Pediatric Immunodeficiency VUS: Your Diagnostic Roadmap

The laboratory has identified a DNA change, yet the available evidence does not establish whether that change disrupts immune function, has no meaningful effect, or sits somewhere between those two possibilities.

For families and clinicians, this creates a diagnostic gap. A child may have recurrent infections, unusual inflammatory disease, persistent lymphopenia, poor vaccine responses, or another concerning clinical presentation, while the genetic report stops short of a molecular diagnosis. The appropriate response is not to treat the VUS as either proof or reassurance. Instead, we need a structured pediatric immunodeficiency VUS diagnostic pathway that connects the genetic result with immune phenotype, functional testing, family data, and time.

Inborn errors of immunity are more common than their historical reputation suggests. Their estimated incidence is approximately 1 in 1,666 individuals, and the International Union of Immunological Societies recognizes nearly 600 gene defects associated with these conditions. Yet genomic testing identifies a conclusive molecular diagnosis in only approximately 15–35% of suspected cases. A VUS is therefore not an unusual detour; it is a familiar part of the diagnostic landscape.

The diagnostic gap: why genetic testing often yields a VUS

Genetic sequencing is powerful, but it does not read disease from DNA in a simple one-to-one manner. It identifies differences in the genetic code. The clinical task is to determine whether a particular difference changes the immune cascade in a way that explains the child’s health history.

That determination depends on several forms of evidence:

• The clinical presentation: the pattern, severity, timing, and recurrence of infections; inflammatory or autoimmune features; growth and development; complications involving the lungs, gastrointestinal tract, skin, blood, or nervous system; and the response to vaccination.
• The gene-disease relationship: whether the affected gene is established as a cause of an inborn error of immunity and whether the suspected inheritance pattern fits the family.
• The variant itself: its location in the gene, its predicted effect on the resulting protein, how often it appears in population databases, and whether it has been observed in other affected individuals.
• Functional evidence: whether laboratory testing demonstrates a measurable disturbance in immune-cell development, protein expression, signaling, or cellular response.
• Family segregation: whether the variant tracks with disease or relevant immune features among biological relatives.
• Longitudinal evidence: whether the child’s immune phenotype evolves in a manner consistent with the suspected disorder.

A VUS means that the evidence is not yet sufficient for confident classification under established genetic interpretation frameworks. It does not mean that the laboratory has found the cause. It also does not mean that the finding is harmless. The result is best understood as a research and clinical lead that requires correlation.

This distinction is central to safe management. A VUS should not, by itself, confirm or exclude a diagnosis of primary immunodeficiency, now more commonly described within the broader group of inborn errors of immunity. Nor should a targeted therapy or gene-directed intervention be initiated solely because a VUS appears in a gene associated with immune disease.

A VUS is not a diagnosis waiting to be announced; it is a question that must be tested against the child’s immune phenotype.

The first practical step is to read the report in context rather than focusing only on the gene name. A result in a well-established immune gene may be clinically relevant, but the same result still requires evidence that the variant alters function and fits the child’s presentation. Conversely, a child may have a genuine immune disorder even when sequencing reports only a VUS—or no relevant variant at all.

Applying the ACMG framework to pediatric immune variants

Variant classification relies on guidance from the American College of Medical Genetics and Genomics, commonly referred to as the ACMG framework. This approach organizes evidence according to its strength and direction. The framework is not a substitute for clinical judgment; it is a disciplined way to prevent one striking but incomplete clue from dominating the interpretation.

In pediatric immunodeficiency, the most useful question is not simply whether a variant has been labeled a VUS. We should ask what evidence led to that classification and what type of evidence could reasonably change it.

Evidence that may move a variant toward pathogenicity

A variant may become more concerning when several independent findings align:

1. The gene and phenotype are concordant.

The child’s clinical presentation resembles the immune disorder known to result from disruption of that gene. This includes the type of infection susceptibility, age at onset, laboratory phenotype, associated inflammation, and pattern of organ involvement.

2. The inheritance pattern fits.

Some inborn errors of immunity follow autosomal recessive inheritance, while others may be autosomal dominant, X-linked, or associated with different mechanisms of transmission. A single heterozygous variant is not interpreted in the same way as two potentially relevant variants in a recessive condition.

