PYGM SEQUENCING FOR GSD V - FULL GENE
Label Name: PYGM GSDV
Lab Discipline: Molecular Diagnostics
Institution:  Duke University Health System 
EAP ID:  LAB7736 
Last Review:  3/27/2017 10:42:35 PM
Specimen Type
  Blood
Container & Volume
  Age Group   Container   Volume  
  0  - 18 Years LAVENDER TOP TUBE 2  ML
Label Reminders
  Be sure to include patient's name, history #, date and time of collection, and collector's initials.
Collection Notes
  All:
  • Peripheral Blood: One lavender-top EDTA tube (minimum of 3 mls) is required for testing. Forward unprocessed peripheral blood promptly to the laboratory at ambient temperatures. THE SPECIMEN CANNOT BE FROZEN. GREEN-TOP (HEPARIN) TUBES ARE NOT ACCEPTABLE FOR TESTING.

    Amniocytes: 2-4ml of amniotic fluid is required. Forward promptly at ambient temperature only. Contact the Laboratory for additional information and instructions on sample requirements and shipping instructions. SPECIMEN CANNOT BE FROZEN.

    Cultured amniocytes / fibroblasts: Please contact the Laboratory for sample requirements and shipping instructions.
 
Transport
  Please deliver to lab at ambient temperature. If there is a delay of more than 24 hours in delivery, please refrigerate the sample. DO NOT FREEZE!
Turn Around Time -  Routine: 28 days   Stat: N/A
Reference Values


PYGM GSDV



No Reference Values
Methodology
  This assay uses PCR amplification followed by Sanger DNA sequencing to detect mutations in the PYGM gene that cause glycogen storage disease type V (GSD V). The coding sequences and flanking intronic sequences (minimum of 20 base pairs) of the PYGM gene are amplified from purified genomic DNA by PCR. The primers used in the PCR reactions contain M13 universal primer “tails” at their 5’ends, and have 3’ ends that are homologous to their genomic target sequence. The resulting PCR products are treated with an exonuclease/phosphatase mixture to remove excess PCR primers and nucleotides. These purified DNA amplicons are then sequenced using universal M13 forward and reverse primers and the Big Dye Terminator v3.1 Cycle Sequencing Kit (Applied Biosystems). These products are then purified with the Big Dye XTerminator Purification Kit (Applied Biosystems) and resolved using the ABI 3130xl Genetic Analyzer. Data is analyzed using the ABI Data Collection software v3.0, Sequencing Analysis software v5.4 and SeqScape software v2.6. Sequences are compared to the reference DNA sequence (GenBank Accession: NT_167190.1; NM_005609.2).

This test was developed and its performance characteristics determined by Duke Clinical Molecular Diagnostic Laboratory. It has not been cleared or approved by the U.S. Food and Drug Administration. This test is used for clinical purposes. It should not be regarded as investigational or for research. This laboratory is certified under the Clinical Laboratory Improvement Amendments of 1988 ("CLIA") as qualified to perform high complexity clinical testing.
   
Special Information
  All:
  • Additional Patient Information Required: Due to the unique nature of genetic testing, patients offered this test should receive pre-test and post-test genetic counseling. Counseling should help the patient understand the strengths and limitations of DNA testing and the medical implications for the patient as well as for other family members. Patients are also required to give consent for testing.
 
   
Clinical Significance and Interpretive Data
    McArdle disease (GSD Type V)is inherited in an autosomal recessive manner, mostly manifesting in the second or third decade of life with an estimated incidence of 1/100,000 live births. GSDV is caused by mutations in the PYGM gene. This 20 exon, 2529bp gene is located on the long arm of chromosome 11 and encodes for the protein myophosphorylase. Individual who carry two mutant copies of the PYGM gene generally have symptoms of GSDV. Heterozygous individuals (individuals with one mutant copy of the PYGM gene and one non-mutant copy) are generally asymptomatic. However, several cases have been reported in which a patient who has symptoms of GSDV harbors only one identifiable mutation. There is no clear correlation between specific mutations and the severity of disease. Two mutations in the GSDV gene are more common than other; the p.Arg50X mutation (32-85% of all mutations) and the p.Gly205Ser mutation (9-10% of all mutations).
   
Indications
    Patients who may benefit from testing include:

1. Patients with clinical symptoms consistent with GSD V including exercise intolerance, rapid fatigue, myalgia, cramping in exercising muscles which can be relieved after a few minutes of rest. These symptoms usually begin in the 2nd or 3rd decades of life. In rare instances, GSDV can manifest shortly after birth as a severe and rapidly progressive disease.

2. Patients with laboratory findings consistent with GSDV including deficient PYGM enzyme activity, elevated serum CK levels at rest, myoglobinuria,.

3.Patients with a family history of GSD V should be tested.

4. In cases of known familial mutations, amniocytes from an at-risk pregnancy may also be tested.
   
Limitations
    The sensitivity of DNA sequencing is high for the detection of nucleotide base changes and small deletions and insertions in the regions analyzed. Only the coding regions of the PyGM gene and immediate flanking intronic sequences are examined. Changes in the promoter region, farther into the introns, or in other non-coding regions of the gene, would not be detected. Mutations in genes other than PYGM would not be identified. Large deletions, duplications, multiple exon insertions, sequence alterations adversely affected primer binding, and complete deletion of one allele may not be identified using these methods.

Due to the limited number of studies in patients with glycogen storage disease (GSD) type V, the percentage of disease-causing alleles detectable by full gene sequencing is unknown.

The result from this testing are not intended to be used as sole criteria for clinical diagnosis or patient management decisions and are not a substitute for a physician's judgment and clinical experience. Correlation with other laboratory testing or clinical findings is required.
   
Test Synonyms
  Synonym(s): Glycogen Storage Disease type V
Synonym(s): GSD V
Molecular Diagnostics Laboratory
(MDX)

Medical Director:
 Michael Datto, M.D., Ph.D.
 Phone: 919-684-6965
 Email: michael.datto@duke.edu
Lab Director:
 Catherine Rehder Ph.D, FACMG
 Phone: 919-613-8434
 Email: catherine.rehder@duke.edu
Lab Director:
 Siby Sebastian Ph.D., DABMG
 Phone: 919-613-8432
 Email: siby.s@duke.edu

Address: 
 Wadsworth Bldg, Cytogenetics, Rm 0220
 2351 Erwin Rd
 Durham,  NC  27705
 Phone: 919-684-2698
 FAX: 919-668-5424

Performing Times: