Becker Muscular Dystrophy

Becker muscular dystrophy (BMD) is the milder X linked dystrophinopathy from in frame DMD mutations producing partially functional dystrophin.

• Incidence 1 in 18,000 to 30,000 male births.

• Onset 5 to 15 years, often later; ambulation retained beyond 16 years, often into adulthood.

• Cardiomyopathy is prominent and may precede skeletal weakness; major cause of death.

• Spectrum includes isolated cardiomyopathy and exercise intolerance with cramps.

• Proximal weakness (hips, thighs first), calf pseudohypertrophy, exercise cramps and myoglobinuria.

• Dilated cardiomyopathy, heart failure, arrhythmia in 60 to 70% by age 40.

• Variable cognitive involvement. Female carriers may have cardiomyopathy.

• CK 5 to 50 times normal.

• DMD gene analysis (in frame deletions, duplications, point mutations); muscle biopsy: reduced or abnormal dystrophin by Western blot.

• Cardiac MRI (late gadolinium enhancement), echocardiogram, Holter, from diagnosis.

• Exclude limb girdle dystrophies and metabolic myopathies.

• Cardiac surveillance every 1 to 2 years from diagnosis, then treat early: ACE inhibitor or ARB, beta blocker (bisoprolol, carvedilol), eplerenone 25 to 50 mg, sacubitril/valsartan; ICD for ventricular arrhythmia; LVAD or transplant for end stage.

• Corticosteroids are used selectively (limited evidence).

• Exercise: avoid eccentric and strenuous activity; supervised submaximal aerobic exercise.

• Respiratory function monitoring, vaccination.

• Physiotherapy, orthoses, scoliosis care, bone health.

• Genetic counselling for carrier females; carrier cardiac screening.