Muscular Dystrophy

What causes muscular dystrophy

Each type is caused by changes in a gene needed for healthy muscle fibers. In Duchenne and Becker, the gene affected makes dystrophin, a protein that stabilizes muscle cell membranes during contraction. Without it, muscle fibers are damaged with use and gradually replaced by fat and scar tissue.

Inheritance patterns vary:

• X-linked: Duchenne and Becker mainly affect boys. Mothers may be carriers. About a third of Duchenne cases arise from new mutations
• autosomal dominant: myotonic dystrophy, facioscapulohumeral dystrophy, some limb-girdle types
• autosomal recessive: many limb-girdle and congenital types

Main types

Symptoms

Duchenne muscular dystrophy

• late walking (after 18 months)
• frequent falls, clumsiness, difficulty running and jumping
• waddling gait and walking on toes
• Gowers' sign: using the hands to "walk up" the legs to stand from the floor
• enlarged calf muscles (pseudohypertrophy)
• learning and speech delays in some boys (developmental delays)
• progressive muscle weakness, loss of walking, scoliosis
• heart muscle disease (cardiomyopathy) and breathing muscle weakness in teens and adults

Other types

Symptoms depend on which muscles are affected and may include weakness of the face, shoulders, hips or hands, muscle stiffness, drooping eyelids, swallowing difficulty, heart rhythm problems and fatigue.

Diagnosis

• creatine kinase (CK) blood test: very high in Duchenne and Becker, often 10 to 100 times normal
• genetic testing: confirms the type and specific mutation, which determines eligibility for targeted therapies
• muscle biopsy: sometimes, to examine protein levels
• electromyography (EMG) and nerve studies in some adult forms
• heart tests: ECG, echocardiogram and cardiac MRI
• breathing tests: lung function and sleep studies
• carrier testing for female relatives in X-linked types

Some US states and countries are adding Duchenne to newborn screening programs.

Treatment

Care is coordinated by a neuromuscular specialist team.

Medicines

• corticosteroids (prednisone, deflazacort) or vamorolone slow muscle decline in Duchenne and delay loss of walking
• exon-skipping therapies (such as eteplirsen, golodirsen, viltolarsen, casimersen) for boys with specific mutations
• gene therapy (delandistrogene moxeparvovec) for selected patients with Duchenne
• givinostat for Duchenne
• heart medicines such as ACE inhibitors and beta blockers to protect the heart
• mexiletine for myotonia in myotonic dystrophy

Supportive care

• physical therapy and stretching to delay contractures
• night splints, braces and wheelchairs
• scoliosis surgery when needed
• breathing support: cough assist devices and non-invasive ventilation (BiPAP), often at night first, to prevent respiratory failure
• bone health: vitamin D, calcium, bisphosphonates
• nutrition, swallowing support and weight management
• psychological, educational and social support

Outlook

Outlook depends on the type. With modern care, people with Duchenne now commonly live into their 30s and beyond, compared with late teens in earlier decades. Becker, myotonic and facioscapulohumeral dystrophies usually have a near-normal or modestly reduced life span, with variable disability.

Frequently asked questions

What is muscular dystrophy?

Muscular dystrophy is a group of inherited diseases in which faulty genes for muscle proteins cause muscles to weaken and waste away over time. There are more than 30 types, differing in age of onset, muscles affected and speed of progression.

What are the first signs of muscular dystrophy?

In Duchenne, early signs include late walking, frequent falls, difficulty running or climbing stairs, a waddling gait, toe walking, enlarged calves and using the hands to push up from the floor. Adult forms may start with hand, face or shoulder weakness.

Is muscular dystrophy inherited?

Yes. Duchenne and Becker are X-linked and mainly affect boys, with mothers often carriers. Other types are passed on in dominant or recessive patterns. Some cases arise from new mutations without family history.

What is the life expectancy with muscular dystrophy?

It varies by type. With modern care, many people with Duchenne live into their 30s or longer. Becker and many adult-onset types have near-normal or modestly reduced life expectancy. Heart and breathing care are key.

Can muscular dystrophy be cured?

There is no cure yet. Corticosteroids, exon-skipping drugs and gene therapy can slow Duchenne progression in eligible patients. Physical therapy, heart medicines and breathing support help all types. Research is advancing rapidly.