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
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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
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Affected (congenital)
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1000-2000 (in fetuses)
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Specimen Requirements:
Blood: EDTA or ACD (Solution A or B):
- Adult: 5mL
- Child: 5mL
- Infant: 2-3mL
Saliva: 2 ORAgene Saliva Kits (OGR-500) used according to manufacturer instructions. Please contact KDL Client Services for a Saliva Collection Kit for patients that cannot provide a blood sample.
Assisted Saliva: 4 ORAgene Assisted Saliva Kits (OGR-575) used according to manufacturer instructions. Please contact KDL Client Services for an Assisted Saliva Collection Kit for patients that cannot provide a blood sample.
Buccal Cells: 4 CytoSoft™ Cytology Brush (Medical Packaging CYB-1) used according to manufacturer instructions. Please contact KDL Client Services for a Buccal Collection Kit for patients that cannot provide a blood sample.
Skin Fibroblast: Punch Biopsy (cell cultures will be prepared at KDL and used for testing), or 2 T-25 confluent flasks
Prenatal:
Direct Amniotic Fluid (10-20mL)Direct CVSDirect POCCultured Amniocytes (2-T25 flasks)Cultured CVS (2-T25 flasks)Cultured Fetal Tissue: Product of Conception (2 T-25 flasks)Cord Blood (1-2mL)
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).
Notice Regarding Molecular Genetic Testing on Prenatal Specimens:
Maternal cell rule-out testing will be performed on all prenatal specimens received. Please provide maternal blood (or saliva) in addition to the fetal specimen. Additional charges apply for the maternal cell rule-out test.
For routine testing of blood and saliva (or DNA extracted from these specimens), KDL does NOT accept samples from patients within two (2) weeks of a packed cell/platelet transfusion or within four (4) weeks of a whole blood transfusion. For extraordinary circumstances, where testing must be performed within the above windows, please contact the laboratory.
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.