Genetic testing: who is it indicated for and what does it reveal?

Genetic testing is a medical study that looks for changes in genes, chromosomes, the genome, or associated molecular markers to confirm or rule out a suspected disease, assess hereditary risk, understand the likelihood of transmitting a disease to children, or help choose treatment strategies. This is fundamentally important: genetic testing is not synonymous with a single blood test, but rather a whole class of studies with different purposes and varying clinical value. [1]

In practice, it is prescribed in four main scenarios. The first is diagnostic, when a child or adult already has symptoms, congenital anomalies, developmental delays, neuromuscular manifestations, cardiomyopathy, hereditary forms of hearing loss, or other signs that suggest a hereditary disease. The second is prognostic and preventive, when it is necessary to determine whether the risk of disease is increased before the onset of symptoms. The third is reproductive, when the examination helps assess the risk of having a child with a hereditary pathology. The fourth is therapeutic, when genetic data helps select a drug, dose, or antitumor strategy. [2]

A crucial aspect of genetic testing is that it almost always affects not only the individual but also their family. Since DNA is shared by blood relatives, a pathogenic variant detected in one individual may have implications for parents, children, siblings, and other relatives. This is why modern sources emphasize the importance of pre- and post-test genetic counseling. This helps select the right person for initial testing and discuss the implications of the results for the family in advance. [3]

Genetic testing is not prescribed "just in case" without a clinical reason. It is most useful when the results can truly change the diagnosis, monitoring strategy, the scope of prophylaxis, treatment options, or reproductive decisions. If testing is performed without a well-thought-out goal, there is a high risk of receiving either an uninformative result or a variant of uncertain significance, which will only increase anxiety and prevent a clear course of action. [4]

It's important to understand the other side of the issue: genetic testing isn't omnipotent. Even a high-quality clinical test can't always predict whether a disease will develop, how severe it will be, or at what age symptoms will begin. For many conditions, the result reflects risk or probability, not a guaranteed future. Therefore, genetics should almost never be considered in isolation from clinical presentation, family history, and conventional medical data. [5]

Table 1. Main goals of genetic testing

Target	What helps to find out	Typical clinical situation
Diagnostic	Is there a hereditary cause for the existing symptoms?	Congenital anomalies, developmental delay, suspected monogenic disease
Prognostic	Is the risk of illness increased before symptoms appear?	Family history of hereditary cancer, cardiomyopathy, neurodegenerative disease
Carrier	Is the person a carrier of a variant that can be passed on to the child?	Planning a pregnancy
Prenatal	Does the fetus have signs of chromosomal or monogenic pathology?	High-risk pregnancy
Oncogenetic	Is there a hereditary predisposition to cancer?	Early cancer, multiple tumors, family history
Pharmacogenetic	Can genetics influence drug or dose choice?	Selection of therapy, risk of toxicity

The summary is based on materials from MedlinePlus, the US Centers for Disease Control and Prevention, the US National Cancer Institute, and the Clinical Pharmacogenetics Consortium. [6]

What types of genetic testing exist?

The simplest division is by the level of change searched. Molecular tests look for changes in a single variant, a single gene, a group of genes, or a very large volume of DNA. Chromosomal methods evaluate not individual DNA letters, but rather large rearrangements: extra or missing chromosomes, large deletions, duplications, and rearrangements of chromosomal regions. This is why "genetic analysis" can refer to fundamentally different technologies. [7]

Targeted testing for a known variant is used when a specific change has already been identified in a family and it is necessary to check whether another relative has inherited it. This is the narrowest and most targeted type of testing. It is useful when the clinical question is very specific, but is useless if the familial variant is unknown or if a disease with widespread genetic heterogeneity is suspected. [8]

Single-gene testing is used when the clinical picture is highly typical of a syndrome typically associated with a specific gene. A gene panel is used when the same phenotype can be caused by multiple genes. This approach is often used in epilepsy, cardiomyopathies, hereditary hearing loss, hereditary tumor syndromes, and other conditions where diagnostic uncertainty is high, but the range of most likely genes is already known. [9]

Exome sequencing and genome sequencing are broader methods. Exome sequencing primarily examines coding regions, where most known clinically significant alterations are located. Genome sequencing covers virtually all DNA and allows for a broader view, including some noncoding regions. These methods are particularly useful when a symptom complex does not fit into a single obvious syndrome or when previous, more specific tests have failed. [10]

However, broad-spectrum methods have limitations. Exome sequencing is generally less effective at detecting some deep intragenome alterations, methylation abnormalities, repeat expansions, and some copy number variants. The American College of Medical Genetics and Genomics guidelines specifically emphasize that in pediatrics for congenital anomalies, developmental delays, and intellectual disabilities, exome or genome sequencing should be considered a first- or second-line test, but the choice of method should still take into account the clinical context and limitations of the technology. [11]

