Understanding Genomics

Understanding Genomics is a growing collection of evidence-based resources shaped by questions from individuals and families navigating genetic conditions, genetic testing, family history, and genomic information, as well as from healthcare professionals, researchers, and anyone interested in genetics and genomics.

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Some questions may be straightforward, while others relate to complex genetic conditions, testing, uncertainty, or scientific research. Every question helps us understand what people most need support to understand.

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Questions We Explore

Each month we explore selected questions to support understanding of genetics and genomics. Topics are developed from questions raised through our educational work, emerging research, and suggestions submitted through this website. All resources published on this page will remain freely available.

Coming on or around 2 November 2026: “What is the difference between genetic and genomic research?” and “How do scientists discover genes linked to disease?”

October 2026

  • In brief

    Genome sequencing is a way of reading the DNA sequence across most or all of a person's genome. It can be used to help identify genetic causes of health conditions, investigate cancer, support research and, in some circumstances, inform healthcare decisions. Because genome sequencing generates a large amount of information, however, identifying and interpreting medically relevant genetic variants can be complex.

    What is genome sequencing?

    Genome sequencing is a technique used to determine the order of the DNA bases, A, T, C and G, across a genome.

    Whole genome sequencing (WGS) aims to sequence the entire genome, including both protein-coding and non-coding regions. This makes it broader than tests that examine only particular genes or selected parts of the genome.

    One copy of the human genome (or 23 chromosomes) contains around 3 billion DNA bases (that is around 6 billion DNA bases when considering 23 pairs of chromosomes from both parents). Sequencing technologies do not usually read this entire sequence in one piece. Instead, DNA is broken into smaller fragments, which are sequenced in parallel. The resulting short sequences, known as reads, are then mapped to a reference genome using computational methods.

    The sequencing process therefore produces a large amount of data. Bioinformatics is used to process and analyse this information, helping identify genetic variants that may be relevant to the person's health or the question being investigated.

    How is genome sequencing different from other genetic tests?

    Genetic testing can examine different amounts or types of genetic information.

    Some tests focus on a single gene, while others examine a selected group of genes known to be associated with a particular condition. Whole exome sequencing focuses mainly on the protein-coding regions of genes, whereas WGS also includes non-coding regions.

    Because WGS examines a much broader portion of the genome, it can potentially detect a wider range of genetic variants in a single test. However, more information does not necessarily mean a clearer answer. The significance of many genetic variants remains uncertain, and not every part of the genome can currently be interpreted equally well.

    What is genome sequencing used for?

    Genome sequencing has a range of applications in healthcare and research.

    Diagnosing genetic conditions

    Genome sequencing can help investigate the genetic causes of rare or undiagnosed conditions, particularly when there are many possible genes that could be involved.

    Because WGS can examine many genes at the same time, it may identify a genetic change that would not have been considered through a more targeted test. A genetic diagnosis may help explain a person's condition and, where appropriate, inform further healthcare, family discussions or eligibility for particular treatments or clinical trials.

    Understanding cancer

    Cancer cells can acquire genetic changes that differ from those in the person's healthy cells.

    Sequencing can therefore be used to examine the genome of a tumour and identify genetic changes that may help explain how the cancer developed or how it behaves. In some situations, these findings may help inform treatment choices or eligibility for clinical trials.

    Genome sequencing can also identify genetic variants present in a person's constitutional or germline DNA that may indicate an inherited predisposition to cancer. This can have implications for the person and, potentially, their family members.

    Supporting research

    Genome sequencing is also an important research tool.

    Researchers can compare genome sequences from many people to investigate genetic causes of disease, discover previously unknown disease-associated variants and study patterns of genetic variation. In cancer research, sequencing can also help researchers investigate patterns of genetic changes within tumours.

    Genome sequencing can also be applied beyond human genetics, including the sequencing of infectious organisms to help identify and study pathogens.

    Does genome sequencing read and interpret everything in the genome?

    Not necessarily.

    Although whole genome sequencing generates sequence data across most of the genome, the data that are analysed depend on the purpose of the test and the clinical or research question.

    For example, in clinical practice, laboratories may use a virtual gene panel, analysing genes known to be relevant to a person's symptoms or suspected condition even though the person's whole genome has been sequenced.

    This means that having a whole genome sequenced does not necessarily mean that every genetic variant has been examined for every possible health condition.

    What are the limitations of genome sequencing?

    Genome sequencing can provide extensive information, but it cannot identify or explain every genetic condition.

    Some regions of the genome remain technically difficult to sequence or interpret. Certain types of genetic changes may require other testing methods, and some variants may be difficult to determine as disease-causing or harmless.

