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HelpTest Code LAB1891 POLG2 Sequencing
Clinical System Name
Polymerase Gamma 2 (POLG2) Sequencing
Description
Mutations in POLG2 lead to a failure to enhance the DNA-binding strength which stalls the DNA replication fork causing mtDNA deletions to arise. The progressive accumulation of the mtDNA deletions causes cytochrome c oxidase (COX) deficiency in muscle fibers, primarily external eye muscles and skeletal muscle.
Full gene sequencing is appropriate for individuals with progressive external opthalmoplegia with:
- Multiple mtDNA deletions in skeletal muscle and/or
- Cytochrome oxidase (COX)-deficient muscle fibers
Also available: Targeted Gene Variant Sequencing (LAB1915) - For targeted analysis of variants previously identified through clinical testing of a family member or research testing of the individual. Please review requirements and restrictions for testing.
Sample Requirements
Note: For patients who have had a whole blood transfusion, wait 10 days post transfusion to draw for genetic testing. No wait time is necessary for blood or saliva collection if the patient received leuko-reduced red cells or plasma.
Specimen: Whole blood, cord blood
Container(s): Lavender/EDTA, Yellow/ACD A or B
Preferred Vol: 3 mL
Minimum Vol: 1 mL
Note: Heparin samples (Green tops) are unacceptable.
Specimen: Extracted DNA from EDTA blood
Minimum: 10µg
Note: Isolation of nucleic acids for clinical testing must be performed in a CLIA-certified
laboratory or a laboratory meeting equivalent requirements as determined by the CAP
and/or the CMS. DNA concentration minimum 50 µg/mL; 260/280 ratio 1.70-2.00.
Specimen: Cultured cells
Acceptable: Fibroblasts
Container(s): T-25 flasks
Preferred Vol: 2 flasks
Specimen: Saliva collected using Oragene Dx OGD-575/675 collection kit.
Container: Oragene Dx OGD-575/675 collection kit
IMPORTANT NOTE: Manufacturer instructions must be followed. The Oragene Dx OGD575/675 kit is not for children under 6 months. Contact Lab Client Services for more information or to obtain a kit 206-987-2617, labclientservices@seattlechildrens.org
Processing Instructions
Reject due to: Heparin
Spin: No
Aliquot: No
Temp: Refrigerate
Storage location: Molecular Genetics box in CPA refrigerator #2
Off-site collection: Refrigerate blood samples until ready to ship. Transport all sample types at room temperature via overnight shipping.
Stability
| Specimen Type | Temperature | Time |
|---|---|---|
| Cultured cells | Room temp | 3 days |
| Whole blood, extracted DNA | Room temp | 3-5 days |
| Whole blood, extracted DNA | Refrigerated | 7 days |
| Extracted DNA | Frozen | ok |
| Saliva, ORAgene Dx OGD-575/675 | Room Temp | 2 weeks |
Note: Whole blood samples > 7days may be submitted to be assessed by our lab for acceptability for testing.
Availability
| STAT | Performed | TAT |
|---|---|---|
| Contact lab | Monday - Friday | 2-3 weeks |
Performing Laboratory
Seattle Children's Laboratory
Department
Department: Molecular Genetics Laboratory
Phone: 206-987-3872
Lab Client Services: 206-987-2617
Lab Genetic Counselor: LabGC@seattlechildrens.org
CPT Codes
| POLG2 full gene seq | 81406 |
| POLG2 targeted variant analysis | 81403 |
Methodology
Method:
Full gene seq: bi-directional sequencing of all exons and exon-intron boundaries
Targeted variant sequencing: bi-directional sequencing of targeted variant(s)
Limitations: Mutations in the promoter region, large deletions, large duplications, or rare recombinant mutations may not be detected by this method.
Reference Range
Interpretive report will be provided
Requisition
Special Instructions
Links to: POLG-Related Disorders GeneReview
Clinical Utility
DNA polymerase gamma is the only DNA polymerase found in the mitochondria and is responsible for maintaining the integrity of the mitochondrial genome by mtDNA replication and repair. DNA polymerase gamma is composed of a catalytic subunit (POLG1) and an accessory subunit (POLG2). POLG2 enhances the affinity of the DNA polymerase gamma to bind to DNA. Mutations in POLG2 lead to a failure to enhance the DNA-binding strength which stalls the DNA replication fork causing mtDNA deletions to arise. The progressive accumulation of the mtDNA deletions causes cytochrome c oxidase (COX) deficiency in muscle fibers, primarily external eye muscles and skeletal muscle. Autosomal dominant progressive external ophthalmoplegia with mtDNA deletions (PEO4) is characterized by adult-onset weakness of the external eye muscles (leading to ptosis), mild weakness of facial muscles and exercise intolerance.