When choosing between a gene panel and whole exome sequencing
A patient with multiple symptoms.
Sometimes overlapping clinical features.
Different diagnostic hypotheses are considered.
Each one pointing to a different group of genes.
Initial genetic tests may have already been performed.
Sometimes targeted.
Sometimes inconclusive.
At this stage, a decision becomes necessary:
→ should the analysis remain focused on a limited set of genes
or move toward a broader approach?
Gene panels are designed to investigate specific conditions.
Whole exome sequencing explores the coding regions more comprehensively.
Both approaches are valid.
But they serve different clinical situations.
In these situations, the difference does not lie in performing the test.
It lies in how the test is done from the beginning.
→ If this situation feels familiar, start the diagnostic pathway here.
Gene panel vs whole exome sequencing
A gene panel focuses on a predefined set of genes associated with a specific clinical suspicion.
It is used when the suspected condition is well defined and the margin for error is limited.
→ Whole exome sequencing (WES), instead, analyzes all protein-coding regions of the genome in a single test — approximately 20,000 genes.
In practice, the entire coding DNA is captured at once.
The difference is not only technical.
It reflects two different ways of approaching a diagnostic question:
→ starting from a specific hypothesis
→ or allowing the data to explore multiple possibilities at once
Both approaches are valid.
But they apply to different clinical situations.
A further distinction is important.
Some panels are targeted panels, where only a limited number of genes are sequenced.
Others are → exome-based panels, where sequencing is performed on the whole exome, but analysis is initially restricted to a selected group of genes.
This difference has practical consequences.
With exome-based panels, a negative result can be followed by an extension of the analysis to the entire exome — without repeating the sequencing.
With targeted panels, instead, a negative result often means restarting the process:
a new clinical evaluation, a new test, and additional time.
Coverage has traditionally been used as an argument in favor of targeted panels, since selected genes can be sequenced at higher depth.
Today, this distinction is essentially historical.
Modern WES technologies achieve coverage levels that are fully adequate for reliable detection of clinically relevant variants, even when compared to high-depth targeted panels.
When a gene panel is appropriate
A gene panel is appropriate when the clinical question is already well defined.
There is a clear diagnostic hypothesis,
the number of relevant genes is limited,
and the expected condition falls within a known and relatively narrow spectrum.
In these situations, a targeted approach may be efficient,
and a gene panel can provide a clear and timely answer.
However, choosing this pathway implies that the prescribing physician has a high level of expertise,
not only in the clinical aspects of the disease,
but also in its genetic heterogeneity,
its mutational spectrum,
and its current differential diagnosis.
Some targeted panels include genes related to differential diagnoses.
However, their composition is inherently limited by the time of their design
and may not include the most recently identified genes.
For this reason, the effectiveness of a panel also depends on how up-to-date the selected gene set is.
By contrast, exome-based panels offer a much higher degree of flexibility,
as the set of analyzed genes can be updated even shortly before the analysis.
Another relevant aspect is CNV detection.
With the adoption of next-generation sequencing, many analyses now include the identification of large deletions and duplications.
However, the reliability of CNV detection varies depending on the laboratory and the dataset used.
Laboratories performing whole exome sequencing typically analyze large numbers of samples using the same WES kit,
which allows more robust CNV detection through more consistent reference datasets.
Targeted panels, on the other hand, may rely on smaller datasets,
which can limit this aspect of the analysis.
When whole exome sequencing is preferred
Whole exome sequencing is preferred when the clinical situation cannot be reduced to a single, well-defined hypothesis.
Traditionally, this has referred to conditions such as isolated or syndromic intellectual disability.
However, its use is progressively expanding across multiple areas of medical genetics,
including retinal dystrophies, encephalopathies, and even less severe conditions such as non-obstructive male infertility,
as gene–disease knowledge continues to grow.
→ Clinical whole exome sequencing (WES) is therefore indicated when:
→ symptoms involve multiple systems
→ the clinical picture is atypical or evolving
→ previous tests have been negative or inconclusive
→ several different conditions could explain the presentation
A targeted panel assumes that the right question is already known.
But in many real clinical scenarios, this is precisely what is missing.
Whole exome sequencing may also be indicated even when the clinical suspicion appears well defined,
but the condition is characterized by extreme genetic heterogeneity or rarity,
making a targeted panel technically impractical or simply unavailable.
In all these situations, whole exome sequencing — and, in selected cases, → whole genome sequencing — makes the difference.
Instead of restricting the analysis to a predefined set of genes,
WES allows the case to be evaluated across the entire coding genome,
without committing in advance to a single hypothesis.
This does not mean “looking at everything” indiscriminately.
It means allowing different possibilities to be considered and integrated within a single analysis,
rather than explored sequentially through multiple tests.
Another key aspect is time.
When a panel is negative, the diagnostic process often needs to be restarted —
with a new hypothesis, a new test, and additional delay.
With whole exome sequencing, the entire coding genome is already available.
A negative result does not necessarily close the process,
but allows the analysis to be extended or revisited without repeating the sequencing.
This is also true for → exome-based panels,
where a negative result can be rapidly followed by a full exome analysis
on already acquired sequencing data.
Diagnostic implications
The choice between a gene panel and whole exome sequencing is not just technical.
It directly affects the probability of reaching a diagnosis.
A targeted panel can be highly effective —
but only if the initial hypothesis is correct.
When it is not, the result may be negative
not because the disease is absent,
but because it was not included in the test.
Whole exome sequencing does not guarantee a diagnosis.
But it reduces the risk of missing it
because the question was too narrowly defined.
The test does not simply generate data.
It defines the space in which the diagnosis can emerge.
Choosing the right approach
Defining how the diagnostic pathway is structured from the beginning directly impacts the effectiveness of the entire process.
A targeted panel may be appropriate when the clinical question is already clear and stable.
But when the situation is more complex,
starting with a narrow approach can lead to sequential testing,
longer timelines,
and delayed answers.
Whole exome sequencing, in these cases,
allows the diagnostic process to begin at a different level.
A practical compromise between effectiveness, cost, and step-wise readiness can be represented by exome-based panels,
which combine initial focus with the possibility of extending the analysis without repeating the sequencing.