    Genome sequencing can also identify many genetic variants that are not known to cause disease. Distinguishing clinically relevant findings from the large amount of normal human genetic variation requires applying bioinformatics, interrogating genomic and biomedical databases, and drawing on expert interpretation.

    There may also be variants of uncertain significance or additional findings that were not directly related to the original reason for testing. These findings can require careful consideration in their clinical context.

    For these reasons, a genome sequence itself is not a diagnosis. The information needs to be analysed and interpreted alongside the person's clinical features, family history and other relevant information.

    Can genome sequencing be useful again in the future?

    Potentially, yes.

    One important feature of genome sequencing is that the underlying sequence data may contain information that becomes more useful as new genes, genetic variants and scientific knowledge are discovered.

    In some circumstances, previously generated genome data can therefore be reanalysed when a diagnosis was not initially identified or when new information becomes available. This means that a genome sequence may potentially provide value beyond the original analysis.

    However, whether and how genomic data are reanalysed depends on the testing service, clinical context and relevant policies.

    Key takeaway

    Genome sequencing provides a comprehensive way of examining a person's DNA, potentially allowing many genes and different types of genetic variation to be investigated at the same time. It is used in the diagnosis of genetic conditions, cancer investigation and research, among other applications.

    Generating a genome sequence does not automatically reveal which genetic variants are medically important. Bioinformatics, scientific evidence and clinical information are needed to analyse and interpret the findings. As genomic knowledge develops, previously generated data may also sometimes be revisited to look for information that could not be recognised previously.

    Further reading

    If you would like to learn more about genome sequencing and how genomic data are analysed, the following educational resources provide further information:

  • In brief

    People with the same genetic condition can experience different symptoms, severity or age of onset. Even people who carry the same disease-associated genetic variant may not be affected in exactly the same way.

    These differences can be influenced by other genetic variants, biological processes, and environmental or lifestyle factors. In some cases, a person who carries a disease-associated variant may not develop the associated condition at all. Understanding why this happens is an important area of genomic research.

    Does having the same genetic variant mean having the same condition?

    Not necessarily.

    A disease-associated genetic variant can have different effects in different people. One person who carries a particular variant may develop the associated condition, while another person carrying the same variant may remain unaffected.

    Even when two people both develop the condition, they may experience different symptoms, different levels of severity, or symptoms that begin at different ages.

    Two terms are commonly used to describe these differences:

    • Penetrance describes whether people who carry a particular disease-associated variant develop the associated condition.

    • Expressivity describes the extent or pattern in which the condition is expressed, such as the types or severity of symptoms.

    A condition may therefore have reduced or incomplete penetrance if some people who carry a disease-associated variant do not develop the condition. It may also show variable expressivity if people who develop the condition experience it in different ways.

    What can influence how a genetic condition develops?

    These factors may include:

    Genetic background and genetic modifiers

    People have many genetic variants throughout their genomes. Some of these can influence how other genes work or how biological pathways function, and may therefore modify the effects of a disease-associated variant.

    These variants or genetic factors are often described as genetic modifiers. They can help explain why the same disease-associated variant does not always have exactly the same effect in different people.

    Common genetic variation

    Some genetic modifiers are common genetic variants, which are widespread in the population, can also contribute to differences in disease risk and clinical features. Although each variant may have only a small effect on its own, many variants can collectively contribute to differences in disease risk and clinical features.

    For example, research has found that common genetic variation can influence the risk and clinical presentation of some conditions that are traditionally considered to be caused mainly by a single gene.

    A 2025 study of maturity-onset diabetes of the young (MODY) (see Further reading below) found that a person's wider genetic background, including common variants associated with type 2 diabetes, was associated with differences in the age at which diabetes developed and the severity of the condition.

    This does not mean that a condition previously described as a single-gene disorder is necessarily caused by many genes. Rather, common genetic variants can act as genetic modifiers, influencing how a disease-associated variant affects an individual.

    Gene regulation and other biological processes

    Genetic modifiers can also influence how genes are regulated and how cells function.

    Genes do not work in isolation. Their activity is influenced by regulatory mechanisms and by the biological environment within different cells and tissues. Genetic variants that affect these processes can therefore modify the effects of a disease-associated variant.

    For example, research published in 2026 (see Further reading below) found that genetic background surrounding a particular chromosomal deletion could influence gene regulation and cellular processes associated with differences in neurodevelopmental features. These findings provide further evidence that the effects of a genetic change can depend partly on the wider genetic and biological context in which it occurs.

    Together, these findings help researchers understand why the same genetic change can sometimes be associated with different outcomes between individuals.

