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Useful For
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Whole Exome Sequencing (WES) analyzes the protein-coding regions (exomes) of the genome, which comprise approximately 1-2% of the human genetic material but harbor about 85% of disease-related mutations. WES facilitates the identification of genetic variants associated with rare or undiagnosed conditions, thereby supporting clinical diagnosis and informing treatment strategies. This approach is particularly valuable in diagnosing rare genetic disorders, such as intellectual disability, developmental delays, and congenital anomalies, by pinpointing mutations linked to specific conditions. Additionally, WES can identify inherited mutations that elevate cancer risk, enabling the implementation of proactive interventions and personalized therapeutic plans.
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Method name and description
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Method name: Whole Exome Sequencing
Description:
The process of Whole Exome Sequencing describes through several precise and interconnected stages. It begins with collecting a blood specimen from which genomic DNA (gDNA) is extracted.
The next key stage is library preparation. This process involves preparing the gDNA for sequencing by breaking it into smaller fragments and attaching short, specialized sequences known as adapters. These adapters serve as molecular barcodes, enabling the identification and amplification of each DNA fragment during sequencing.
Following this, exome capture is performed using hybridization techniques. In this context, hybridization refers to the use of engineered, single-stranded pieces of DNA called probes, which are designed to specifically bind to and "capture" the protein-coding regions (Exome) of the genome. This selective process enriches the sample for the most clinically relevant sequences, leaving out the vast non-coding regions.
After capturing the desired exonic DNA, high-throughput sequencing technology is used to read the genetic code of these fragments. The vast amount of data generated then undergoes sophisticated bioinformatics analysis to identify genetic variants potentially linked to rare diseases, inherited disorders, or increased cancer risk.
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Clinical information
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Whole Exome Sequencing (WES) is a powerful diagnostic tool primarily used to identify genetic causes of rare and inherited disorders, as well as to assess cancer risk. By selectively sequencing the protein-coding regions of the genome, WES enables the detection of single nucleotide variants—these are changes in a single building block of DNA that can sometimes cause disease. It can also find small insertions and deletions, and other alterations that may impact gene function.
WES is indicated for patients with unexplained developmental delays, congenital anomalies, suspected monogenic diseases (conditions caused by changes in a single gene), or inherited cancer syndromes. In addition to its diagnostic value for individuals, WES may also be utilized for carrier screening in couples who are planning a pregnancy, helping to assess the risk of passing on genetic disorders to their offspring. This can be especially beneficial for couples with a family history of genetic disease or those from populations with an increased prevalence of consanguinity.
However, WES may not detect all genetic changes. For example, it might not find variants that occur outside the coding (exome) regions of genes or large structural changes in DNA, so results should be interpreted with these limitations in mind. Interpretation of results requires thorough clinical correlation and may reveal both pathogenic and incidental findings, which should be reviewed in consultation with a genetic counselor or clinical genetics specialist.
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Aliases
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Whole Exome Sequencing
WES
Next Generation Sequencing
NGS
Genetic Testing
Trio analysis
Inherited disorder
Inherited Cancer
Gene Panel
Family Study
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Specimen type / Specimen volume / Specimen container
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Specimen Type
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Specimen Volume
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Container/Tube
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Whole Blood
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Adult: minimum 3 mL
Child : minimum 1ml
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Lavender top (EDTA)
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DNA
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minimum 2-3 µg
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2ml sterile cryovial
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Collection instructions / Special Precautions / Timing of collection
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Note: This is a "one-time " test. This means that the test is typically performed once and does not need to be repeated unless there are specific circumstances or changes in health status that warrant it.
Patient Preparation: Previous allogeneic bone marrow transplant can yield discordant leukocyte DNA; note clearly in clinical details.
Specimen Type: Whole blood or DNA from CAP/ISO or similar accredited laboratories is acceptable.
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Specimen Type
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Container/Tube
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Volume Required
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Patient Preparation / Notes
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Whole Blood (EDTA)
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Lavender-top EDTA tube
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Adult: ≥3 mL Child: ≥1 mL
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No fasting required. Note prior bone marrow transplant or transfusion.
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Extracted DNA
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Sterile microcentrifuge tube
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≥50 ng/µL concentration; minimum 20 µL
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DNA must be from patient’s own tissue; provide extraction method if from external lab
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Relevant clinical information to be provided
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Submit With Order
- Clinical indication and relevant history
- Family history
- Document prior allogeneic bone marrow transplant (may confound results).
Genetic counseling and informed consent are required
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Storage and transport instructions
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The specimens should be transported to Central Processing (CP) in the Qatar Rehabilitation Institute (QRI), 3rd floor, HBK MC in cool box with ice pack.
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Specimen Type
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Container/Tube
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Volume Required
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Storage Before Transport
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Transport
Conditions
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Whole Blood (EDTA)
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Lavender-top EDTA tube
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Adult: ≥3 mL Child: ≥1 mL
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Room temperature ≤24h; 2–8 °C preferred if delay expected
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2–8 °C (refrigerated), upright, avoid shaking; ≤72 hours
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Extracted DNA
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Sterile microcentrifuge tube
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≥50 ng/µL concentration; minimum 20 µL
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–20 °C or lower for long-term storage
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2–8 °C (preferred) or Room Temp ≤5 days if stabilized;
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Specimen Rejection Criteria
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Specimens will be rejected under the following conditions:
- Referral from departments other than HMC Medical Genetic department
- Wrong specimen container.
- Leaking or contaminated container.
- Unlabeled specimen.
- Mislabeled specimen.
- Improperly filled request form.
- No specimen types.
- No physician stamps.
- No clinical history/data documented.
- No request/electronic order received.
- Excessive hemolysis or clotted blood.
- Specimen received with wrong date and time.
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Biological reference intervals and clinical decision values
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An interpretive report will be provided.
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Turnaround time / Days and times test performed / Specimen retention time
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Turn Around Time
90 days Working Days from the date of sample receipt at DGD.
Routine : Sunday to Thursday (07:00 AM- 03:00 PM)
Specimen Retention Time
Whole Blood: Aliquots stored >2 years (if available)
Extracted DNA: Lifetime
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