• Test Code:
    2050
  • Department:
    Molecular Genetics
  • Test Synonyms:
    DMDystrophica Myotonica 1Steinert DiseaseMyotonic Dystrophy
  • CPT Code(s):
    8140181404***New CPT Codes as of 01/01/2019***8123481239 if expanded
Background:

Myotonic dystrophy 1 is the most common form of inherited adult-onset muscular dystrophy.  Myotonic dystrophy is caused by the expansion of a CTG trinucleotide repeat that occurs in the 3’ untranslated region of the DMPK gene.  Inheritance is autosomal dominant and anticipation (early onset and more severe symptoms) occurs with the transmission of larger expansions in successive generations.  Three forms include mild, adult, and congenital.  Affected females are at risk for offspring with congenital myotonic dystrophy, characterized by severe hypotonia at birth and learning disabilities or mental retardation.

 Reasons for Referral:

  • Diagnostic testing in symptomatic patient to confirm diagnosis
  • Carrier testing in family
  • Prenatal testing when parent has expansion

Methodology:

PCR:  Normal and premutation sized alleles and smaller full mutations are detected by PCR analysis.

Southern analysis:  used to detect larger expansions.

Reference Range:

Phenotype

#CTG Repeats

Normal

5-35

Premutation

36-49

Affected (adult onset)

50-1000

Affected (congenital)

1000-2000 (in fetuses)

Specimen Requirements:

  • Blood: 6.0 mL EDTA (purple-top) or ACD (yellow-top) tube
  • DNA: 25µg at a minimum of 120ng/µL (DNA must be extracted in a CLIA-certified laboratory or a laboratory meeting equivalent requirements as determined by the CAP and/or CMS)
  • For prenatal or neonatal specimens, please call Client Services at (855) 535-1522.
  •  Prenatal:

    • Direct Amniotic Fluid (10-20mL)
    • Direct CVS
    • Cultured Amnio or CVS (2-T25 flasks)

    Notice Regarding Molecular Genetic Testing on CVS or Amniotic Fluid Specimens:

    • Maternal cell rule-out testing will be performed on all prenatal specimens received.Please provide maternal blood in addition to the fetal specimen.Additional charges apply for the maternal cell rule-out test.
    • All genetic testing performed on Direct CVS or Direct Amniotic Fluid specimens will be confirmed on cell cultures prepared by Knight Diagnostic Laboratories.Cell cultures will be prepared from the specimen received.Additional charges apply for confirmatory testing.
A REQUISITION FORM MUST ACCOMPANY ALL SAMPLES.  Please include detailed clinical information,  including ethnicity, clinical history, and family history.

Test Performed (Days):

Weekly

Turn Around Time:

14 – 21 Days

Shipment Sensitivity Requirements:

  • Package and ship specimen to remain cold, but not frozen. 
  • Ship via overnight express, using the FedEx priority overnight label provided. 
  • Contact Client Services for shipping kits and instructions at (855) 535-1522.

References:

Additional Info:

Genetic counseling is indicated for individuals with a family history of DM.