Genetic Studies

General Description

Genetic tests are a series of procedures carried out in specialized laboratories with the goal of studying a person’s DNA to check for any modifications in genes, chromosomes, or proteins.

DNA, or deoxyribonucleic acid, is the molecule that contains an organism’s genetic information. It is primarily located in the cell nucleus, though a small portion is found in the mitochondria. DNA consists of two long strands intertwined to form a spiral known as a double helix. Each strand is made up of nucleotides, which are units composed of a sugar, a phosphate, and a nitrogenous base. There are four types of nitrogenous bases—adenine (A), guanine (G), cytosine (C), and thymine (T)—which pair together to form base pairs (A-T and C-G). The sequence or order of these bases along the helix encodes genetic information. Genes are specific sequences of bases that contain the code necessary to form proteins in the body. They are the basic units of genetic inheritance and are structured to form chromosomes.

Depending on the subject of study, genetic tests are classified into three main types:

• Molecular tests: These analyze DNA fragments to determine the exact nucleotide sequence and identify gene mutations.
• Cytogenetic tests: These examine entire chromosomes to detect abnormalities in their number or structure.
• Biochemical tests: These do not analyze DNA itself but rather the proteins resulting from gene encoding. Variables such as size, quantity, or activity level are assessed.

When Are They Indicated?

Genetic tests are also classified according to the reason for which they are prescribed:

• Diagnostic tests: These confirm or rule out the presence of a genetic or chromosomal disorder. They are recommended when a person has symptoms compatible with a particular disorder.
• Predictive and presymptomatic tests: These are recommended when there is a family history of a genetic disease. They are performed before symptoms appear to identify associated genetic mutations and assess the risk of developing the disease.
• Carrier screening tests: These are recommended before having children to couples with a family history of recessive genetic disorders. The test confirms whether they carry a copy of the mutated gene, thus determining the risk of passing it on to their offspring. These tests are also suggested for individuals belonging to ethnic groups with a higher risk of certain genetic diseases.
• Prenatal diagnostic tests: These are conducted during pregnancy to detect anomalies in the fetus’s DNA.
• Newborn screening tests: These are performed on newborns within the first 72 hours of life. They are comprehensive studies that analyze genes associated with numerous genetic diseases.
• Preimplantation genetic testing: This is used in assisted reproduction procedures to detect genetic changes in embryos before their implantation in the uterus.
• Forensic genetic tests: These are not diagnostic tests but rather an identification method used to confirm a suspect’s identity in criminal investigations, establish biological relationships between individuals, or identify victims of a disaster or crime.

How Are They Performed?

To conduct a genetic study, a sample of the person’s genetic material must be examined. Various procedures can be used to collect the sample, including:

• Blood sample: Collected via needle puncture.
• Buccal swab: A swab or small brush is used to collect a sample from the inner cheek mucosa.
• Amniotic fluid sample: The amniotic fluid is aspirated through an abdominal puncture.
• Placental tissue sample: A sample of placental tissue is taken, either through an abdominal puncture or by inserting a catheter through the cervix.
• Hair analysis: The root of a hair is analyzed.

Once collected, the sample is studied in the laboratory, where different procedures are carried out depending on the specific genetic analysis required.

Risks

Blood sampling or buccal swabs pose no physical risk to the patient beyond the possibility of developing a small bruise in the case of blood extraction. However, some invasive prenatal tests carry a slight risk of miscarriage.

Genetic studies may also have significant emotional or social consequences due to their results, as they can involve diagnosing a serious illness, reconsidering a pregnancy, or even triggering family tensions.

Additionally, it is important to highlight the limitations of genetic testing. Even if a genetic mutation is detected, it is not always possible to predict with certainty whether the disease will develop or, if it does, how it will progress.

What to Expect from a Genetic Study

As mentioned, different procedures exist for conducting a genetic study. Once completed, a specialist will inform the patient of the results and possible courses of action based on them.

A positive result indicates a genetic alteration. Depending on the reason for the test, this may mean:

• The person has a genetic disorder. The diagnosis helps determine the most appropriate treatment plan.
• The person is a carrier of a specific genetic variant that can be passed on to their offspring. In this case, genetic counseling can help assess the risk of hereditary transmission and support informed family planning decisions.
• The presence of genes associated with a particular disease is confirmed. In some cases, this means the disease will develop in the future, while in others, it only signifies an increased risk. In both situations, an early intervention plan should be devised, whether to prevent disease onset or to begin appropriate treatment as soon as possible.

A negative result means no genetic alteration was found. However, it may be necessary to repeat the test later or conduct additional tests to confirm the negative result, as not all genetic changes associated with a specific disorder can always be detected.

Sometimes, results are inconclusive because they do not provide useful information. This can happen when variants of uncertain significance are found—DNA changes whose relationship with a disease has not been confirmed. In such cases, periodic follow-up testing may be required.

Specialties That Request Genetic Studies

Genetic tests are conducted within the medical specialty of medical genetics.