    Environmental and lifestyle factors

    Environmental exposures, lifestyle and other aspects of a person's health can also influence how some genetic conditions develop or progress.

    Depending on the condition, factors such as diet, physical activity, smoking, infections, medications or other health conditions may contribute to differences between individuals. However, the importance of these factors varies considerably between conditions. They do not explain all differences in people with genetic conditions.

    Can someone carry a disease-associated variant without developing the condition?

    Yes.

    When some people who carry a disease-associated variant do not develop the associated condition, the variant is said to have reduced or incomplete penetrance.

    This does not necessarily mean that the variant is harmless. Instead, it means that carrying the variant does not always lead to the same outcome in every person.

    The likelihood of developing a condition can depend on the particular genetic variant, the person's wider genetic background, age and other biological or environmental factors.

    Can two people with the same genetic condition have different symptoms?

    Yes.

    When people with the same genetic condition experience different symptoms or different levels of severity, this can be described as variable expressivity.

    For example, one person may have relatively mild features while another person with the same condition may have more severe or additional features. Symptoms may also begin at different ages or affect different parts of the body.

    This variation can occur even between members of the same family who carry the same disease-associated variant.

    Why can't genetic information always predict exactly what will happen?

    Genetic information can provide important information about the likelihood of developing a condition and, in some circumstances, about its expected features. However, it does not always allow the exact outcome for an individual to be predicted.

    This is because the relationship between a genetic variant and a person's characteristics can involve multiple genetic, biological and environmental influences. Some of these influences are still not fully understood.

    Research into genetic modifiers and other factors that contribute to variable penetrance and expressivity is helping to explain this complexity. However, findings from studies of groups of people do not necessarily predict exactly how a condition will affect one particular individual.

    Key takeaway

    The same genetic condition does not necessarily affect everyone in the same way. Even people who carry the same disease-associated variant may differ in whether they develop the condition, which symptoms they experience, how severe those symptoms are and when they begin.

    These differences can be influenced by other genetic variants, biological processes, and environmental or lifestyle factors. Understanding these influences is an important part of genomic research and can help us better understand the relationship between genetic variation and human health.

    Further reading

    The resources below provide further information about genetic variation, genetic conditions and the factors that can influence how they affect individuals. They include accessible educational resources as well as examples of recent research discussed in this article.

September 2026

  • In brief

    Genetic risk describes the probability that a persona may carry a particular genetic variant or may develop a condition associated with genetic factors. How risk is estimated depends on the condition and the information available, which may include family history, clinical features, genetic test results and population data. For some single-gene conditions, risk can be estimated relatively clearly from patterns of inheritance. For many common conditions, however, risk reflects the combined influence of multiple genetic, lifestyle and environmental factors and can be more difficult to estimate precisely.

    How is genetic risk estimated?

    Genetic risk can be estimated using different approaches, depending on the condition and the question being considered. These may include established patterns of inheritance, family history, population data, genetic test results and clinical risk-prediction models.

    Statistical approaches can then be used to combine different pieces of information and estimate the likelihood of a particular outcome. For example, Bayesian analysis can be used to update an initial probability when additional information, such as family history or genetic test results, becomes available.

    The information used in a genetic risk assessment may include:

    • family history and the pattern of affected relatives across generations

    • the age at which relatives developed a condition

    • clinical features and medical history

    • results from genetic testing

    • genetic test results from other family members

    • population-based information

    • lifestyle and environmental factors, where relevant

    A well-recorded family history or genetic pedigree can therefore provide important information for risk assessment. Additional information, including genetic testing, may change an initial estimate and sometimes substantially improve its accuracy.

    Genetic risk for single-gene conditions

    Some genetic conditions are primarily caused by genetic variants in a single gene. There are often referred to as single-gene or Mendelian conditions.

    Where the inheritance pattern is well established, the pattern of affected and unaffected relatives in a family can provide useful information about the likelihood that a person carries a disease-causing variant or may develop the condition.

    For example, in some autosomal dominant conditions, a person who carries a disease-causing variant has a 50% chance of passing that variant to each child. In autosomal recessive conditions, risk depends on whether both parents carry disease-causing variants in the same gene.

    However, even in single-gene conditions, risk assessment may require more than simply following a pattern through a pedigree. Genetic test results, other non-genetic test results (such as biochemical test results), and information from other family members may all affect the assessment.

    What about conditions influenced by multiple genes?

    Many common health conditions do not follow a simple Mendelian pattern. They may be influenced by genetic variants across multiple genes, each contributing a relatively small amount to overall disease susceptibility, together with lifestyle, environmental and other factors.

