Genetic testing · BEGINNER LESSON
Whole-exome sequencing
Whole-exome sequencing (WES) is a laboratory test that sequences the protein-coding parts of nuclear genes, called exons, to look for genetic variants. It uses next-generation sequencing methods to help identify disease-related changes, but it does not capture every kind of DNA change.
What it is and what it measures
Whole-exome sequencing (WES) measures the DNA sequence of the exome, which is the set of all protein-coding nuclear genes. In practice, the test looks for sequence differences, called variants, by comparing a person’s DNA reads to a reference genome or reference exome. A read is the short DNA sequence produced by the sequencing machine. WES is an untargeted next-generation sequencing (NGS) approach, meaning it examines many coding regions at once rather than only a few selected genes. [2,0]
[3] Educational Materials — Genetic Testing: Current Approaches [1] Whole-Exome Sequencing for the Identification of Genetic Factors ...
How it works
To do WES, the lab first enriches the DNA pieces that come from exons, then sequences them. Coverage and read depth matter because each nucleotide should be sequenced enough times to support a reliable call; coverage means how much of the exome is sequenced at a chosen minimum depth, and read depth means how many times a nucleotide is read. Paired-end reads sequence both ends of a DNA fragment and can align more clearly than single-end reads, especially in repetitive regions. [2]
[3] Educational Materials — Genetic Testing: Current Approaches
Why it is useful
WES can help diagnose previously undiagnosed people and can also be used in research to find genetic factors linked to disease. In reviewed studies of previously healthy patients with severe bacterial infections, WES helped identify inborn errors of immunity and also suggested new gene-disease associations. This shows why WES is valuable when the cause may lie in coding regions across many genes rather than in one preselected gene. [0]
[1] Whole-Exome Sequencing for the Identification of Genetic Factors ...
Limitations
WES does not reliably detect every genetic change. It can miss large copy number variants, some repeat expansions, balanced chromosome rearrangements, methylation defects, and some supernumerary chromosomes. Some regions are harder to sequence because of high or low GC content, and read-depth differences can also create false positives. Sequencing artifacts, uneven coverage, and batch effects can further complicate interpretation. [2,0]
[3] Educational Materials — Genetic Testing: Current Approaches [1] Whole-Exome Sequencing for the Identification of Genetic Factors ...
Interpreting results carefully
Many variants are found in each person, but not all are relevant to the trait being studied. Because many human genomes share background variation, labs must filter and prioritize candidates and use quality controls before making claims about disease causation. The reviewed studies also noted that strict prioritization rules are needed, because even a plausible variant is not automatically the cause of disease. [0]
[1] Whole-Exome Sequencing for the Identification of Genetic Factors ...
SEE THE IDEA
How whole-exome sequencing is used
Patient DNA is extracted for testing.
Exons are captured so coding regions are emphasized.
The machine produces many short reads from the enriched DNA.
Reads are compared with a reference to find candidate variants that may matter.
The steps move from sample preparation to data generation to interpretation.
WES focuses on coding DNA, then uses read quality and filtering to separate possible disease-related variants from background variation.
TRY IT YOURSELF
Test your understanding
Choose an answer, then check the explanation.
PUT IT TOGETHER
Match each concept to its meaning
Drag a label onto its description, or select a label and then select a description. This also works with a keyboard.
4 pairs to match
Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.