Whole Exome Sequencing (WES)

Definition:

Whole exome sequencing is a genomic technique that sequences all protein-coding regions (exons) of genes in a genome, known as the exome1. It captures approximately 1-2% of the human genome, containing about 85% of known disease-related variants.

Key Features:

• Sequences protein-coding regions of ~20,000 genes. 
• Covers ~1-2% of the genome. 
• More cost-effective than whole-genome sequencing. 
• Typically requires 4-5 Gb of sequencing per exome. 

Applications:

• Identifying disease-causing genetic variants. 
• Cancer research and diagnostics. 
• Rare disease diagnosis. 
• Population genetics studies. 
• Investigating alternative splicing events. 

Advantages:

• Cost-effective compared to whole-genome sequencing. 
• Focuses on regions most likely to affect phenotype. 
• Can identify coding variants across various applications. 
• Shorter turnaround time than whole-genome sequencing. 

Limitations:

• Does not cover non-coding regions. 
• May miss some disease-causing variants in introns. 
• Limited ability to detect certain types of structural variants. 

Process:

1. DNA library preparation. 
2. Exome capture using probes. 
3. High-throughput sequencing. 
4. Data analysis and variant calling. 

Clinical Relevance:

• Diagnostic tool for genetic disorders. 
• Identification of pharmacologically druggable alterations.
• Detection of cancer-related genetic aberrations. 

FAQs

1. How does WES differ from whole-genome sequencing?
   – WES focuses on protein-coding regions, while whole-genome sequencing covers the entire genome.
2. What is the diagnostic yield of WES?
   – Studies have shown diagnostic yields ranging from 25-50% depending on the condition and patient population. 
3. Can WES detect all types of genetic variants?
   – WES is best at detecting single nucleotide variants and small insertions/deletions, but may miss some larger structural variants. 
4. How long does WES analysis take?
   – The sequencing process can be done in as little as 1 day, but full analysis and interpretation can take several weeks. 
5. Is WES covered by insurance?
   – Coverage varies by provider and indication. Many insurers now cover WES for specific clinical scenarios.