    These are often described as polygenic or multifactorial conditions.

    Examples include high blood pressure, type 2 diabetes and coronary artery disease.

    For these conditions, having several affected relatives may suggest increased susceptibility, but the pattern usually cannot be explained by a single genetic variant being passed through the family. The same condition may also occur in people without a strong family history.

    Estimating risk for multifactorial conditions is therefore more complex. It may involve information from large populations, multiple genetic factors and relevant clinical, lifestyle and environmental information. The interactions between these factors can also make it difficult to predict an individual’s risk precisely.

    Can genetic risk estimates change?

    Yes. A genetic risk estimate is based on the information available at a particular point in time and may change as new information becomes available.

    This may include:

    • a new diagnosis in the family

    • additional information about the age or circumstances of a diagnosis

    • genetic testing of another family member

    • a new genetic test result

    • improved understanding of a particular genetic variant

    • updated population data or information about disease risk

    For this reason, a risk estimate should be understood in the context in which it was made. New evidence may refine the assessment.

    Does increased genetic risk mean I will develop a condition?

    Not necessarily. An increased genetic risk means that the probability may be higher than in a particular reference population or under a different set of circumstances. It does not necessarily mean that a condition will develop.

    Key takeaways

    Genetic risk is an estimate of probability, not a certainty. How that risk is assessed depends on the condition and the information available, such as family history, clinical features, genetic test results and population data. Risk can sometimes be estimate relatively clearly for single-gene conditions, while risk many common, multifactorial conditions is more complex and may involve a combination of genetic, lifestyle and environmental factors. Understanding how a risk estimate has been generated (and what information it does and does not include) can help put genetic information into context.

    Further reading

    If you would like to learn more about genetic inheritance and genetic risk assessment, the following educational resources provide further information:

  • In brief

    Genetic conditions can be inherited in different ways, depending on the gene or genes involved and how genetic variants are passed from one generation to the next. Common inheritance patterns include autosomal dominant, autosomal recessive, X-linked and mitochondrial inheritance. Some genetic changes arise for the first time in an individual rather than being inherited from a parent. Understanding the inheritance pattern can help explain how a condition may occur within a family and what it may mean for other family members.

    What does inheritance mean?

    Inheritance is the process by which genetic information is passed from parents to their children.

    Most of our cells contain two copies of most genes, with one copy inherited from each biological parent. Genetic variants can therefore sometimes be passed from one generation to the next.

    Whether a genetic condition is inherited, and the likelihood of it being passed to future generations, depends on which gene is involved, the type of genetic variant and how that gene is inherited.

    Not all genetic conditions are inherited. Some genetic variants arise for the first time in an individual. For example, this can occur during early development or later in life, and such variants may be present only in particular groups of cells (see “somatic variants” below for more information).

    What are the main inheritance patterns?

    Different genetic conditions follow different patterns of inheritance. The main patterns include autosomal dominant, autosomal recessive, X-linked and mitochondrial inheritance.

    Autosomal dominant inheritance

    In autosomal dominant conditions, a disease-causing variant in one copy of a gene can be sufficient to cause the condition.

    A person with the variant may have a 50% chance of passing it on to each child, regardless of the child’s sex.

    However, having a disease-causing variant does not always mean that a person will develop the associated condition or experience it to the same degree. This can depend on factors such as penetrance and variable expression.

    Autosomal recessive inheritance

    In autosomal recessive conditions, a disease-causing variant generally needs to be present in both copies of the relevant gene for the condition to develop.

    A person who has one disease-causing variant and one working copy of the gene is often described as a carrier. Carriers are often unaffected, but some carriers may have mild symptoms or an increased risk of certain health problems, depending on the particular condition and genetic variant.

    If both parents are carriers of disease-causing variants in the same gene, each pregnancy has:

    • a 25% chance of inheriting disease-causing variants from both parents

    • a 50% chance of inheriting one disease-causing variant and being a carrier

    • a 25% chance of inheriting neither disease-causing variant

    These probabilities apply to each pregnancy independently.

    X-linked inheritance

    Some genetic conditions are caused by variants in genes located on the X chromosome.

    Because people typically have two X chromosomes or one X chromosome and one Y chromosome, the effects of an X-linked genetic variant can differ depending on a person’s sex chromosome pattern (XX or XY).

    X-linked conditions can follow different patterns, including X-linked dominant and X-linked recessive inheritance. Because X-linked inheritance can be more complicated than a simple 50% calculation, the specific condition and family history need to be considered when assessing risk.

    For example, in an X-linked condition, an affected father does not pass his X chromosome to his sons, but he passes his X chromosome to all of his daughters.

