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:
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Phenotype
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#CTG Repeats
|
|
Normal
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5-35
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Premutation
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36-49
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Affected (adult onset)
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50-1000
|
|
Affected (congenital)
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1000-2000 (in fetuses)
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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.
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.