Chromosomal methods remain important and have not been supplanted by sequencing. Karyotype helps identify large chromosomal rearrangements, while chromosomal microarray analysis identifies smaller deletions and duplications of DNA regions. Therefore, in modern practice, there is no universal "best test for everyone": sometimes a narrowly targeted analysis is needed, sometimes a panel, sometimes an exome, sometimes a genome, and sometimes a chromosomal method is needed. [12]

Table 2. What methods reveal what

Method	What is he looking for?	When it is especially useful	Main limitations
Analysis of a known family variant	1 specific change	Checking relatives	Not suitable for initial search for cause
Analysis of 1 gene	Changes in 1 gene	A very characteristic clinical syndrome	Narrow scope
Gene panel	Changes in a group of genes	Genetically heterogeneous diseases	May not cover a rare, unexpected gene
Exome sequencing	Coding regions of the genome	Unclear diagnosis, complex phenotype	Does not see some non-coding, methylation and repetitive changes
Genome sequencing	Almost all of the DNA	The broadest search	Complex interpretation, more secondary finds
Chromosomal method	Major chromosomal changes	Aneuploidies, major rearrangements, deletions, duplications	Doesn't see all the point options

The summary is based on MedlinePlus and the American College of Medical Genetics and Genomics guidelines. [13]

How genetic testing works in practice

Proper genetic testing begins not with a test tube, but with a clinical assessment. Before testing, a physician or genetic counselor collects a detailed personal and family history, evaluates the phenotype, constructs a pedigree, and formulates the question the test should answer. This step determines whether a specific test, a panel, exome sequencing, genome sequencing, or chromosome analysis is needed. [14]

The next step is pre-test counseling and informed consent. The patient should be explained what the test is looking for, what results are possible, what the test will not reveal, whether secondary findings will be analyzed, what the consequences may be for relatives, and what will happen after the results are received. This is especially important for broad-spectrum methods, as they may reveal clinically significant changes unrelated to the primary reason for referral. [15]

The sample itself is most often obtained from blood, saliva, or a swab from the inside of the cheek. In some cases, skin, amniotic fluid, chorionic villi, tumor tissue, or other materials are used. The type of sample depends not on convenience, but on the clinical need: for hereditary testing, sample from the person himself is usually needed, for prenatal diagnosis, sample from the fetus, and for somatic tumor testing, sample from the tumor. [16]

After collection, the sample is sent to a laboratory, where appropriate technology is used and the changes detected are then interpreted. For exome and genomic testing, family samples can increase diagnostic yield, especially if the child and both parents are tested. The American College of Medical Genetics and Genomics guidelines specifically note that trio testing typically yields higher diagnostic yield than testing only one patient. [17]

Post-test counseling is no less important than pre-test counseling. After receiving the results, it's important to explain whether they confirm the diagnosis, change treatment, affect the prognosis, whether relatives need testing, and whether there are grounds for a reinterpretation in a few years. Without this step, even a well-performed test can easily become a source of confusion and unnecessary anxiety. [18]

Table 3. What the examination route usually looks like

Stage	What's happening	Why is this necessary?
Clinical evaluation	Complaints, examination, family history, pedigree	Choose the right test
Pre-test counseling	Discussion of benefits, limitations, secondary findings, family implications	A conscious decision
Obtaining a sample	Blood, saliva, smear, tissue, prenatal material	Technical execution of the analysis
Laboratory research	Choice of method and interpretation	Search for clinically significant changes
Post-test counseling	Analysis of the results and action plan	Proper medical use of the answer
Family follow-up examination if necessary	Testing relatives	Clarification of risk and prevention

The summary is based on data from the US Centers for Disease Control and Prevention, the US National Cancer Institute, MedlinePlus, and the American College of Medical Genetics and Genomics. [19]

How to read the result and why a negative answer does not always mean there is no problem

Modern clinical genetics uses a five-tiered classification of variants: pathogenic, likely pathogenic, of uncertain clinical significance, likely benign, and benign. This system was created to standardize the findings of different laboratories and reduce arbitrary interpretations. It applies to results obtained from single-gene analysis, panels, exome sequencing, and genome sequencing. [20]

A pathogenic or likely pathogenic variant means that the laboratory has found a change that is highly likely associated with disease or disease risk. However, even this result does not always indicate a uniform course in all carriers. Manifestations are influenced by hereditary type, penetrance, variable expressivity, age, gender, environment, and other modifying factors. Therefore, the laboratory's conclusion must also be placed within the clinical context. [21]

There are two types of negative results. If a specific pathogenic variant was already known in the family, but it was not found in the person being tested, this is an informative true negative result. It does reduce the likelihood of a familial form of the disease in that person. However, if the familial variant was unknown and the test simply "found nothing," such a result may be an uninformative negative. It does not completely rule out a hereditary origin of the disease, as the cause may have remained beyond the scope of the test or may not yet be known to science. [22]