    Mitochondrial inheritance

    Mitochondria are structures within cells that help produce energy. They contain a small amount of their own DNA, known as mitochondrial DNA (mtDNA).

    Mitochondrial conditions can be caused by variants in nuclear DNA or mitochondrial DNA. When a genetic condition is caused by a variant in mitochondrial DNA, the variant is inherited through the maternal line, because mothers pass their mitochondria and mitochondrial DNA to their children, whereas father do not.

    Therefore, an affected mother can pass the mitochondrial DNA variant to all of her children, both daughters and son, meaning that the associated condition can be inherited by all of her children.

    Can a genetic condition occur without being inherited?

    Yes.

    Some genetic variants arise de novo, meaning that they occur for the first time in an individual rather than being inherited from either parent.

    A de novo variant may arise in an egg or sperm cell, shortly after fertilisation, during early development, or later in life. If a variant arises in an egg or sperm cell, it may be passed on to the person’s children. In contrast, variants that arise after fertilisation or later in life may be present only in particular cells or tissues and are generally not passed on to children. In some situations, a person may therefore have a genetic condition even though there is no previous family history of the condition. See the “constitutional or germline variants” and “somatic variants” content below for more information.

    This is one reason why the absence of a family history does not necessarily rule out a genetic condition.

    Are all genetic variants present in every cell?

    No.

    Some genetic variants are present in every cell of the body because they are inherited or arise in the egg, sperm or germ cells. They are described as constitutional or germline variants.

    Other genetic variants develop during early development or later in life and may occur only in particular cells or tissues. They are known as somatic variants.

    Somatic variants are particularly important in cancer. Genetic changes can accumulate in cells as they divide and, in some circumstances, contribute to the development of a tumour.

    Somatic variants are not inherited from a parent and are not usually passed on to children.

    Why does the inheritance pattern matter?

    Understanding how a genetic condition is inherited can help healthcare professionals assess:

    • how a condition may have occurred within a family

    • whether other family members may have an increased chance of being affected or carrying a genetic variant

    • the likelihood that a genetic variant could be passed to future children

    • whether genetic testing may be appropriate for particular family members

    However, inheritance patterns do not always provide a complete explanation. Other clinical information, as well as individual’s lifestyle and environmental factors, may also be needed to understand an individual’s circumstances.

    Can inheritance patterns be complicated?

    Yes.

    Real families do not always follow simple textbook patterns. Factors such as new genetic variants, reduced penetrance, variable expression, genetic mosaicism, different variants in the same gene and interactions between genetic and environmental factors can make inheritance more difficult to interpret.

    For multifactorial conditions, there may not be a single inheritance pattern at all. Many genetic variants, together with lifestyle and environmental factors, may contribute to disease susceptibility.

    Key takeaway

    Genetic conditions can be inherited through different patterns, including autosomal dominant, autosomal recessive, X-linked and mitochondrial inheritance. Some genetic variants arise for the first time in an individual and may or may not be passed on to their children. Understanding the inheritance pattern can provide useful information about how a condition may occur within a family and what it may mean for other relatives, but other genetic, clinical and environmental information may also be needed to understand an individual’s circumstances.

    Further reading

    if you would like to learn more about genetic inheritance and how genetic variants can occur, the following educational resources provide further information:

August 2026

  • In brief

    A family history can provide useful clues about your health and may help healthcare professionals identify conditions that could have an inherited component. However, health conditions can result from a combination of genetic, lifestyle and environmental factors, and genetic disorders can occur in people with no known family history. Keeping an accurate family history, often recorded as a pedigree, can support discussions with your healthcare team and may become more informative as new information emerges over time.

    Why does family history matter?

    Your family history may provide useful clues about your health.

    Certain conditions occur more frequently in some families because of shared genetic factors. Others may be influenced by a combination of genetics, lifestyle and environmental factors.

    A family history is one source of information that healthcare professionals may consider alongside your own medical history, symptoms and, where appropriate, genetic testing to help guide clinical assessment and decision-making.

    However, having a family history of a condition does not necessarily mean you will develop that condition, and having no known family history does not necessarily rule it out.

    What information is usually helpful?

    When discussing family history, healthcare professionals often ask about relatives on both sides of the family, usually across three generations where possible.

    Helpful information may include:

    • date of birth or current age

    • family members who have had significant medical conditions

    • the age at which they were diagnosed

    • causes and ages of death, where known

    • pregnancy losses or stillbirths, when relevant to the clinical question

    • where known, lifestyle or environmental factors that may have contributed to a condition (for example, smoking, diet or physical activity)

    • the ethnic background of each side of your family

    You are not expected to know every detail. Even partial information can sometimes be helpful.

