Duchenne/Becker Muscular Dystrophy: DMD Deletion/Duplication MLPA

Clinical Information

Both Duchenne muscular dystrophy and the milder Becker muscular dystrophy are due to variants in the dystrophin gene located on the X chromosome. The characteristic features of these disorders include pseudohypertrophy of the calf muscle, myofiber degeneration, myopathic EMG changes, and dramatic elevations of serum creatine kinase. Approximately two-thirds of variants in the dystrophin gene are due to deletions and duplications. The majority of the remaining dystrophin defects result from point variants within the gene.

Technical Information

• This test is performed using Multiplex Ligation-dependent Probe Amplification (MLPA).
• MLPA analysis is performed to determine if large deletions or duplications involving one or more exons of the dystrophin gene (DMD) are present. MLPA is a molecular technique that allows for the determination of dosage for specific sequences of interest (Schouten et al. (2002) Nucleic Acids Research 30:e57).
• Probes for all 79 dystrophin exons of the full-length muscular isoform (transcript variant DP427m) as well as one probe for exon 1 of the brain-specific alternative isoform (transcript variant DP427c), in combination with a variety of control probes, are analyzed and quantified.

Specimen Requirements

• The preferred sample type is 3-4 ml of peripheral blood collected in an EDTA (purple top) tube. Extracted DNA and saliva are also accepted for this test. Blood and saliva kits are available by request.
• Send approximately 5µg of extracted DNA at a requested concentration of 90-130 ng/µl.
• Saliva samples must be submitted in an approved saliva kit.

Transport Instructions

• The blood 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.
• Extracted DNA should be sent at room temperature via overnight delivery.
• Saliva is stable at room temperature and can be delivered via overnight or ground shipping.

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.

Prenatal Specimen Requirements

• Amniotic Fluid: Direct amniotic fluid will be accepted for analysis given there is sufficient volume for back-up culture to be established. A back-up culture at a reference lab OR Greenwood lab is required. Additional charges may apply if cell culture is required after receipt of the sample. If sending direct fluid for molecular analysis only, 10-20 ml of amniotic fluid is requested. Chromosome studies will require an additional 10-15 ml of fluid.
• Chorionic Villi Sample (CVS): 10-50 mg of chorionic villi is requested in a sterile tube with CVS media. Direct testing on CVS is not available; an additional 1-3 weeks may be needed for cultures to grow.
• Cultured amniocytes/CVS: 2x T25 confluent flasks
• A maternal sample is required, and accepted sample types include blood, saliva, and extracted DNA. Please refer to the specimen requirements above for more information.

Prenatal Transport Instructions

• Amniotic fluid should be kept at room temperature; do not freeze or refrigerate. Specimen should be sent by courier or overnight mail to arrive at the laboratory the next day. FedEx is preferred.
• CVS and cultured amniocytes should be kept at room temperature; do not freeze or refrigerate. Specimen should be sent by courier or overnight mail to arrive at the laboratory the next day. FedEx is preferred.
• Please refer to the transport instructions above for sending the maternal sample.