Muscular dystrophies

Muscular dystrophies are a group of inherited diseases characterized by progressive muscle degeneration and weakness. They are caused by mutations in genes encoding muscle proteins. Over 40 causative genes have been identified.

Duchenne muscular dystrophy (DMD) is the most common and most rapidly progressive muscular dystrophy. It is an X-linked condition and so usually affects only boys. Most patients lose the ability to walk by 12 years of age and require ventilatory support by 20 years of age.

Diagnosis of DMD is often delayed. Signs that indicate possible DMD include: delayed motor milestones, frequent falls, abnormal gait, muscle pain, calf hypertrophy, speech and language delay, and difficulty with jumping, running, climbing steps, and rising from the floor. Creatine kinase levels are elevated. Diagnosis is confirmed by genetic testing.

Multidisciplinary care for patients with DMD is focused on prolonging function, symptom management, and maintaining a good quality of life for as long as possible. Survival has been improved by the use of noninvasive respiratory support and cardioprotective drugs. Severe scoliosis and the need for corrective surgery can be avoided, and the need for mechanical ventilation delayed, by early and aggressive use of corticosteroids.

With few exceptions, all generalized muscle dystrophies can be managed using the principles for managing DMD. This is also the case for spinal muscular atrophy (SMA), an inherited motor neuronopathy with symptoms similar to those of the muscular dystrophies. Drugs for treating SMA are now available in clinical practice.

Muscular dystrophies are progressive, generalized diseases of muscle, most often caused by defective or specifically absent glycoproteins (e.g., dystrophin) in the muscle membrane. All muscular dystrophies are characterized by ongoing degeneration and regeneration of muscle fibers. The most common and rapidly progressive muscular dystrophy is the X-linked Duchenne muscular dystrophy (DMD), which is diagnosed by testing for DMD gene deletion or duplication. Becker muscular dystrophy is related to DMD but is less severe. Other muscular dystrophies include myotonic dystrophy, Emery-Dreifuss muscular dystrophy, facioscapulohumeral muscular dystrophy, limb-girdle muscular dystrophies, and congenital muscular dystrophies. This topic will focus mainly on DMD, with some discussion of other muscular dystrophies and of the related condition spinal muscular atrophy.