Image: AI-generated illustration of a genetics laboratory; not a photograph of an actual patient or test.
A genetic test can help explain symptoms, identify a carrier state, estimate some health risks or guide cancer treatment. But a report is not a prediction of everything that will happen to you. Its meaning depends on the question asked, the test used and your medical and family history.
What is genetics?
Genetics is the study of genes, inheritance and variation. DNA is the molecule that stores biological instructions, written using four chemical “letters”: A, C, G and T. Genes are stretches of DNA that help cells make functional products, including proteins. Chromosomes package DNA; most human body cells have 23 pairs. We usually inherit one chromosome of each pair from each biological parent. Mitochondria also contain a small amount of DNA.
Genes influence health alongside age, environment, exposures and other factors. Having a genetic risk factor does not always mean that a disease will develop.
Inherited, new and somatic changes: what is the difference?
Inherited or germline variants pass through an egg or sperm and are usually present throughout the body. Inherited disorders include cystic fibrosis and sickle cell disease. Many such conditions follow recessive inheritance, meaning disease usually requires relevant variants in both copies of a gene. Other conditions follow dominant, X-linked or mitochondrial patterns. The inheritance pattern matters when interpreting a result and discussing relatives’ risks.
De novo means newly arising. A change can occur in an egg, sperm or very early embryo without being inherited from a parent who carries it throughout their body. Such a constitutional change can cause a genetic condition despite no family history, and may be passed to the affected person’s children.
Somatic variants arise after conception in cells other than egg or sperm cells. They can occur during development or later life. Some contribute to cancer or noncancerous conditions. Many cause no illness: a somatic mutation does not automatically mean cancer.
Mosaicism means different groups of cells have different genetic makeup. Its effects depend partly on which tissues carry the change. A change confined to body cells is not passed through reproduction, but involvement of egg or sperm cells can affect inheritance risk.
What are mutations, and what types exist?
A mutation is a change in DNA. Reports often use the neutral term variant, because a DNA difference is not necessarily harmful.
Common descriptions include:
- Substitution: one DNA letter replaces another. A missense change alters a protein building block; a nonsense change introduces an early stop signal. A synonymous, sometimes called “silent,” change leaves the protein building block unchanged, although some affect how a gene works.
- Insertion or deletion: DNA letters are added or removed. Within a protein-coding sequence, a change whose length is not a multiple of three generally causes a frameshift, changing how later letters are read. An in-frame change preserves that grouping but may still matter.
- Splice variant: affects how RNA is processed before a protein is made.
- Copy-number change: a DNA segment is missing or present in extra copies.
- Chromosomal change: an extra or missing chromosome, or a rearrangement of chromosome material.
- Repeat expansion: an unusually increased number of repetitions of a DNA sequence, as in certain neurological conditions.
The type of change alone does not establish its medical significance.
Why might a clinician recommend testing?
Testing may help with:
- Diagnosis: investigating symptoms or a suspected genetic condition.
- Carrier testing: identifying variants that may matter for reproductive planning.
- Predictive or presymptomatic testing: assessing a particular future disease risk before symptoms appear.
- Cancer treatment: identifying tumor changes that may help select treatment or a clinical trial.
For example, a harmful BRCA1 or BRCA2 variant can increase cancer risk, but it does not mean a person definitely has or will develop cancer.
Samples can include blood, saliva, cheek cells or tissue. The sample alone does not tell you the test’s purpose. A blood sample might be used for constitutional testing or, in a different test, to look for tumor-derived DNA. Tumor testing and inherited-risk testing answer different questions. A tumor finding may need separate constitutional testing before conclusions are drawn about inheritance.
What is next-generation sequencing, or NGS?
NGS reads many DNA fragments in parallel. Computers assemble or compare the resulting sequences with a reference, and laboratories assess potentially relevant differences.
NGS can support:
- Gene panels: selected genes relevant to a clinical question.
- Exome sequencing: mainly the protein-coding portions of genes.
- Genome sequencing: a much broader view of coding and noncoding DNA.
The same technology can investigate constitutional conditions or tumor changes, but sample choice, analysis and interpretation differ.
Broader sequencing is not automatically the best test, and “whole genome” does not mean every possible abnormality will be detected or understood. Coverage varies. Depending on the assay, repeat expansions, copy-number changes, rearrangements and low-level mosaicism may need additional methods. Ask what the laboratory’s test can reliably find.
For more on how NGS can help guide cancer treatment, read Precision Oncology: How a Tumor’s Biology Can Guide Treatment.
How to read your genetic test report
Start with the reason for testing, sample, genes or regions assessed, main conclusion and limitations. Then review the details with the ordering clinician or a genetic counselor.
A report may show a gene name, the exact variant, a reference sequence and technical notation. “c.” commonly describes a coding-DNA change; “p.” describes a protein-level change. Heterozygous usually means one of two copies carries the variant; homozygous means both do. These labels describe the result, not its seriousness.
Constitutional reports commonly use five classifications:
- Pathogenic: evidence supports a disease-causing role.
- Likely pathogenic: strong evidence supports that role, although uncertainty remains.
- Variant of uncertain significance, or VUS: available evidence cannot establish whether the variant causes disease.
- Likely benign: evidence favors no disease-causing role.
- Benign: evidence supports no disease-causing role.
Even a pathogenic finding must fit the condition, inheritance pattern and clinical circumstances. A carrier finding is not the same as a diagnosis of the associated recessive disorder.
A VUS is not a diagnosis and should not, by itself, drive treatment, preventive surgery or other medical decisions. Care can still be guided by symptoms and personal or family history. Ask whether later reinterpretation or carefully selected family testing would help; classifications can change as evidence grows.
A negative result means no reportable finding was identified within the test’s scope. It does not exclude every genetic condition or erase a concerning family history. Sometimes a targeted negative result for a known family variant is informative; an unexplained negative result can leave the original question unresolved.
Tumor reports may use different evidence tiers and discuss treatment relevance. A listed drug or trial is not a guarantee of eligibility or benefit. Your oncology team must assess the cancer type, evidence and clinical situation.
Before and after testing
Discuss costs, turnaround time and what decisions the result might change. Ask about unexpected findings unrelated to the original question, which additional findings the laboratory actively looks for, and what choices you have about receiving them.
Results can matter to relatives and can bring emotional uncertainty. Genetic counseling can help explain options without directing you toward a particular personal choice.
Ask who can access your sample and data, how long they are stored and whether research use is optional. Privacy and insurance protections vary by country and jurisdiction. In the United States, GINA has important protections but does not cover life, disability or long-term-care insurance. Avoid posting identifiable reports or raw genetic data publicly.
Useful questions at your follow-up appointment include:
- Does this result explain my symptoms, indicate carrier status or change a risk estimate?
- Does anything need confirmation, and should my care change now?
- What could this test have missed?
- Should relatives seek counseling or targeted testing?
- Who should I contact about future reclassification or reanalysis?
The most useful genetic report is one interpreted in context, with a clear explanation of what it shows, what remains uncertain and what to do next.
This article provides general education and does not replace individualized medical advice or genetic counseling.
Sources and further reading
- MedlinePlus: What is genetic testing?
- MedlinePlus: Gene variants and how they occur
- MedlinePlus: Types of gene variants
- MedlinePlus: Understanding genetic test results
- NCI: Genetic testing for inherited cancer risk
- NCI: Next-generation sequencing
- NHGRI: Genome sequencing primer
- ACMG/AMP: Standards for interpreting sequence variants
- AMP/ASCO/CAP: Interpreting sequence variants in cancer
- NHGRI: Genetic discrimination and legal protections
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