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Myotonic Dystrophy Mutation Type 1

DMPK

Test Codes

BAYLOR: 6041, Testing requires pathology approval prior to collection.

Department

Send Outs

Instructions

This test is not included in the Beaumont Laboratory testing formulary, however, the Laboratory can facilitate specimen collection.

• This test requires pathology review. Contact the Send Outs Laboratory at 248-551-9045 before ordering this test.
• Testing requires the ordering physician to complete forms for the independent clinical laboratory performing the testing.
• This test will be billed to the patient's insurance. If not covered by insurance, the patient is responsible for the full cost of testing.
• Specimens received without the appropriate forms and information will not be shipped.
• Once approved, order test as a Miscellaneous Send Out (XMISC). 

Specimen Collection Criteria

Collect (Adults): Two Lavender-top EDTA tubes, after obtaining necessary pathology approval.
Also acceptable (Children/Infants): One Lavender-top EDTA tube, after obtaining necessary pathology approval.

Physician Office/Draw Specimen Preparation

Do not centrifuge. Maintain whole blood specimens at room temperature (20-26°C or 68-78.8°F).

Preparation for Courier Transport

Transport: Whole blood in EDTA tubes, at room temperature (20-26°C or 68-78.8°F) (Minimum: 3.0 mL Adult) (Minimum: 2.0 mL Child).

Rejection Criteria

Specimens received without prior laboratory notification and review.

Specimens not collected and processed as indicated. 

In-Lab Processing

Do not centrifuge. Maintain whole blood specimens at room temperature (20-26°C or 68-78.8°F).

Transport: Whole blood in EDTA tubes, at room temperature (20-26°C or 68-78.8°F). 

Storage

Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 7 days
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Specimen Storage in Department Prior to Disposal:

Specimen retention time is determined by the policy of the reference laboratory. Contact the Send Outs Laboratory with any questions.

Laboratory

Sent to Baylor Genetics, DNA Diagnostic Laboratory, Houston, TX.

Performed

Results available within 21 days.

Reference Range

By report.

Test Methodology

Polymerase Chain Reacation (PCR) Amplification, Southern Blot with Densitometry.

Interpretation

The mutation causing myotonic dystrophy has been identified as an unstable expanded (CTG)n repeat in the 3' untranslated region of the myotonin protein kinase gene on chromosome 19. Usually, normal individuals have between five and 35 repeats, mildly affected patients have 50-150 repeats, and adult onset (classical) patients have 100-1000 repeats. Transmission of mutant alleles to successive generations is generally accompanied by increases in the number of CTG repeats plus earlier onset of myotonic dystrophy and an increase in the clinical severity. Congenital cases of myotonic dystrophy usually have >1000 copies of the repeat and in all but rare cases involve maternal transmission of the mutant allele.

Clinical Utility

This assay aids in the diagnosis of myotonia (progressive muscle weakness and wasting) and for individuals suspected of having Myotonic Dystrophy.

CPT Codes

81234

Contacts

Last Updated

10/3/2023