    Does a condition "run in the family" because it is inherited?

    Not necessarily.

    Some conditions are caused primarily by an inherited genetic variant. However, many health conditions—such as high blood pressure, type 2 diabetes and some cancers—develop through a combination of inherited genetic susceptibility together with lifestyle, environmental and age-related factors. As a result, several relatives may develop the same condition because they share genetic factors and/or aspects of their environment or lifestyle.

    A family history diagram, often called a pedigree, helps healthcare professionals identify patterns across generations and place medical conditions into the wider context of inherited, environmental and lifestyle influences. Where relevant, recording important lifestyle and environmental factors alongside medical conditions can further improve understanding of potential contributors to health.

    Because of this complexity, family history alone cannot determine whether a condition is inherited. Likewise, the absence of a known family history does not rule out a genetic condition. For example, some genetic disorders arise from new (de novo) genetic variants, which occur for the first time in an individual rather than being inherited from either parent.

    Can family history change over time?

    Yes. New diagnoses may arise or additional information may become available over time.

    Keeping a record of important diagnoses within your family can be helpful, particularly if new information emerges. Updating your family history periodically can help ensure it remains as accurate and informative as possible.

    How can I record my own family history?

    Recording your family history as a pedigree is a useful way to organise and maintain accurate family information. A pedigree is drawn using standardised symbols and connecting lines commonly used by healthcare professionals (see Further reading below).

    When creating a pedigree, begin with yourself and your siblings (including half-siblings where relevant), then record information for your parents' generation (including aunts, uncles, cousins, nieces and nephews where appropriate) and your grandparents' generation. Where possible, include the information described in the "What information is usually helpful?" section above.

    Store your pedigree safely and update it as new information becomes available. If your family history raises any concerns, discuss it with your healthcare team, who can consider it alongside your personal medical history and, where appropriate, arrange further assessment.

    Key takeaways

    A family history is an important part of understanding genetic and genomic information. It may provide useful clues that help healthcare professionals assess inherited conditions and guide decisions about further assessment, genetic testing or clinical management. Like any medical assessment tool, family history should always be considered alongside other relevant clinical information and evidence.

    Further reading

    If you would like to learn more about taking and recording a family history, the following educational resources provide further information on pedigrees and the standardised symbols and lines used by healthcare professionals, which you may use when drawing your own pedigree.

  • In brief

    Genetic testing may provide valuable information in some situations. The decision to have a genetic test depends on the question being asked, your personal and family history, and whether the results are likely to influence healthcare or personal decision-making. Understanding the potential benefits, limitations and implications of testing is an important first step.

    What is genetic testing?

    Genetic testing examines a person's DNA to look for genetic variants or changes that may help explain a health condition, identify an inherited disorder, or understand the potential risk of developing certain conditions.

    Different genetic tests are designed for different purposes. Some are used to diagnose a condition, while others help investigate inherited conditions within families, inform treatment decisions or identify whether someone carries a genetic variant that could be passed on to their children.

    When might genetic testing be considered?

    Genetic testing may be considered in a range of situations, for example:

    • when there is a strong family history of an inherited condition

    • when someone develops a condition at an unusually young age

    • when several relatives have experienced the same or related conditions

    • when a healthcare professional suspects an inherited disorder

    • to help guide treatment for some medical conditions, including certain cancers

    • during family planning in specific circumstances

    Not everyone with a family history requires genetic testing. Whether testing is appropriate depends on the individual's circumstances and the clinical question being considered.

    What are the potential benefits?

    Genetic testing may:

    • help explain the cause of a medical condition

    • help understand whether a condition is inherited and how this may affect other family members

    • help guide healthcare decisions or treatment in some situations

    • provide reassurance when an inherited condition is excluded, where appropriate

    The benefits vary depending on the type of test being performed and the question being investigated.

    What are the limitations?

    Genetic testing cannot answer every question.

    A negative result does not always rule out a genetic cause, and a positive result does not necessarily mean a person will develop a condition. Some results identify variants of uncertain significance (VUS) (see our July 2026 article below, “How are genetic variants classified in genetic testing, and can their interpretation change over time?”), where there is currently insufficient evidence to determine whether the variant contributes to disease.

    Some conditions also arise through a combination of genetic, lifestyle and environmental factors, meaning genetic testing alone may not provide a complete explanation.

    Understanding what a particular test can—and cannot—tell you is an important part of informed decision-making.

    What about direct-to-consumer genetic tests?

    Some companies offer genetic tests that can be purchased online, often without involving a healthcare provider.

