Getting Technical: Whole Exome Sequencing
We took some time to ask Priyanka, a Genetic Lab Techie working within the field of IVF, to talk us through Whole Exome Sequencing. Here is what she had to say:
The human “exome” consists of all the genome’s exons, which are the protein coding regions of the genes. This represents less than 2% of the genome, but contains nearly 85% of known disease-related variants. Whole-exome sequencing is a widely used next-generation sequencing method for sequencing all of the protein-coding regions of the genes in a genome. Exome sequencing can efficiently identify coding variants across a broad range of applications, including population genetics, genetic disease, and cancer studies.
Carrier testing has also gained popularity by using the technique of exome sequencing which involves testing to identify an asymptomatic adult who is a carrier for autosomal-recessive or X-linked recessive conditions. The testing is usually initiated on the basis of family history or because a genetic condition is common among individuals of the patient’s ethnicity.
What’s The Process?
Usually blood is collected from the patients and sent to the genetic laboratory. At the laboratory, DNA extraction from the blood samples is performed to proceed with the downstream processes. The library preparation involves a series of steps which prepares the samples for exome sequencing. Firstly, the genomic DNA undergoes a process called ‘Tagmentation’ which simultaneously fragments and tags genomic DNA with adapter sequences. Further the purified tagmented DNA is amplified in addition to, adding index adapters and sequences required for cluster amplification using a PCR program. Secondly, samples are pooled into one tube and hybridization with probes is performed, followed by binding targeted regions of DNA with capture probes. This hybridization and capture step is performed twice to ensure high specificity of captured regions. Finally, the enriched sample library is PCR amplified, undergoes QC check and loaded on to the NextSeq 500 Illumina platform for Exome sequencing. Once the exome sequencing run is complete, the data is forwarded to the bioinformaticians where data goes through a pipeline using various software to identify disease-related variants.
Exome sequencing is an opportunity to help educate other family members about potential risk. Taking time to learn about health and diseases that run in your family is worth it. It will help you understand your own health and make healthy choices.
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