Myotonic Dystrophy
Myotonic dystrophy is the most common form of adult onset
muscular dystrophy and has an incidence of 1/8000 individuals.
The genetic defect in the disorder is the expansion of a (CTG)
trinucleotide repeat in the DM gene. This autosomal dominant
disorder is characterized by myotonia, muscle wasting, frontal
balding, hypogonadism, and ocular and ECG abnormalities. Genetic
anticipation is commonly seen in families with myotonic dystrophy.
In these families, extreme amplification can occur during mother
to child transmission of the abnormal allele leading to a congenital
form of the disease. Congenital myotonic dystrophy can be associated
with a very severe disease state including generalized hypotonia
and mental retardation. Molecular diagnosis of myotonic dystrophy
at the Greenwood Genetic Center involves a combination of Southern
blotting tests and direct PCR analysis to determine the (CTG)
repeat number. Prenatal testing is available via material from
CVS or amniocentesis.
Specimen requirements: 5 to 10 ml of peripheral blood
collected in an EDTA (lavender top) Vacutainer tube is preferred.
The minimal blood needed for reliable DNA isolation is 3 ml.
If necessary, ACD solution A Vacutainer tubes (yellow top)
may be substituted. Prenatal studies require two confluent T-25
flasks containing cultured CVS material or amniocytes. A maternal
blood sample is also requested for prenatal analysis.
Transport: Please contact the Molecular Diagnostic Laboratory Coordinator
(1-800-473-9411) for shipping
information. The specimen should be kept at room temperature
and delivered via overnight shipping. FedEx delivery is preferred.
If shipment is delayed by one or two days, the specimen should
be refrigerated and shipped at room temperature. Do not freeze
the specimen. Samples collected on a Friday can be safely
designated for Monday delivery.
Analysis standards: Analysis will be completed within
2-3 weeks from sample receipt. The quality and interpretation of
test results are assessed by the laboratory director. Technical
staff independently assess the quality and interpretation of
the test. The Greenwood Genetic Center Molecular Diagnostic Laboratory
is CLIA certified and actively participates in CAP proficiency
surveys.
Reporting of Test Results: Test results and their interpretation
will be mailed and/or faxed following completion of the test.
Verbal reports will be telephoned to the person(s) requesting
the test when an abnormal test result occurs. Consultation with
the laboratory director is available and explanations of testing
protocols will be supplied upon request.
CPT Codes: 83890, 83892, 83896,
83898, 83909, 83912
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