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Test Code POLG2 SEQ POLG2 Sequencing

Clinical System Name

Polymerase Gamma 2 Sequencing Analysis Request

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.

 

 Testing is appropriate for individuals with progressive external opthalmoplegia with:

  • Multiple mtDNA deletions in skeletal muscle and/or
  • Cytochrome oxidase (COX)-deficient muscle fibers

Sample Requirements

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

Minimum: 10µg

Note: 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

 

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

 

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

Reference Range

Interpretive report will be provided

Methodology

Method: Bi-directional sequencing of all exons and exon-intron boundaries

 

Limitations: Mutations in the promoter region, large deletions, large duplications, or rare recombinant mutations may not be detected by this method.

CPT Codes

81406 (updated 1/20/16 by jconta)

Special Instructions

Links to:  POLG-Related Disorders GeneReview

Requisition

Molecular Genetics

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.