What is mass sequencing?

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Mass sequencing refers to a group of molecular techniques used to determine the DNA sequence we are interested in studying. In other words, mass sequencing allows large amounts of DNA to be "read" quickly and accurately. This provides detailed information about the genetic material (or genome) of a person, a tumour or a microorganism.

Mass sequencing is also known as next-generation sequencing (NGS).

Mass sequencing has revolutionised genetic testing compared with earlier techniques, as it allows millions of DNA fragments to be analysed at the same time, providing more comprehensive results in less time.

In recent years, this technology has helped to improve the diagnosis and prognosis of diseases. In some cases, it can also help doctors offer treatments tailored to each patient's characteristics. This is known as personalised medicine.

What is DNA?

To understand what mass sequencing is, it is first important to understand what deoxyribonucleic acid (DNA) is. DNA is the molecule that contains each person's genetic information and the instructions needed for the cells in the body to function.

These instructions are encoded in four bases, or "letters": A, T, C and G. The consecutive combination of these bases forms a DNA sequence.

The human genome is the complete set of a person's genetic information, that is, their complete DNA sequence. It consists of approximately 3.2 billion base pairs distributed across 23 pairs of chromosomes.

What are genes, the exome and the genome?

DNA can be studied at different levels, depending on the amount of information needs to be analysed.

Gene: a specific section of DNA that contains the instructions needed to make a protein or carrying out a particular function. We have around 20,000 genes.
Exome: the collection of the parts of genes that contain the instructions for making proteins (the exons). Although these regions account for only 1-2% of the entire genome, they contain approximately 85% of the mutations or genetic changes responsible for inherited diseases.
Genome: the complete set of a person's DNA. It includes genes and their exons, as well as the rest of the DNA regions, which can also have important functions.

Types of mass sequencing studies

Depending on the information required, different mass sequencing strategies can be used. The different tests mainly differ in the amount and type of DNA they analyse.

Targeted gene panels. These analyse a specific group of genes associated with a particular disease, such as genes linked to hereditary cancer, neurological disorders or heart conditions. They are targeted tests and are often less expensive and faster than other options.
Whole exome sequencing (WES). This analyses the coding regions (exons) of all known genes at the same time. It is useful when it is not clear which gene may be responsible for a disease, or when more common genetic causes have been ruled out. It can identify changes associated with many different genetic diseases in a single test.
Whole genome sequencing (WGS). This analyses a person's entire genome (their complete DNA sequence). Unlike whole exome sequencing, it includes both exon regions and the rest of the genome. It can detect genetic changes that other tests may not identify and provides the most comprehensive view of a person's genetic information.
Microorganism sequencing. This analyses the genetic material of bacteria, viruses, fungi and other microorganisms to better understand their genetic characteristics, identify specific variants and detect possible resistance to treatments.