A variant of uncertain clinical significance is one of the most common and most misunderstood responses. It means that a change has been detected, but there is insufficient evidence to confidently classify it as either malignant or benign. This result, by itself, should not warrant major surgery, aggressive prophylaxis, or a definitive diagnosis. The US National Cancer Institute notes that such variants are often reclassified over time, often as benign. [23]

Broad-spectrum methods can yield secondary findings—clinically significant results unrelated to the primary reason for testing. Furthermore, old results sometimes require reinterpretation because knowledge about genes and variants changes over time. The American College of Medical Genetics and Genomics has issued a separate statement on the review and reanalysis of genomic results, emphasizing that a genetic report is not always a definitive, once-and-for-all document. [24]

Table 4. Understanding the Main Result Types

Result type	What does it mean?	What to do next
Pathogenic	Clinical significance has been proven	Correlate with the phenotype, adjust tactics, consider examination of relatives
Probably pathogenic	Very high probability of clinical significance	Use in a clinical context, sometimes supplemented by family examination
Of uncertain value	There is not enough evidence yet	Don't make radical conclusions, keep an eye out for possible reclassification
Probably benign	Most likely not related to the disease	Not usually used for diagnosis
Benign	Not related to disease	Does not require medical action

The summary is based on recommendations from the American College of Medical Genetics and Genomics and the National Cancer Institute. [25]

Limitations, risks and common mistakes

The first limitation is that genetic testing does not always answer all questions about a disease. It may reveal a predisposition, but it cannot predict whether symptoms will occur, how severe the disease will be, or whether the disease will progress quickly or slowly. This is especially important for preventive screening in adults and for conditions with incomplete penetrance. [26]

The second set of limitations is related to technology. Each method detects only its own class of alterations. A panel may miss an unexpected gene, an exome analysis may miss some non-coding and recurrent abnormalities, and chromosome analysis will miss many specific variants. Therefore, error often arises not in the laboratory, but rather at the stage of selecting the wrong method for the wrong question. [27]

The third block is psychological, family, and social consequences. MedlinePlus emphasizes that the risks of genetic testing are often associated not with the physical collection of samples, but with the emotional, social, and financial consequences of the results. People may experience anxiety, guilt, depression, fear for their children, and tension within the family, especially when the results affect blood relatives or fertility issues. [28]

Consumer self-testing kits remain a separate issue. The US Food and Drug Administration and MedlinePlus warn that such tests vary in evidence, do not always test for all relevant variants, may provide different information from one company to another, and should not replace clinical genetic testing. A negative result in such a kit does not rule out the risk of disease, and a positive result should not, by itself, be grounds for treatment. [29]

Finally, confidentiality and the potential misuse of genetic information must not be forgotten. Professional guidelines emphasize the importance of protecting autonomy, privacy, and confidentiality, and also warn of the risk of unfair discrimination. Therefore, before undergoing an examination, especially outside the regular medical system, it is important to carefully read the rules for data storage, transmission of results, and subsequent use of biomaterial. [30]

Table 5. Main limitations and risks of genetic testing

Problem	What is the risk?	How to reduce the risk
Incomplete answer	The test does not provide a diagnosis or prognosis.	Select a method based on the clinical task
Technological limitation	The method does not see the required class of changes	Discuss the choice of test with a geneticist
Emotional stress	Anxiety, guilt, family conflicts	Pre-test and post-test counseling
Misinterpretation	Erroneous medical decisions on an uncertain variant	Analyze the result only in a clinical context
Consumer kits	False confidence or unnecessary anxiety	Confirm significant findings with clinical testing
Privacy risks	Unwanted use of genetic data	Review the privacy policy and data storage rules

Summary based on MedlinePlus, the US Food and Drug Administration, and the position of the American College of Medical Genetics and Genomics.[31]

Special clinical situations where genetic testing is of particular importance

In reproductive medicine, it is important to distinguish between carrier testing, prenatal screening, and prenatal diagnosis. Carrier testing assesses the risk of transmitting a hereditary disease to a child. Current guidelines from the American College of Medical Genetics and Genomics have moved away from the old, strictly ethnic approach and propose a more universal carrier testing strategy for pregnant women and those planning a pregnancy. [32]

Noninvasive prenatal DNA testing is a screening, not a definitive diagnosis. It is useful for assessing the likelihood of a chromosomal abnormality, but a positive result must be confirmed by an invasive diagnostic test. The American College of Medical Genetics and Genomics guidelines specifically emphasize the importance of quality pre- and post-test counseling during this type of testing. [33]