    These tests may provide information about ancestry, traits or certain health-related genetic variants. However, the type of information provided, the scientific evidence supporting individual findings and the clinical usefulness of results can vary considerably between companies.

    Results from direct-to-consumer tests should not be used on their own to diagnose a medical condition or make healthcare decisions. If a result raises concerns, it is important to discuss it with your doctor, who may recommend further clinical assessment or confirmatory testing where appropriate.

    Questions to consider before testing

    Before deciding whether to have a genetic test, it may be helpful to ask:

    • What question am I hoping the test will answer?

    • What are the possible outcomes of the test?

    • What are the limitations of this particular test?

    • Could the results have implications for other family members?

    • Is treatment available to manage the condition or reduce the risk?

    • If I decide not to have the test, how might this affect my healthcare or future management?

    Key takeaway

    Genetic testing can be a valuable tool when used for the right purpose and interpreted in the appropriate clinical context. Understanding why a test is being offered, what it can and cannot tell you, and how the results may affect you and your family can help you make informed decisions.

    Further reading

    For readers interested in learning more, the following educational resources provide further information about genetic testing:

    Continue Exploring (Member Resource)

    Members can explore “Understanding genetic risk: what your DNA can and can’t tell you” and “Pharmacogenomics – how your genes may influence medication response” in greater depth within the Discern Genomics Member Portal. These materials expand on the scientific evidence, practical implications, and opportunities for further reflection.

July 2026

  • In brief

    A common genetic variant is a naturally occurring difference in human DNA. Most common variants are a normal part of human genetic diversity and help explain some of the biological characteristics that make each of us unique. A small proportion are associated with health and disease.

    Our DNA is remarkably similar

    Although every person is genetically unique, human DNA is remarkably similar. Around 99.6–99.9% of our DNA sequence is shared with other people, depending on the types of genetic differences included in the calculation. The remaining small proportion contains millions of genetic differences varying from person to person, known as genetic or genomic variants.

    What makes a variant "common"?

    Some genetic variants are found less frequently present or may be rare within a population, while others occur in many thousands or millions of people.

    Among the three main types of genomic variants—single nucleotide variants (SNVs, involving a difference in a single DNA letter or nucleotide), insertions and deletions (the addition or removal of typically fewer than 50 nucleotides), and structural variants (involving much larger changes to chromosomal regions)—SNVs are the most common type of genetic variant. If a single DNA letter change is present in at least 1% of a population, it is known as a single nucleotide polymorphism (SNP, pronounced "snip").

    Do common genetic variants cause disease?

    Most common variants have no impact on the function of a person’s genome and represent normal biological variation between people. For example, they may contribute to differences in height and skin pigmentation.

    Among the common variants that are associated with health and disease, they are usually only one part of a bigger picture. Lifestyle, environmental factors, and interactions with other genetic variants often play important roles.

    Why do scientists study common variants?

    Because common variants are shared across many people, they help researchers understand, for example:

    • genetic susceptibility to disease in a population

    • the shared and distinct biological pathways involved in human traits

    • how genetic, lifestyle and environmental factors interact to influence health

    Studying common variants has become an important part of modern genomic research and is helping improve our understanding of health and disease across populations.

    Key takeaway

    A common genetic variant is a naturally occurring DNA difference shared by many people. Most are a normal part of human genetic diversity, while some contribute—together with other genetic, lifestyle, and environmental factors—to differences in health and disease.

    Further reading

    For readers interested in learning more, the following external educational resources provide additional information on genomic variation:

  • In brief

    When a genetic test identifies a DNA variant, laboratories assess the available scientific evidence to determine whether that variant is associated with disease. Most clinical laboratories use a five-tier classification system ranging from benign to pathogenic. Sometimes there is not yet enough evidence to reach a clear conclusion, resulting in a Variant of Uncertain Significance (VUS). As scientific knowledge continues to grow, some variant classifications may be updated over time.

    How are genetic variants classified?

    Clinical laboratories evaluate multiple sources of evidence when interpreting genetic variants. These may include population studies, laboratory research, computer-based prediction tools, family studies, and information reported in scientific and clinical databases.

    Most laboratories follow internationally recognised guidelines developed by the American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology (AMP). In the UK, these principles are further refined by the Association for Clinical Genomic Science (ACGS) for clinical practice. The relevant ACMG/AMP and ACGS guidance documents are provided under "Further reading" below.

    Variants are usually classified into five categories:

    • Pathogenic – strong evidence that the variant causes disease.

    • Likely pathogenic – the evidence strongly suggests the variant causes disease, although a small degree of uncertainty remains.

