A: Whole-exome sequencing - Parker Core Knowledge

Understanding the Context

What Is Whole-Exome Sequencing?

Whole-exome sequencing is a laboratory technique that sequences all the protein-coding regions of the human genome—the exome—comprising about 1–2% of the entire genome but containing roughly 85% of known disease-causing mutations. Unlike whole-genome sequencing, which analyzes the full DNA sequence including non-coding regions, WES hominates on the exonic regions where most pathogenic variants are found.

This focused strategy allows researchers and clinicians to efficiently detect genetic changes such as single nucleotide variants (SNVs), insertions, deletions (indels), and splicing mutations—variants that often have direct functional consequences.

Key Insights

How Does Whole-Exome Sequencing Work?

The process of WES involves several key steps:

1. DNA Extraction: High-quality genomic DNA is obtained from a biological sample (blood, saliva, tissue).
   
2. Exome Enrichment: Using targeted capture kits, exonic regions are isolated by hybridization to probes that bind coding sequences.
   
3. Library Preparation & Sequencing: Enriched exonic DNA fragments are sequenced using high-throughput next-generation sequencing (NGS) platforms.
   
4. Bioinformatic Analysis: Raw sequencing data is aligned to a reference genome, variant calls are identified, and pathogenicity is predicted using databases and algorithms.
   
5. Variant Interpretation: Clinicians and geneticists interpret results to determine if identified variants are disease-causing, likely pathogenic, or of uncertain significance.

The precision and scalability of WES have revolutionized diagnostic capabilities in both clinical and research settings.

Final Thoughts

Key Applications of Whole-Exome Sequencing

1. Diagnosing Rare Genetic Disorders

Many rare diseases are rooted in single-gene mutations. Traditional diagnostic methods often fail to identify the cause, but WES dramatically improves diagnostic yield—sometimes reaching 50–70% diagnostic rates in pediatric patients with undiagnosed genetic conditions.

2. Cancer Genomics

In oncology, WES helps identify tumor-specific mutations, enabling targeted therapy selection and providing insights into tumor evolution and resistance mechanisms. It's increasingly used in hematologic malignancies and solid tumors alike.