Muscular Dystrophy

Muscular dystrophy (MD) refers to a group of genetic disorders characterized by progressive muscle weakness and degeneration. These conditions affect the skeletal muscles, which are responsible for movement, and in some forms of muscular dystrophy, they can also affect the heart and other organs.

Types of Muscular Dystrophy

There are several types of muscular dystrophy, each with different patterns of inheritance, onset, and severity:

  1. Duchenne Muscular Dystrophy (DMD):
    • The most common and severe form.
    • Primarily affects boys, with symptoms usually beginning between ages 2 and 5.
    • Caused by mutations in the dystrophin gene, leading to a lack of dystrophin protein, which is essential for muscle health.
    • Progressive muscle weakness starts in the legs and pelvis, leading to difficulty walking, running, and climbing stairs. By adolescence, most children with DMD require a wheelchair.
    • It can affect the heart (cardiomyopathy) and respiratory muscles, leading to serious complications in later stages.
  2. Becker Muscular Dystrophy (BMD):
    • Similar to Duchenne but less severe and progresses more slowly.
    • Symptoms typically begin in the teens or early adulthood.
    • Caused by a partially functional dystrophin protein, resulting in milder muscle weakness than DMD.
  3. Myotonic Dystrophy:
    • The most common form of muscular dystrophy in adults, with symptoms appearing in adolescence or adulthood.
    • Characterized by muscle stiffness (myotonia), progressive muscle wasting, and weakness, affecting the face, neck, and limbs.
    • It can also involve the heart, endocrine system, and respiratory muscles.
    • Type 1 and Type 2 are the two major forms, with Type 1 being more severe.
  4. Limb-Girdle Muscular Dystrophy (LGMD):
    • Affects both males and females and involves progressive weakness of the shoulder and hip muscles.
    • Symptoms can begin in childhood or adulthood and vary in severity.
    • Many genetic mutations can cause LGMD, affecting different proteins that maintain muscle structure.
  5. Facioscapulohumeral Muscular Dystrophy (FSHD):
    • Affects the muscles of the face, shoulders, and upper arms.
    • Symptoms typically appear in teenage years or early adulthood.
    • Muscle weakness is often asymmetric and can lead to difficulties with facial expressions, lifting objects, and raising the arms.
  6. Congenital Muscular Dystrophy (CMD):
    • Present at birth or early infancy, with muscle weakness and poor motor control.
    • Can affect both the skeletal muscles and the brain, leading to developmental delays and intellectual disabilities in some cases.
    • Severity and progression vary widely, depending on the specific genetic mutation.
  7. Emery-Dreifuss Muscular Dystrophy (EDMD):
    • Characterized by muscle weakness and wasting, primarily in the shoulders, upper arms, and calves.
    • Early-onset contractures (stiffness) in the elbows, ankles, and neck are common.
    • Affects the heart, often leading to cardiac complications like arrhythmias and conduction problems.

Causes

Muscular dystrophy is caused by mutations in the genes responsible for the structure and function of muscles. These genetic mutations can be inherited in different patterns:

  • X-linked inheritance (e.g., Duchenne and Becker muscular dystrophy): The mutated gene is located on the X chromosome, so it primarily affects males, while females are carriers.
  • Autosomal recessive inheritance (e.g., some forms of limb-girdle muscular dystrophy): Both parents must carry a copy of the mutated gene for their child to be affected.
  • Autosomal dominant inheritance (e.g., myotonic dystrophy): Only one copy of the mutated gene from either parent is enough to cause the condition.

Symptoms

The symptoms of muscular dystrophy vary based on the type and the muscles affected. Common signs and symptoms include:

  • Progressive muscle weakness: Starts in specific muscle groups, such as the legs, hips, or shoulders, and gradually spreads.
  • Muscle wasting: Over time, muscles shrink and lose mass due to lack of use and damage.
  • Difficulty with motor skills: Such as walking, running, or rising from a seated position.
  • Frequent falls and clumsiness.
  • Contractures: Stiffening of muscles and joints that limit movement.
  • Respiratory problems: As muscles that control breathing weaken.
  • Cardiac problems: Some forms affect the heart muscle, leading to arrhythmias, heart failure, or cardiomyopathy.

Diagnosis

Diagnosis of muscular dystrophy involves:

  • Genetic testing: To identify mutations in specific genes.
  • Blood tests: High levels of creatine kinase (CK), an enzyme that leaks out of damaged muscles, can indicate muscle degeneration.
  • Electromyography (EMG): Measures electrical activity in muscles to detect abnormalities.
  • Muscle biopsy: A small sample of muscle tissue is examined to assess the type and extent of muscle damage.
  • Imaging tests: MRI or ultrasound may be used to visualize muscle structure and degeneration.

Prognosis

The prognosis for muscular dystrophy depends on the type and severity of the disease:

  • Duchenne muscular dystrophy: Typically leads to loss of mobility by the teenage years, with life expectancy often reduced due to respiratory or heart complications, though advances in care have improved survival.
  • Becker muscular dystrophy: Progresses more slowly, with some individuals living into middle or late adulthood.
  • Other forms: The progression and impact of the disease vary widely, with some leading to severe disability, while others are milder and compatible with a near-normal lifespan.

Supportive care, including physical therapy, assistive devices, and medical interventions, can greatly improve the quality of life for individuals with muscular dystrophy. Ongoing research into gene therapy, stem cell therapy, and new medications offers hope for more effective treatments in the future.