3. The variant affects a biologically important region.

A change that alters a critical splice site, protein domain, or regulatory region may deserve closer attention, but prediction alone is not proof of disease causation. Computational tools can prioritize investigation; they cannot replace functional validation.

4. The variant is absent or very uncommon in population data.

A variant that is too frequent in the general population to account for a severe rare immune disorder becomes less plausible as the sole cause. Rarity, however, is not equivalent to pathogenicity.

5. The same variant has been observed in comparable clinical settings.

Published or curated cases can contribute evidence, but similarity must be examined carefully. A shared gene name does not guarantee that the variant produces the same mechanism or phenotype.

6. Functional testing demonstrates a relevant defect.

When an assay directly measures the biological process affected by the gene and shows a reproducible abnormality, the result can materially strengthen the interpretation.

Why a report may remain uncertain

A VUS often persists because the evidence is divided, limited, or difficult to compare. The variant may be rare but not functionally studied. The gene may be associated with a broad clinical spectrum. The child may be too young for the complete phenotype to emerge. Family members may not be available for testing, or the inheritance pattern may be unclear.

There can also be a mismatch between the test and the suspected disorder. A gene panel may not detect every type of structural change, repeat expansion, deep intronic alteration, regulatory variant, or complex genomic event. Exome and genome sequencing each have strengths and limitations, and a negative or inconclusive result does not necessarily close the diagnostic process.

The report should therefore be treated as a snapshot of current evidence. Classification may change as laboratories receive additional cases, functional studies become available, disease mechanisms are clarified, or the child’s clinical course provides new information. There is no universal standard timeframe for automatic VUS reclassification across all pediatric immunology centers, so families and clinicians should clarify how reinterpretation is handled by the testing laboratory and managing team.

A practical way to read the report

When reviewing pediatric genetic sequencing results, we can organize the discussion around five questions:

This conversation is more useful than asking whether the result is simply good or bad. A careful genetic counselor, clinical immunologist, and laboratory team should be able to explain the current classification, the limitations of the assay, and the specific evidence still missing.

Bridging the gap with functional immunological assays

Functional testing is often the bridge between a DNA finding and a clinically meaningful interpretation. In suspected inborn errors of immunity, these tests examine whether immune cells or proteins behave as expected. The appropriate assay depends on the gene, the suspected mechanism, the child’s age, current treatment, and the laboratory’s validated capabilities.

Flow cytometry is particularly important in pediatric immune diagnostics because it can evaluate several dimensions of immune-cell biology. Depending on the clinical question, testing may assess the number and distribution of immune-cell subsets, surface or intracellular protein expression, activation markers, signaling responses, or other measurable features of cellular function.

For a VUS, flow cytometry may help answer questions such as:

• Is the protein encoded by the affected gene present at the expected level?
• Is it correctly expressed on the relevant immune-cell population?
• Are specific lymphocyte or myeloid-cell compartments reduced, expanded, or developmentally abnormal?
• Does stimulation produce the expected signaling or activation response?
• Is the observed result reproducible and biologically consistent with the suspected condition?

The value of the assay depends on how directly it tests the mechanism. A general immune-cell count may show that something is abnormal, but it may not establish that the VUS is responsible. A more targeted assay that measures the affected pathway can be substantially more informative.

Choosing the right functional test

There is no single universal panel of functional immunological assays for VUS interpretation. Testing should be selected gene by gene and phenotype by phenotype. Depending on the suspected disorder, the management pathway may include:

• lymphocyte subset analysis;
• assessment of immunoglobulin levels and vaccine-specific antibody responses;
• neutrophil function studies;
• evaluation of cytokine production;
• receptor or protein-expression studies;
• phosphorylation or intracellular signaling assays;
• cellular proliferation after stimulation;
• complement-related testing;
• specialized assays performed in a research or referral laboratory.

The interpretation must account for pre-analytic and clinical variables. Acute infection, immunomodulatory medication, corticosteroids, recent vaccination, age-related immune differences, and sample handling can all influence results. A borderline or abnormal result may need confirmation under appropriate conditions.

We should also be precise about what functional testing can and cannot do. A normal assay does not automatically prove that the VUS is benign, particularly if the test does not capture the relevant mechanism or if the child’s phenotype is evolving. An abnormal assay may support pathogenicity, but it must still be interpreted alongside inheritance, clinical findings, and the known biology of the gene.

