Duchenne Muscular Dystrophy

X-linked recessive disorder caused by mutations of the dystrophin gene, resulting in severe absence (<5%) of dystrophin, a muscle cell membrane protein.

Clinical features

• Typically manifests between 2 and 3 years of age.
• Muscle weakness (Gower sign): affects proximal muscles, initially the lower limbs. Frequent toe-walking, waddling gait, lordosis. Difficulty running, jumping, climbing stairs, rising from the floor. Frequent falls, often causing limb fractures. Weakness progresses steadily; limb flexion contractures and scoliosis develop in nearly all children. Most need a wheelchair by age 12 and historically died of respiratory complications by age 20 (survival has improved with modern respiratory/cardiac care).
• Cardiac involvement: dilated cardiomyopathy, conduction abnormalities, arrhythmias — present in ~1/3 of patients by age 14, and in all patients over 18.
• ~1/3 have mild, non-progressive intellectual impairment affecting verbal ability more than performance.

Diagnosis

• Genetic testing (DNA mutation analysis) is the confirmatory test.
• Family history, electromyography, muscle biopsy.
• Baseline cardiac assessment with ECG and echocardiography.

Management

• Supportive care: exercise, non-invasive ventilatory support.
• Corticosteroids: prednisone or deflazacort.
• Antisense oligonucleotide (exon-skipping) therapies for specific mutation subtypes — options now include eteplirsen, viltolarsen and casimersen, alongside gene therapy (delandistrogene moxeparvovec) for eligible patients, under specialist care.
• Cardiomyopathy: ACE inhibitor and/or beta-blocker.
• Corrective surgery for scoliosis where needed.
• Genetic counselling.