and C with G, forming a double helix or spiral staircase.
The complete DNA sequence is called genome.
Essentially, it's our genetic code. Every cell in our body—with few exceptions—contains a copy of our entire genome. We might imagine DNA as a single, long molecule floating freely within our body's cells, but it's actually located in the cell nucleus, tightly bound to specific proteins.
Interestingly, although we all have very different characteristics from each other, and it is our particular genetic code that determines our individual traits, most of the DNA (99,9%) is the same in all humans.
Differences between somatic and germline DNA
It is important to differentiate between somatic DNA and germline DNA. During embryogenesis, all human beings are formed from the union of an egg and a sperm. The genome of the new living being will be formed with part of the mother's and father's DNA, and all the cells that arise from the zygote will have the same genetic material, which is known as germline DNA. As we age, tissues may acquire certain genetic variations or mutations that are not present in the rest of the body. Therefore, when we obtain a sample of a specific tissue and analyze its genetic material, it is known as somatic DNA. This is why there can be small differences between somatic and germline DNA.
Function of DNA: our genetic code
We could define our genetic code as our life's blueprint. This means that DNA contains all the necessary and fundamental information for our growth, reproduction, and health. Furthermore, although every cell has the same information, the specific information activated depends on its type, from neurons to muscle cells. Finally, DNA determines our defining characteristics, from our eye color to our fondness for sweets or whether we are prone to certain injuries or diseases.
Given all the information contained in DNA, it's easy to see its importance for study. Any change in the DNA sequence can lead to potential diseases, vulnerabilities, or genetic traits, depending on the type of genetic variation.
Can DNA be extracted from blood?
So far, we've seen that DNA is present in virtually every cell in our body. Therefore, DNA can be extracted from blood; in fact, this is one of the most commonly used sources for genetic testing. However, leukocytes are the only blood cells that have a nucleus and, therefore, the only ones that contain DNA. To explain how DNA extracted from blood and saliva is used, we'll need to clarify that extracting DNA from blood means specifically analyzing the DNA contained in leukocytes.
How is DNA extracted from blood?
The first step is to obtain a blood sample, which requires a qualified person or a phlebotomist to perform the puncture. It is a minimally invasive procedure. Once the blood sample arrives at the laboratory, technicians will process it to obtain purified DNA. This requires many instruments and machines, as well as a large quantity of reagents. The blood sample is homogenized by inversion, that is, by turning the blood tube upside down to obtain a uniform sample. Once homogenized, the DNA is extracted. Inside the cells, we can find many different organelles and structures that must be removed to purify the DNA. To do this, we must lyse the cell, that is, break down all the membranes, and add a reagent called protease to remove all the proteins. Finally, after all these processes, we will have our isolated DNA.
Today there are devices and machines that allow the entire process to be automated; that is, you can introduce the blood sample into the system and obtain the isolated DNA.
Why use blood to extract DNA?
When it comes to genetic testing, blood is an easily accessible resource, since a simple venipuncture yields a large quantity of DNA, usually of high quality. Once the blood is drawn, it is recommended to perform the tests as soon as possible to prevent the cells and DNA from deteriorating.
Saliva as another source of DNA
In recent years, the use of saliva for genetic testing has become widespread. It can be easily obtained by inserting a cotton swab into the mouth and wiping it across the cheeks, or from a saliva collection kit. The advantage of using saliva is that it allows for self-collection; that is, there is no need for a trained professional to collect the sample. It is a relatively quick procedure, and the sample can be stored at room temperature for longer periods.
Other sources of DNA
Apart from blood and saliva, there are other sources of DNA that can be used in different circumstances:
- Sperm: A specific analysis is performed to check male fertility, including DNA fragmentation.
- Fabrics: In some cases, a patient may be referred for a biopsy of a specific tissue. This can occur when a tumor is found and a genetic analysis is performed to check for mutations in the genetic material, which in this case would be somatic DNA.
- Amniotic fluid or chorionic villi: These types of samples are used in prenatal diagnosis when a suspected genetic disease is identified during pregnancy, to analyze the genetic material of the fetus.
- Hair root: It is primarily used for forensic analysis and paternity testing.
The importance of DNA and genetic testing
Since our DNA contains all our essential genetic information, extracting and studying it can yield a wealth of important data about our health, genetic predispositions, and much more. Today, there are many uses for a DNA sample, including:
- To help diagnose genetic diseases when a person already has signs and symptoms.
- Identifying our risk to certain diseases and helping us take preventive measures to avoid their onset or detect them as early as possible.
- Prenatal diagnosis is used when a suspected genetic disease is identified during pregnancy. In this case, the DNA sample is obtained from the amniotic fluid or chorionic villi.
- Non-invasive prenatal screening using a sample of the mother's blood; current technology allows analysis of cell-free fetal DNA present in maternal blood.
- Establish carrier status to know if we are carriers of a disease transmissible to our offspring.
- To help understand how our body reacts to drugs for more effective treatment and to avoid drug reactions.
- To help understand our predisposition to certain multifactorial diseases.
Extracting and analyzing DNA from blood or other sources can be extremely beneficial for understanding our genetic makeup, determining if we have a greater predisposition to common diseases, and much more. Since DNA is the instruction manual for life, having access to this data can prevent the development of serious illnesses or detect them in their early stages and can help us better understand our path through life.
At Zogen we understand the importance of DNA, which is why we offer different genetic studies ranging from preventive medicine to prenatal diagnosis. We are opening the door to a broader use of genetic services, not only focused on diagnosis, always with genetic counseling provided by our team of medical geneticists. If you would like to receive more information about the services we offer, contact us!
Fountain: Veritas Int.
