DNA extracted from blood and other sources: how is it used in genetics?

Extracting DNA from blood sounds like a forensic practice we would see on TV shows, but what is its utility? While blood is one of the most commonly used samples to extract DNA, there are other sources from which DNA can be extracted.

What is DNA?

To begin with, let’s cover what DNA is and its role in the human body. The abbreviation DNA stands for deoxyribonucleic acid, a complex molecule. This is the fundamental building block for an individual’s entire genetic makeup. DNA contains the instructions needed 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 are joined together in a specific way, A joins with T and C with G, forming a double helix or spiral staircase.

The complete sequence of DNA is called a genome. This is essentially our genetic code. Every cell in our bodies – with few exceptions – contains a copy of our complete genome. You could imagine the DNA as one single long molecule that is free inside our body’s cells but it is always located in the nucleus of the cells and it is also closely attached to specific proteins.

Interestingly, although we all have very different characteristics from one another, and it is our particular genetic code what determines our individual traits, the largest part of the DNA (99.9%) is the same in all humans.

Differences between somatic and germline DNA

It is important to differentiate between somatic 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 made with part of the mother´s and the 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 get older, it is possible that tissues may acquire certain genetic variations or mutations that are not present in the rest of the organism, so when we obtain a sample from a specific tissue and analyse its genetic material, this is known as somatic DNA. This is the reason why there may be small differences between somatic and germline DNA.

DNA function: our genetic code

We could define our genetic code as our map of life. This means that the DNA contains all the necessary information fundamental to your growth, reproduction, and health. Moreover, although each cell has the same information, depending on its type, the information needed for each cell will be activated, from neurons to muscle cells. Finally, DNA determines our characteristic traits, from the colour of our eyes to our love of sweets or whether we may be prone to certain injuries or diseases.

Looking at all these types of information all contained within DNA, it is easy to see its relevance for studying it. Any changes within 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?

We have seen so far that DNA is present in virtually every cell in our bodies. Consequently, you can extract DNA from blood – in fact, this is one of the most commonly used resources for DNA testing. However, leukocytes are the only blood cells that have a nucleus and, therefore, the only ones that actually contain DNA. So, extracting DNA from blood means analysing the DNA contained in leukocytes specifically.

How is DNA extracted from blood?

The first step is to obtain a blood sample which requires a qualified person or phlebotomist to perform the puncture. It is a minimally invasive procedure. Once the blood sample arrives to the lab, the technicians will process the sample to obtain the purified DNA. For this, many devices and machines are needed, as well as a lot of reagents. The blood sample is homogenized by inversion, in other words, by turning the blood tube upside-down to obtain a uniform sample. Once homogenized, the DNA is extracted. As you probably know, inside the cells we can find a lots of different organelles and structures that we need to get ride off to purify the DNA. For that we need to lyse the cell, which means to break all the membranes and then add a reagent called protease to remove all the proteins. Finally, after all these processes we will have our DNA isolated.

Nowadays, there are devices and machines which allows to automatize the whole process meaning you can enter the blood sample into the system and obtain the isolated DNA sample.

Why use blood to extract DNA?

When it comes to genetic testing, blood is an easily accessible resource, with a venous puncture yielding an abundant amount of DNA, usually of high quality. Once blood has been taken, it is recommended to conduct tests as soon as possible to prevent the cells and DNA from any deterioration.

Saliva as another source of DNA

In recent years the saliva has been widely used for genetic testing. It can be easily obtained either by inserting a cotton swab into the mouth and swiping across the cheeks, or from saliva sputum. The advantage of using saliva is that allows the self-collection, there is no need of a qualified person to take the sample, it is a relatively fast procedure, and can be stored at room temperature for longer periods of time.

Other sources of DNA

Apart of 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.
• Tissues: in some cases, a patient may be referred to perform a biopsy of specific tissue, this may occur when a tumor is found and a genetic analysis is carried out to check for mutation in the genetic material, which in this case it would be somatic DNA.
• Amniotic fluid or chorionic villi: these types of samples are used in prenatal diagnosis when a suspected genetic condition is identified during pregnancy, to analyse the genetic material of the fetus.
• Hair root: it is mainly use for forensic analysis and paternity testing.

The importance of DNA and genetic testing

Since our DNA holds all our essential genetic information, extracting and studying it can yield a lot of important data for our health, genetic predispositions, and more. Nowadays there are many uses which can be performed on a DNA sample, including:

• Help diagnose genetic diseases when a person already has signs and symptoms.
• Identify our risk to certain diseases and help us take preventative measures to avoid their onset or to detect them as soon as possible.
• Prenatal diagnosis when a suspected genetic condition is identified during pregnancy. In this case, the DNA sample is obtained from the amniotic fluid or from chorionic villi.
• Non-invasive prenatal screening using a blood sample from the mother; current technology allows to analyse free fetal DNA present in the mother blood.
• Establish the carrier status to know if we carry a disease that can be transmitted to our offspring.
• Help understand how our body reacts to drugs for a more effective treatment and to avoid pharmacological reactions.
• Help understand our predisposition to certain multifactorial diseases.

Extracting and analysing DNA from blood or other sources can be extremely beneficial for understanding our genetic makeup, our health predispositions, and more. Since DNA is the instruction book of life, having access to this data may prevent serious diseases from developing or detecting them in early stages and can help us better understand our pathway in life.

At Veritas, we know the importance of DNA, therefore we offer different genetic studies that cover from preventive medicine to prenatal diagnosis. We open the door to a wider use of the genetic services not only focus on diagnosis always with the support of our genetic counselling consultations by medical geneticists. If you would like to receive more information about the services we offer, do not hesitate to contact us.