Why pediatric flow cytometry requires clinical context

Children do not have static immune systems. Reference ranges vary with age, and the distribution of immune-cell subsets changes during infancy, childhood, and adolescence. A result that appears reduced when compared with an adult reference interval may be appropriate for a young child, while a subtle abnormality may be significant when considered alongside recurrent infections and impaired vaccine responses.

This is why flow cytometry in pediatrics is not simply a matter of counting cells. The laboratory must use age-appropriate references and report the findings in relation to the clinical question. The immunologist then integrates the result with the immune phenotype, infection history, family history, and genetic data.

When the suspected gene affects protein expression or a defined signaling pathway, functional validation may provide the evidence needed to move a variant out of uncertainty. When the mechanism is less accessible to routine clinical testing, the most responsible conclusion may remain provisional, with ongoing surveillance and periodic review.

Family segregation studies: useful evidence, not a verdict

Family testing can make a VUS more interpretable by showing how it is distributed among relatives. In a suspected recessive condition, testing may reveal whether two variants are located on different copies of the gene, a configuration known as being in trans. In a suspected dominant condition, the presence or absence of the variant in affected or unaffected relatives may provide additional evidence.

However, segregation results must be interpreted with care. A relative may carry a variant without developing the full condition because of variable expression, age-dependent disease, incomplete penetrance, or a milder phenotype. An apparently unaffected parent may simply be too young to show features that emerge later. Conversely, a family member may have relevant immune abnormalities that were never recognized because their clinical presentation was subtle.

Family studies are therefore most informative when they include more than a genetic result. We may also need to review infection patterns, blood counts, immunoglobulins, vaccine responses, inflammatory symptoms, autoimmune disease, and other relevant clinical information. Testing relatives without a clear interpretive plan can create additional uncertain findings without resolving the original question.

When family testing is especially valuable

Segregation analysis is often worth discussing when:

• the suspected inheritance pattern is known and the family structure allows a meaningful comparison;
• there are two variants in a gene associated with a recessive immune disorder;
• a parent or sibling has a similar or unexplained immune phenotype;
• a variant appears de novo, meaning it is not detected in either biological parent;
• the result could affect reproductive counseling or evaluation of siblings;
• the laboratory has specified that family data would contribute to classification.

The goal is not to label relatives based on a single uncertain finding. The goal is to clarify whether the variant behaves in a way that supports the suspected disease mechanism.

Family testing is most helpful when it answers a defined biological question; broader testing without a plan can multiply uncertainty rather than reduce it.

Re-analysis: allowing the diagnosis to mature with the evidence

Genomic interpretation changes because genomic knowledge changes. New disease genes are described, existing gene-disease relationships are refined, population databases become larger, and functional studies may clarify variants that were previously poorly understood. A child’s own clinical history also becomes more informative over time.

Periodic re-analysis should therefore be considered part of the diagnostic pathway, especially when the initial testing produced a VUS and the clinical suspicion remains meaningful. Re-analysis is not the same as repeating the blood draw. In many cases, the original sequencing data can be reviewed against updated databases, classifications, and clinical information, although the available process varies by laboratory.

A productive re-analysis request includes:

• the original genetic report and test methodology;
• updated clinical features since the initial test;
• new immune laboratory results;
• results of functional assays;
• relevant family testing;
• changes in treatment or infection pattern;
• any new diagnosis in the child or close relatives.

The timing should be individualized rather than driven by a universal schedule. If the child develops a new clinical feature, if a relative receives a related diagnosis, or if a functional assay becomes available, re-analysis may be appropriate sooner. Otherwise, the immunology and genetics teams may recommend review as part of scheduled follow-up.

The question should also extend beyond the original VUS. If the initial test was limited—for example, to a targeted panel—and the clinical presentation remains unexplained, the team may consider whether broader sequencing or a different genomic method is justified. That decision depends on the original test’s coverage, the suspected biology, the child’s phenotype, and the likely clinical value of obtaining additional information.

Clinical decision-making without definitive molecular confirmation

A child does not need a confirmed gene defect before clinicians can manage a clinically significant immune problem. Medical decisions should be based on the child’s actual immune function and health risks, not on the presence of a VUS alone.

The management pathway may include monitoring for infection, assessing organ involvement, evaluating vaccine responses, treating documented infections promptly, and considering preventive strategies when the clinical picture supports them. Some children require closer pulmonary surveillance, immunoglobulin assessment, nutritional support, or coordinated care across infectious disease, hematology, pulmonology, gastroenterology, rheumatology, or other specialties.

