- Whole Exome Sequencing (WES) is a powerful genomic technique that focuses on sequencing all protein-coding regions (exons) of genes in the genome. While these regions constitute only 1-2% of the human genome, they contain approximately 85% of known disease-causing variants, making WES a particularly valuable tool for clinical diagnostics and research.
- The process begins with careful sample preparation, where DNA is extracted from blood or tissue samples. This DNA is then fragmented into smaller pieces and prepared for sequencing through a series of steps including adapter ligation and exome capture. The capture process uses specific probes designed to hybridize with exonic regions, allowing for selective enrichment of these targeted areas. Library preparation follows, involving target enrichment, PCR amplification, and rigorous quality control measures to ensure optimal sequencing results.
- Sequencing is typically performed on next-generation sequencing platforms, generating reads of 100-150 base pairs in length. Most clinical applications aim for an average coverage depth of 100x to ensure accurate variant calling. The ability to multiplex samples makes the process more efficient and cost-effective. Following sequencing, the data undergoes extensive analysis, including quality control of raw reads, alignment to a reference genome, variant calling, annotation, and careful filtering to identify clinically relevant variations.
- WES has found numerous clinical applications, from rare disease diagnosis to cancer genomics and pharmacogenomics. It serves as a valuable tool in genetic counseling and research studies, offering a balanced approach between comprehensive genetic analysis and practical considerations. The technique’s cost-effectiveness compared to whole genome sequencing, combined with its focus on clinically relevant regions, makes it an attractive option for many applications. The reduced data storage requirements and relatively straightforward interpretation also contribute to its utility in clinical settings.
- Despite its advantages, WES does have certain limitations. The technique cannot detect variants in non-coding regions, which may also have biological significance. Some structural variants may be missed, and coverage can be uneven across different regions of the exome. Additionally, certain genomic regions remain difficult to sequence accurately due to their specific characteristics, such as high GC content or repetitive sequences. These limitations must be considered when choosing WES as a diagnostic or research tool.
