Duchenne and Becker muscular dystrophy

What it is

Duchenne and Becker muscular dystrophy are two forms of one genetic disease. Both are X-linked recessive and both come from a mutation in the dystrophin gene. What separates them is how much dystrophin is left: in Duchenne it is absent, in Becker it is reduced. They sit among the genetic myopathies, next to the limb girdle muscular dystrophies, the congenital myopathies, the mitochondrial ones and the metabolic ones from a glycogen or lipid disorder, and apart from the acquired myopathies, which are the inflammatory ones, the endocrine ones and those from drugs.

How it presents

The muscle problem is progressive paresis and atrophy that starts in the proximal lower limbs, at the pelvic girdle, and extends to the upper body and the distal limbs as the disease goes on. Reflexes are weak. The gait is waddling, and there are frequent falls from poor balance. Rising from the floor is done by the Gower maneuver, also written as Gowers sign: the child needs to turn prone to rise and uses his hands to climb up on his knees before standing. Calf pseudohypertrophy is present. Lumbar lordosis and scoliosis follow, and cognitive impairment is listed alongside. The cardiac and respiratory muscles are involved as well. Age of onset separates the two: 2 to 5 years in Duchenne, after 15 years in Becker. Duchenne is the rapid one, with inability to walk by approx. 12 years, while Becker is less severe and slower, and cardiac involvement in Becker is more common.