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Gene Analysis for Duchenne Muscular Dystrophy (DMD)
Genetic
Report in 192Hrs
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Genetic testing for DMD or NF2 mutations.
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Gene Analysis - Duchenne Muscular Dystrophy (DMD)
- Why is it done?
- Detects mutations in the DMD gene (dystrophin gene) located on the X chromosome that cause Duchenne muscular dystrophy
- Confirms diagnosis in individuals with clinical symptoms of DMD (progressive muscle weakness and degeneration)
- Identifies carriers in females who may have one mutated copy of the DMD gene
- Provides genetic counseling information for families with history of DMD
- Enables prenatal and newborn screening for affected individuals
- Performed when elevated creatine kinase (CK) levels and clinical muscle weakness are observed
- Helps determine prognosis and plan appropriate treatment and management strategies
- Normal Range
- Normal Result (Negative): No mutation detected in the DMD gene; indicates absence of Duchenne muscular dystrophy mutation
- Abnormal Result (Positive): Mutation detected in the DMD gene; specific mutation type documented
- Mutation Types: Deletions (60%), duplications (10%), or point mutations (30%)
- Genotype Status: Hemizygous in males (affected), heterozygous in females (carrier or manifesting carrier)
- Uncertain/Variant of Uncertain Significance: Sequence change found whose clinical significance is unknown; may require further investigation
- Interpretation
- Positive Result in Males (Hemizygous): Confirms Duchenne muscular dystrophy diagnosis; affected individual will develop progressive muscle weakness beginning in early childhood (usually by age 5-6), with loss of ambulation by early teens
- Positive Result in Females (Heterozygous): Indicates carrier status; females typically asymptomatic but may show manifesting carrier phenotype with variable symptoms due to X-inactivation patterns
- Deletion Mutations: Most common type; severity depends on whether deletion maintains reading frame; in-frame deletions result in milder Becker muscular dystrophy; out-of-frame deletions cause severe DMD
- Duplication Mutations: In-frame duplications typically produce milder phenotypes; out-of-frame duplications cause more severe disease
- Point Mutations: Nonsense mutations cause premature termination and severe DMD; missense mutations have variable effects on disease severity
- Negative Result: Rules out DMD; if clinical suspicion remains high despite negative DNA testing, may require muscle biopsy with dystrophin immunostaining or western blotting for confirmation
- De Novo Mutations: Approximately 33% of cases result from new mutations not inherited from parents; risk of recurrence low but carrier testing recommended for mother
- Associated Organs
- Primary Organ System - Skeletal Muscle: Progressive degeneration and weakness of voluntary muscles; proximal muscles affected first (hip and shoulder girdle)
- Cardiac Muscle: Dilated cardiomyopathy develops in majority of DMD patients; can lead to arrhythmias, heart failure, and sudden cardiac death
- Respiratory Muscle: Progressive respiratory muscle weakness leads to ventilatory insufficiency; increased risk of pneumonia and sleep-disordered breathing
- Brain: Dystrophin expressed in brain; cognitive impairment and learning disabilities common in DMD patients
- Gastrointestinal Tract: Dysphagia, gastroesophageal reflux, and constipation; dystrophin expression in smooth muscle contributes to GI motility dysfunction
- Associated Diseases: Duchenne muscular dystrophy (severe), Becker muscular dystrophy (milder variant), X-linked dilated cardiomyopathy
- Potential Complications: Loss of ambulation by age 12-15, scoliosis, contractures, cardiac arrhythmias, respiratory failure requiring mechanical ventilation, infections, premature death usually by late teens or early 20s
- Follow-up Tests
- Muscle Biopsy with Dystrophin Immunostaining: Confirms dystrophin deficiency; performed if genetic testing is negative but clinical suspicion remains high
- Creatine Kinase (CK) Level: Markedly elevated (>10,000 IU/L) in DMD; serial monitoring may be useful to track disease progression
- Electrocardiography (ECG): Recommended at diagnosis and periodically; detects cardiac involvement and arrhythmias
- Echocardiography: Baseline screening and annual monitoring to assess left ventricular function and detect cardiomyopathy
- Pulmonary Function Tests (PFTs): Baseline and periodic assessment to monitor respiratory muscle strength; typically performed annually or as needed
- Magnetic Resonance Imaging (MRI): Skeletal muscle MRI to assess fat infiltration and disease progression; cardiac MRI for comprehensive cardiac evaluation
- Genetic Counseling and Family Testing: Recommended for all affected families; carrier testing for female relatives; prenatal testing for future pregnancies
- Neuropsychological Assessment: Evaluate for cognitive impairment and learning disabilities; helpful for educational planning
- Electromyography (EMG): May be performed to confirm myopathic pattern of muscle involvement if diagnosis unclear
- Fasting Required?
- Fasting Required: No
- Sample Collection: Blood sample (5-10 mL) collected in EDTA tube via venipuncture; no special preparation needed
- Timing: Can be done at any time of day
- Medication Considerations: No medications need to be avoided; continue all current medications
- Additional Instructions: Patient should be well-rested; avoid strenuous exercise 24-48 hours before collection if possible as this may elevate CK levels; inform phlebotomist of any recent trauma or muscle injury
- Sample Storage: Blood sample should be refrigerated if not immediately processed; genetic testing may take 2-8 weeks depending on test method used (microarray, next-generation sequencing, or targeted mutation analysis)
How our test process works!
