What are Duchenne/Becker Muscular Dystrophy?
Dystrophinopathies are a group of conditions that generally cause muscle weakness. They are inherited in an X-linked manner, which means that females are far less likely to experience symptoms compared to males. However, up to 20% of females may also experience mild symptoms. Common presentations of dystrophinopathies are described below.
Duchenne Muscular Dystrophy
Duchenne muscular dystrophy (DMD) is characterized by progressive muscle weakness and degeneration. Symptoms typically begin in early childhood with the first muscles affected being those of the hips, pelvic region, thighs, and shoulders. Muscle weakness of these areas results in general motor (sitting up, standing, walking) delays and an abnormal gait (way of walking). A small percentage of males also develop learning difficulties early in life, though the level of intellectual disability is variable. Because DMD is progressive, most individuals will need a wheelchair by 13 years of age. By the mid-teenage years the heart muscles will weaken (dilated cardiomyopathy), as will the respiratory muscles, which can lead to early death.
Becker Muscular Dystrophy
Becker muscular dystrophy (BMD) is similarly characterized by muscle weakness and dilated cardiomyopathy. However, symptoms are much more variable in presentation, may be milder, and tend to develop later than DMD. In addition, a longer life expectancy is generally seen with BMD in comparison to DMD.
DMD-associated dilated cardiomyopathy
DMD-associated dilated cardiomyopathy (DMD-associated DCM) may occur without any muscle disease, and both males and females are at risk to develop this condition. However, onset is generally earlier in males than in females, and progression of DCM tends to be more rapid in males than females.
How common is Dystrophinopathy (Including Duchenne/Becker Muscular Dystrophy?
Duchenne and Becker muscular dystrophies are seen in all ethnic groups and, at most, affect about 1 in 3500 males. However, approximately 1/3 of individuals affected by DMD/BMD do not inherit a mutation from a carrier mother (de novo mutation). Of note, because the condition is X-linked, estimates generally do not include females though they are affected at a much lower rate. In the mainland China, an estimated 1 in 500 people are carriers of a genetic mutation that causes Duchenne/Becker Muscular Dystrophy.
How is Dystrophinopathy (Including Duchenne/Becker Muscular Dystrophy) treated?
There is no cure for Duchenne muscular dystrophy and the related disorders. A combination of physical therapy, medication, and regular cardiac and respiratory screenings is the current standard practice for treating the disease.
Females who are carriers for the disease are at an increased risk for dilated cardiomyopathy, and should also be seen regularly by a cardiologist.
What is the prognosis for people with Dystrophinopathy (Including Duchenne/Becker Muscular Dystrophy)?
The prognosis for Duchenne muscular dystrophy is variable, but most males will be wheelchair-dependent by age 13 and die before 30 years of age due to heart or respiratory failure. Males who have Becker muscular dystrophy have a longer life expectancy reaching into their 40s or 50s. Prognosis in females is generally better, but lifespan may still be shortened in the presence of DCM.