In pediatrics, genetic testing is particularly important for congenital anomalies, developmental delays, intellectual disabilities, and a number of unclear syndromic conditions. For these groups, the American College of Medical Genetics and Genomics recommends exome or genome sequencing as a first- or second-line test, as it offers higher diagnostic yield and can lead to earlier termination of a lengthy diagnostic search. [34]

A separate area is neonatal screening. The US Health Resources and Services Administration emphasizes that newborn screening allows for the early detection of serious but treatable diseases, when treatment is most effective. This is not the same as a full genomic screening of every child, but rather an organized program for the early detection of conditions where timely treatment changes the outcome. [35]

In oncology, it's important to clearly distinguish between genetic and tumor testing. The US National Cancer Institute emphasizes that genetic risk analysis looks for changes inherited from parents, while tumor testing looks for somatic changes that arise in tumor cells during life. These two approaches may overlap, but they are not mutually exclusive and answer different clinical questions. [36]

Pharmacogenetic testing occupies a special place because it seeks not so much the cause of a disease as the characteristics of drug response. The Clinical Pharmacogenetics Consortium is developing recommendations on how to use known genetic results to select therapy, and the US Food and Drug Administration emphasizes that pharmacogenetic data can assist in choosing treatment strategies, dosages, and assessing the risk of toxicity, but only when combined with clinical information. [37]

Table 6. Where genetic testing is particularly useful

Clinical situation	What question does the examination address?	Key feature
Planning a pregnancy	Is there a risk of having a child with a hereditary disease?	Carrier examination
Pregnancy	Is there a high risk of chromosomal abnormalities in the fetus?	Screening and, if necessary, confirmatory diagnostics
Congenital anomalies and developmental delays in children	Is there a molecular cause for the symptoms?	Often exome or genome is needed
Neonatal period	Is there a serious but treatable disease that needs to be caught early?	Newborn screening
Suspected hereditary cancer	Is there a hereditary predisposition?	Blood or saliva testing
Already diagnosed with cancer	Are there tumor targets for treatment?	Tumor tissue testing
Selection of medications	Can genetics change drug choice or dosage?	Pharmacogenetics

The summary is based on recommendations from the American College of Medical Genetics and Genomics, the US National Cancer Institute, the US Health Resources and Services Administration, and the Clinical Pharmacogenetics Consortium.[38]

Conclusion

Genetic testing is not a "catch-all" test, but a tool for accurately answering a specific clinical question. Its usefulness is greatest when it's clear before the test what exactly is being looked for, the best method for doing it, and how the results will impact the future actions of the physician, patient, and family. [39]

Modern practice requires thinking not only about the test itself, but also about the process surrounding it: pre-test counseling, choosing the right method, informed consent, competent interpretation, assessing family consequences, and, if necessary, re-evaluating the results years later. It is this approach that distinguishes clinical genetics from the random "search for mutations." [40]

Frequently asked questions

Should everyone undergo genetic testing?
No. It is most useful when there are symptoms, a significant family history, reproductive goals, a suspected hereditary tumor syndrome, or a need to clarify treatment options. Without a clinical question, the likelihood of receiving an uninformative result is higher. [41]

Can a consumer self-test kit provide a diagnosis?
No. Such kits are not a substitute for clinical genetic testing. Significant results must be confirmed by a medical test, and a negative result does not rule out a hereditary risk if the test did not check for all important variants. [42]

Which is better: a gene panel, exome sequencing, or genome sequencing?
There is no single best method for all cases. For a very characteristic phenotype, analysis of a single gene or panel may be sufficient, while for a complex or unclear picture, exome sequencing or genome sequencing are more useful. The choice depends on the clinical objective and the limitations of each method. [43]

What does a variant of uncertain clinical significance mean?
It's a change for which there's insufficient evidence to determine whether it's pathogenic or benign. This response alone shouldn't be the basis for radical medical decisions. It may be reclassified over time. [44]

If the result is negative, does that mean there's no hereditary disease?
Not always. A true negative result is informative when a specific pathogenic variant is already known in the family. If the family cause is unknown, a negative test may be uninformative and not completely rule out a hereditary origin. [45]

Why is a consultation with a geneticist or genetic counselor recommended before testing?
Because it's during this consultation that the right person in the family is selected for the initial testing, the correct method, and the limitations, secondary findings, and implications for family members are discussed. This reduces the risk of an incorrect test and misinterpretation of the results. [46]

Is a noninvasive prenatal test a definitive diagnosis?
No. It's a screening test that assesses the likelihood of a pathology. A positive result requires confirmation by a diagnostic method. [47]

Can genetic testing help select a drug?
Yes, in some cases. Pharmacogenetic testing can provide insight into how a person metabolizes certain drugs and the risk of ineffectiveness or toxicity, but such results must be interpreted in conjunction with clinical data and current guidelines. [48]