Genes Matter
Genetics has become a crucial tool in modern medicine. Its application opens up new opportunities to better understand diseases and offer personalized medical management. In this context, genome and exome studies have revolutionized the way an individual’s genetic information is analyzed and interpreted. In this article, we explore the differences between these two types of studies and how to determine which one is best suited to each case.
What is the genome?
The genome refers to the complete genetic code of a person, including both genes (coding regions) and non-coding regions of DNA. So they sequence or read all the genetic material and provide a complete picture of your genetic information.
What is the exome?
The exome, on the other hand, refers to the part of the genome that codes for proteins, i.e. the exons. These sequences constitute only 1-2% of the entire human genome, but are of great clinical relevance, since proteins are fundamental elements in our organism, in fact 85% of the variants associated with genetic diseases are found in this part of the DNA.
Since the exome is a small part of the genome, when we sequence the whole genome we also sequence the exome. That is, the analysis of the genome provides us with the information included in the exome of a patient plus the information of its non-coding regions.
Any genetic study has a preventive or diagnostic clinical objective, both the genome and the exome are a useful tool in both areas, but it is important to know what the intended use of the test is and which genes are included in the analysis. Sometimes it can be complicated to decide which test is more appropriate, we will try to provide some information in this regard.
Genome vs. exome studies: Which genetic test to choose in each case?
When it comes to genetic testing, both genome and exome studies are excellent options that can provide valuable information about a person’s genetics and their relationship to certain diseases. Some factors to take into account in order to select the appropriate test for each case are:
1. Objective of the test
Preventive approach
When we choose a preventive test, it is considered that the person has no personal or family history of genetic disease, so we are talking about a patient who is in principle “healthy”, a factor that must be taken into account when interpreting the genetic information.
There are two possibilities:
This type of test is performed by sequencing a group of genes or from whole exome sequencing, then analyzing only the genes related to the diseases to be studied. In the case of Veritas, the myGeneticRisk test analyzes, through whole exome sequencing, genes related to relatively frequent diseases of genetic origin such as cardiovascular disease or hereditary cancer, specifically in healthy individuals.
This type of test includes all available preventive genetic information, so for its analysis it is necessary to perform whole genome sequencing, since many multifactorial diseases or pharmacogenomic markers are found in “non-coding” regions of the DNA. It is important to understand that not all whole genome tests are clinically useful, i.e. many provide information about genetic traits that are not useful to the specialist in adapting the medical management of the patient. myGenome is the first and only preventive whole genome sequencing test with clinical utility, offering the study of more than 650 diseases along with carrier status, pharmacogenomics, risk alleles, ancestry and traits.
Diagnostic approach
In case the person presents any sign or symptom of disease and it is suspected that it may have a genetic origin, we should proceed differently. We can distinguish two types of cases:
Person with suspected disease
In this case, if there is a clear suspicion of a disease, it is possible to study the group of genes most frequently associated with that pathology. To perform this type of test, the starting point is usually exome sequencing and then the genes of interest are analyzed. Some laboratories directly sequence the genes of interest. Whole exome sequencing has advantages since, by having the whole exome sequenced, if no alterations are detected in the genes analyzed, it is possible to extend the study to other genes.
Person with complex symptoms that are not consistent with a single disease.
In cases of complex phenotypes, i.e. persons presenting with clinical signs and symptoms in several body systems not associated with a single disease, a more exhaustive DNA search is necessary. Both the exome and the genome are valid for this diagnostic approach, based on the search for genetic variants in any gene that may give rise to the patient’s symptoms. In this case we do not start from a set of specific genes, but search from the patient’s symptoms.
The diagnostic yield, i.e. the cases in which disease-causing variants are found in the patient’s disease, is somewhat higher in the genome versus the exome, as it includes more DNA regions. This is even more relevant in specific pathologies where there are described disease-associated variants in non-coding regions. ExomeDx and GenomeDx are the tests offered by Veritas in this category.
Cost and time
The genome study provides much more information than the exome study, which is why the genome study tends to be more costly and time-consuming. On the other hand, exome study is faster and, in general, more affordable. Technological advances have allowed the cost of both tests to decrease in recent years, but it is still important to keep these aspects in mind.
Bibliography:
Bibiana Palao - Directora Departamento Científico
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