How are genetic tests performed?

How is genetic testing done?

The field of molecular genetics has developed significantly and rapidly, these developments are reflected in the understanding of various genes. For example, diseases with an underlying source that previously went unknown have been discovered as being genetic disorders, that can easily be prevented ahead of time. Researchers and healthcare providers can study cancerous tumors to determine the most effective form of therapy. Elderly people can assess their risk for developing certain diseases through testing only a few cells, without the need for large tissue samples.

A wide variety of genetic testing techniques are available today. This article will discuss several common methods.


Detecting the gene mutation by screening known mutations

To detect a specific gene mutation, it is not always necessary to interpret DNA in its entirety, since there are many mutations that have already been fully interpreted. Instead of analyzing all the base-units (or genetic alphabet) of a selected gene, researchers can focus on the bases in which mutations are known to occur.

This method allows testing family members with a genetic disorder, and after detecting the gene mutation, using this information to continue testing other members of the family. In the same way, a fetus can be genetically tested while still in the womb to determine whether it is a carrier of the known mutated gene.

In cases where no family members have developed the disorder, or when family members cannot be tested for various reasons, genetic testing can focus on gene mutations prevalent in the patient’s ethnic descent group.


Genetic sequencing (exome sequencing)

In certain cases, the mutation consists of a change in one of the nucleic acids in the DNA sequence that occurs in a different “building block” in each patient. In these cases (especially when testing family members is not possible) a process called Exome sequencing is required. Exome sequencing is first performed on a single family member who has developed the disease and only after the gene mutation has been identified can this test be performed on other family members (including fetal testing during pregnancy).

Exome sequencing is considered expensive and time-consuming. When couples considering having children have a family member with a certain genetic disorder, it is recommended they wait until receiving the sequencing results, before conceiving.


Detecting mutations without sequencing

Genetic tests that do not include full DNA sequencing are usually considered faster and less expensive. These tests can detect many, but not all, types of mutations.

This test is only performed on people who have a genetic disorder. The suspected gene is divided into short fragments, that are attached to identical fragments from a healthy sample in a laboratory. If the tested segments are healthy, an attachment will occur. However, if one of these fragments contains a mutation, attachment will not occur. This allows determining which part of the gene contains a mutation, thus saving precious time.


Protein truncation test – testing gene products

When a gene is very large and the variety of possible mutations is extensive, gene products can be studied rather than the gene itself. This method is usually applied to genes that are shorter or longer than usual (with missing or excess nucleotides), which results in a shorter (or longer) length of protein produced by these genes. Proteins that are truncated indicate a gene mutation. Although this test is considered simple and inexpensive, its downside is the fact it cannot detect all cases of gene mutations.


Next-generation sequencing

Until recently, genetic screening could only test one gene at a time. Next-generation sequencing processes the entire genome. This way, a single test can interpret all the patient’s DNA. Hopefully, the more genetic diseases are discovered and researched, this test’s high cost will become more worthwhile.

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