The exact plan depends on the phenotype. A child with recurrent bacterial respiratory infections and impaired antibody responses raises different questions from a child with severe viral infections, persistent lymphopenia, invasive fungal disease, autoinflammation, or unexplained cytopenias. The VUS may help prioritize testing, but it does not replace this clinical distinction.

What a VUS should not trigger on its own

A VUS should not independently lead to:

• a definitive diagnosis being recorded without clinical and functional support;
• irreversible treatment decisions based only on the gene label;
• targeted therapy chosen solely because the gene is associated with an immune disorder;
• gene alteration treatment without evidence that the specific variant is pathogenic and clinically relevant;
• unnecessary restrictions for siblings or relatives who have not been appropriately evaluated;
• reassurance that ends follow-up when the child’s clinical presentation remains concerning.

At the same time, uncertainty should not become an excuse for inaction. If the immune phenotype is significant, we can treat the documented problem while continuing to investigate its cause. This parallel approach is often the most protective for quality of life: address current infection risk and organ health, while keeping the diagnostic work active.

Communicating uncertainty with families

Families need language that is accurate without being alarming. We can explain that the test found a genetic change, but current evidence cannot determine whether it affects immune function. We can then describe what information may help: immune-cell studies, functional validation, testing of relatives, broader clinical assessment, or future re-analysis.

It is also helpful to define what the result means for relatives. A VUS generally should not be used as a stand-alone basis for predictive testing or major medical decisions in otherwise healthy family members. If a sibling has concerning symptoms, evaluation should be guided by that child’s clinical presentation and immune testing, with genetics incorporated into the broader assessment.

Documentation matters. The report, laboratory contact information, family studies, functional assay results, and updated clinical summary should remain accessible. If care changes between institutions, this record prevents the diagnostic process from restarting at the beginning.

Building a durable diagnostic roadmap

A pediatric immunodeficiency VUS diagnostic pathway works best when each step produces a clearer question for the next one:

1. Confirm the clinical concern.

Establish whether the child’s infections, inflammation, laboratory abnormalities, or vaccine responses suggest an inborn error of immunity and identify the dominant immune phenotype.

2. Review the genetic result in detail.

Examine the gene, inheritance model, variant type, test limitations, classification evidence, and whether the finding is compatible with the child’s presentation.

3. Select a mechanism-based functional assay.

Use flow cytometry or another validated test when it directly evaluates the affected immune-cell population, protein, or signaling pathway.

4. Use family segregation strategically.

Test relatives when the results can address inheritance, phasing, de novo occurrence, or a shared phenotype.

5. Continue clinical management independently of the VUS.

Treat documented immune dysfunction and monitor complications according to the child’s actual risks.

6. Revisit the genomic data.

Request periodic re-analysis when new clinical, functional, family, or scientific evidence could change interpretation.

7. Reassess the testing strategy if needed.

If the phenotype remains unexplained, consider whether the original test could have missed a relevant genomic change or whether another diagnostic method is appropriate.

This is not a linear process in every child. A functional result may prompt family testing; a new infection pattern may change the clinical phenotype; a laboratory may reclassify the variant before any additional testing is completed. The roadmap is designed to keep those developments connected rather than treating each result as an isolated event.

Long-term outlook: uncertainty can still be managed well

A VUS can prolong the search for a molecular diagnosis, but it does not prevent thoughtful medical care. The long-term outlook depends much more on the child’s immune function, disease severity, organ involvement, response to management, and access to coordinated follow-up than on the uncertain label itself.

Some variants will eventually be reclassified as pathogenic or likely pathogenic when functional and clinical evidence accumulates. Others will move toward benign interpretations. Many may remain unresolved, particularly when the gene-disease relationship is complex or the relevant biological assay is not available. In each situation, the clinical plan should remain anchored to measurable health outcomes: reducing serious infections, protecting organ function, supporting development, and preserving quality of life.

The most constructive approach is neither to overinterpret the VUS nor to dismiss it. We use it as one piece of evidence within a wider diagnostic framework, combining clinical presentation, immune testing, functional immunological assays, family data, and updated genomic interpretation. That is how uncertainty becomes manageable—and how a difficult genetic result can still contribute to a safe, evidence-based path forward.