Myotonic dystrophy : DMPK Trinucleotide Repeat Analysis

Test Information

DMPK trinucleotide repeat analysis is a molecular test used to identify expanded CTG repeats in the gene associated with type 1 myotonic dystrophy.

Turnaround Time

3 weeks

CPT Code(s)

81234

Cost

$350

Genes

Clinical Information

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 DMPK 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 intellectual disability. Molecular diagnosis of myotonic dystrophy involves a combination of Southern blotting tests and direct PCR analysis to determine the (CTG) repeat number.

Indications

Molecular testing is useful to confirm the diagnosis and to identify the disease causing mutations within a family to allow for carrier testing and prenatal diagnosis.

Methodology

Trinucleotide Repeat

Detection

PCR and Southern blot analysis are used in combination to determine allele repeat size. PCR will detect up to approximately 100 CTG repeats while Southern blot is used to detect the larger repeats.

Specimen Requirements

5 to 7 ml of peripheral blood collected in an EDTA (lavender top) tube is the preferred specimen type. The minimal blood needed for reliable DNA isolation is 3 ml. Extracted DNA is also accepted for this test.

Transport Instructions

The specimen should be kept at room temperature and delivered via overnight shipping. 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 Friday can be safely designated for Monday delivery.

Prenatal Testing Information

Prenatal diagnosis is available if the familial mutations are known. Additional fees for cell culture and maternal cell contamination may apply. Maternal cell contamination studies are required for all prenatal molecular tests. Contact the laboratory prior to sending a prenatal specimen.

Have Questions Need Support?

Call our laboratory at 1-800-473-9411 or contact one of our Laboratory Genetic Counselors for assistance.
Robin Fletcher, MS, CGC
Kellie Walden, MS, CGC

Molecular Testing, Other Molecular Testing, Trinucleotide Repeat Analysis
One Mother's Story

One Mother's Story

After a long three-year struggle trying to have children, our son, Charlie, was born on April 18, 2009. He was our miracle...perfect in every way! When Charlie was five days old, our pediatrician called to notify us that one of the numbers from the heel prick test was a bit high. We headed to the hospital that afternoon for more tests. I will never forget the following day. It was cool and crisp - not a cloud in the sky....

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