FeedbackMultiplex Ligation-dependent Probe Amplification/Massively Parallel Sequencing
- Most comprehensive DMD gene test for DMD or BMD
- Deletion/duplication analysis is performed first
- If no large deletions or duplications are detected and/or results do not explain the clinical scenario, sequencing of the DMD gene is performed
- Deletion/duplication and sequencing components are also orderable separately, see below
Multiplex Ligation-dependent Probe Amplification
- Appropriate first-tier genetic test for diagnostic testing or carrier screening for DMD or BMD; does not detect sequence variants
- Recommended test for a known familial DMD large deletion or duplication previously identified in a family member
- A copy of the family member’s test result documenting the known familial variant is required
Massively Parallel Sequencing
- Appropriate second-tier test for diagnostic or carrier screening for DMD or BMD after result of deletion/duplication analysis is negative
Massively Parallel Sequencing
- Testing for a known familial sequence variant by sequencing gene of interest. A copy of the family member’s test result documenting the familial gene variant is REQUIRED.
- For prenatal testing, see Familial Targeted Sequencing, Fetal (3005869).
- To determine if the variant(s) of interest are detectable by this assay, contact an ARUP genetic counselor at 800-242-2787.
Multiplex Ligation-dependent Probe Amplification
- This test is performed on prenatal samples at risk for a known familial DMD deletion or duplication.
- A copy of the family member's test result documenting the known familial variant is required.
See Related Tests
Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are X-linked degenerative muscle disorders caused by pathogenic variants in the DMD gene. Testing for DMD variants can be used to confirm a diagnosis of DMD/BMD in symptomatic individuals or to determine carrier status for females with a family history of DMD/BMD or dilated cardiomyopathy (DCM). Prenatal testing for familial DMD variants is also available.
Disease Overview
Symptoms
- DMD
- Delayed childhood milestones (eg, sitting, standing, walking, climbing) due to progressive symmetrical muscular weakness
- Cardiomyopathy onset – ~14 years
- 95% have cardiovascular involvement
- Wheelchair dependence – typically by 12 years
- Laboratory findings
- No observable dystrophin expression
- Serum CK levels – significantly increased
- BMD
- Later-onset muscle weakness
- Cardiomyopathy onset – ~15 years
- Wheelchair dependence – 20s-30s
- Laboratory findings
- Dystrophin expression – 20-100%
- Serum CK levels – increased
- DMD-Associated Dilated Cardiomyopathy (DCM)
- Rapidly progressive disease course in the absence of skeletal myopathy
- Male age of onset – teens and 20s
- Female age of onset – 30s and 40s
Incidence
- DMD – 1/3,500 male births worldwide
- BMD – 1/19,000 male births worldwide
Genetics
Gene – DMD
Inheritance – X-linked
Penetrance
- Males – 100%
- Females – varies with X-chromosome inactivation
De novo variants – ~1/3 cases
Typical Diagnostic Testing Strategy
- Initial testing for DMD/BMD
- Serum creatine kinase (CK) concentration
- Muscle biopsy with dystrophin studies
- Molecular testing
- Deletion/duplication analysis
- Sequencing analysis
Typical Carrier Testing Strategy
- For a known familial DMD variant, targeted testing is recommended.
- If there is a family history of DMD/BMD but the causative familial variant is unknown, test an affected relative then perform targeted testing for the identified variant in at-risk relatives.
- If an affected relative cannot be tested, at-risk relatives should be tested by deletion/duplication analysis first because most DMD variants are large deletions and duplications.
- If negative, consider DMD sequencing.
Recommended Follow-Up Testing
Cardiac evaluation for affected individuals and carriers
Test Description
Clinical Sensitivity
- DMD
- Deletion/duplication – 55-75%
- Sequencing – 20-35%
- BMD
- Deletion/duplication – 75-90%
- Sequencing – 10-20%
Results
- Positive
- One pathogenic variant detected in DMD gene
- Causative for DMD/BMD in males
- Female carriers are variably affected
- One pathogenic variant detected in DMD gene
- Negative
- No pathogenic variants identified
- Risk for being affected with, or a carrier of, DMD/BMD, is reduced but not excluded.
- No pathogenic variants identified
- Inconclusive
- Variants of uncertain clinical significance detected
- Whether variants are benign or pathogenic is unknown
Limitations
- A negative result does not exclude a heritable form of muscular dystrophy.
- Diagnostic errors can occur due to rare sequence variations.
- Interpretation of this test result may be impacted if the individual has had an allogeneic stem cell transplantation.
- The following will not be evaluated:
- Variants outside the coding regions and intron-exon boundaries of the targeted gene(s)
- Regulatory region variants and deep intronic variants
- Breakpoints of large deletions/duplications
- Noncoding transcripts
- The following may not be detected:
- Deletions/duplications/insertions of any size by massively parallel sequencing
- Some variants due to technical limitations in the presence of pseudogenes, repetitive, or homologous regions
- Low-level somatic variants
Analytical Sensitivity
- For MLPA – greater than 99%
- For massively parallel sequencing:
-
Variant Class Analytical Sensitivity (PPA) Estimatea (%)
Analytical Sensitivity (PPA) 95% Credibility Regiona (%)
SNVs
99.2
96.9-99.4
Deletions 1-10 bp
93.8
84.3-98.2
Deletions 11-44 bp
100
87.8-100
Insertions 1-10 bp
94.8
86.8-98.5
Insertions 11-23 bp
100
62.1-100
DMD gene is a subset of a larger methods-based validation from which the PPA values are derived.
bp, base pairs; PPA, positive percent agreement; SNVs, single nucleotide variants
GeneReviews - Dystrophinopathies
Darras BT, Urion DK, Ghosh PS. Dystrophinopathies. In: Adam MP, Ardinger HH, Pagon RA, et al, editors. GeneReviews, University of Washington; 1993-2020. [Last update: Apr 2018; Accessed: Feb 2020]