    • Variant of Uncertain Significance (VUS) – current evidence is insufficient to determine whether the variant is disease-causing or harmless.

    • Likely benign – the evidence strongly suggests the variant does not cause disease.

    • Benign – strong evidence that the variant does not cause disease.

    What does "pathogenic" mean?

    A pathogenic variant is one for which there is strong scientific evidence that it causes a particular genetic condition.

    Importantly, a pathogenic classification does not necessarily mean that a person currently has a disease. Likewise, it does not necessarily determine whether symptoms will develop, when they will appear, or how severe they may become. The clinical impact of a pathogenic variant may depend on several factors, including the condition involved, the pattern of inheritance, age, environmental influences, and—in some cases—other genetic factors.

    What is a Variant of Uncertain Significance (VUS)?

    A VUS means that there is currently not enough evidence to determine whether the variant is associated with disease.

    A VUS is not a diagnosis, nor should it generally be used on its own to guide medical management. Instead, it indicates that additional research or clinical evidence is needed before the variant can be classified more confidently.

    As new information becomes available, such as:

    • studies involving larger populations,

    • laboratory research,

    • reports from other individuals with the same variant, or

    • additional family testing,

    the classification may become clearer over time.

    Can genetic test results change over time?

    For inherited (germline) genetic testing, the DNA sequence itself does not change, but our understanding of a genetic variant can.

    As scientific knowledge expands, some variants are reclassified to reflect new evidence. For example, a VUS may later be reclassified as likely pathogenic, pathogenic, likely benign, or benign. Reclassification between pathogenic or likely pathogenic and benign or likely benign categories is also possible, but such changes remain rare (see the publication by Kobayashi et al. listed under "Further reading").

    For this reason, a genetic test report should be interpreted as reflecting the best available evidence at the time it was issued.

    Why can classifications change?

    Advances in genomic research continue to improve our understanding of how genetic variants influence health and disease. New evidence may include:

    • larger and more diverse population databases;

    • functional laboratory studies;

    • improved understanding of disease mechanisms;

    • information from families with similar genetic findings; and

    • updated international interpretation guidelines.

    These developments help laboratories make more accurate variant interpretations over time.

    Key takeaway

    A genetic variant classification reflects the current scientific evidence, not absolute certainty. A pathogenic variant has strong evidence supporting its role in disease, while a Variant of Uncertain Significance indicates that more evidence is needed before a conclusion can be reached. As genomic research continues to advance, some variant classifications may change, allowing genetic variants to be interpreted with increasing confidence.

    Further reading

    If you would like to explore this topic in more detail, you may find the following evidence-based resources helpful:

    • Richards S, et al; ACMG Laboratory Quality Assurance Committee. Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. Genet Med. 2015;17(5):405-24. PMID: 25741868.

    • Manolio TA, et al. Opportunities, resources, and techniques for implementing genomics in clinical care. Lancet. 2019;394(10197):511-520. PMID: 31395439.

    • Durkie M, et al. ACGS Best Practice Guidelines for Variant Classification in Rare Disease 2024. ACGS Guidelines. [Accessed on 11/07/2026]

    • Kobayashi Y, et al. Clinical Variant Reclassification in Hereditary Disease Genetic Testing. JAMA Netw Open. 2024;7(11):e2444526. PMID: 39504018.

    Continue Exploring (Member Resource)

    Members can explore “Understanding Genetic Risk: What Your DNA Can and Can’t Tell You”, a related feature article, alongside additional learning resources through the Discern Genomics Member Portal. These materials build on the introduction provided here, exploring the scientific evidence in greater depth, considering practical implications, and providing opportunities for further reflection.

Help this resource develop

Understanding Genomics is a growing public resource launched in July 2026. It began with a small collection of research-informed educational resources and will continue to evolve in response to questions raised by individuals, families, healthcare professionals, researchers, and others interested in genetics and genomics.

Latest additions

October 2026

  • What is genome sequencing used for?

  • Why can the same genetic condition affect people differently?

Resource archive

September 2026

  • What does genetic risk mean?

  • How are genetic conditions inherited?

August 2026

  • How should I interpret my family history?

  • Should I consider genetic testing?

July 2026

  • What is a common genetic variant?

  • How are genetic variants classified in genetic testing, and can their interpretation change over time?

About this resource

This resource has been prepared by Discern Genomics to support public understanding of genetics and genomics. It is intended for educational and informational purposes only and does not provide medical advice, diagnosis, or treatment. Decisions relating to health, medications, or genetic testing should always be discussed with appropriately qualified healthcare professionals.

This resource reflects the scientific evidence available at the time of publication. As genomic research continues to evolve, future evidence may refine current understanding.

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