What Is Muscular Dystrophy?

The nine different types of muscular dystrophy include:

1. Duchenne muscular dystrophy (DMD): The onset of this type is between the ages of two and five years. It occurs due to a mutation in the gene for a muscle protein called dystrophin. DMD is the most common form of muscular dystrophy.
2. Becker muscular dystrophy (BMD): It is the second most common form of muscular dystrophy and affects the hip, thigh and shoulder muscles. Symptoms and causes are similar to those of DMD. BMD symptoms begin later in life and generally are less severe compared with DMD symptoms.
3. Myotonic dystrophy: It is a rare type of inherited muscular dystrophy in which the person faces difficulty relaxing their muscles. Myotonic dystrophy typically begins between 10 and 30 years but can affect people of all ages. There are two types of myotonic dystrophy that include
   • Myotonic dystrophy I: It affects the muscles and other body systems including the heart, eyes, endocrine system and central nervous system. Myotonic dystrophy I is caused by mutation in the DMPK gene. There are two variations of myotonic dystrophy I, which include
     • Mild
     • Congenital
   • Myotonic dystrophy II: It is a milder type of myotonic dystrophy that affects the muscles and other body systems such as the heart, eyes and pancreas. Myotonic dystrophy II is caused by mutation in the CNBP gene.
4. Limb-Girdle muscular dystrophy: This type of muscular dystrophy affects the muscle of the shoulders and hips. It affects people of all ages and approximately affects 2 out of 100,000 people in the United States.
5. Facioscapulohumeral muscular dystrophy: It is the third most common form of muscular dystrophy. The disease affects the muscles in the face, shoulder blades and upper arms. The onset of this type is before 20 years of age.
6. Congenital muscular dystrophy: This may be present at birth resulting in weak muscles, curved spine and stiff or loose joints in infants. Children may face learning disabilities, seizures and vision problems.
7. Distal muscular dystrophy: This type of muscular dystrophy typically begins in adulthood. It affects the feet, hands, lower legs and lower arms. It can also affect the heart.
8. Oculopharyngeal muscular dystrophy: It is the rare form of muscular dystrophy that affects the muscles in the eyelid and throat. Symptoms such as droopy eyelids (ptosis) and difficulty swallowing usually appear in people in their 40s and 60s.
9. Emery-Dreiffuss muscular dystrophy: It mostly affects children. Children may experience weak shoulders, upper arms and calf muscles by the age of 10 years.

Most of the cases of muscular dystrophy occur due to genetic mutations. One or both parents may pass faulty genes to their child. Idiopathic muscular dystrophy or dystrophy with an unknown cause is rare.

Muscle weakness remains the prime symptom of muscular dystrophy. Depending on the type, the onset of disease varies. Other common signs of muscular dystrophy include:

1. Delayed milestones for age
2. Scoliosis (sideways curved spine)
3. Enlarged calf muscle
4. Difficulty in walking or running
5. Dysphagia (difficulty swallowing)
6. Muscle pain
7. Learning disabilities
8. Stiff or loose joints
9. Breathing problems
10. Waddling (abnormal  gait)
11. Cardiomyopathy (disease of the heart muscle)
12. Arrhythmia
13. Heart failure

Muscular dystrophy occurs due to gene mutations that affect muscle protein. As a result, the person may have muscle weakness and progressive disability.

Muscular dystrophy often runs in families, but in some cases, they occur spontaneously without any family history. A child may inherit the mutated genes from one or both parents. Parents with mutated genes and without muscular dystrophy may pass the genes to the child, thus increasing the risk of the disease. Some children may have mutated genes, but they might not develop muscular dystrophy later in life.

People may develop muscular dystrophy in one of the four ways which include

1. Autosomal dominant inherited disorder: The child inherits mutated genes from one parent with the disease.
2. Autosomal recessive inherited disorder: The child inherits the genes from both the parents. Both the genes should match and must include a mutation to cause the disease.
3. Sex-linked (X-linked) disorder: Genetic changes are passed from parents to children through the X chromosome. In this condition, the mutation is commonly seen in the X chromosome. Because women have two X chromosomes, they may have milder muscular dystrophy or may not exhibit any symptoms. On the contrary, because men have XY-type chromosomes, a mutation in the X genes can exhibit symptoms of severe forms of muscular dystrophy.
4. Spontaneous mutations: A person may develop muscular dystrophy due to spontaneous changes without a family history of the same.

Until recent years, it was common for boys with muscular dystrophy to live up until their teen years or shortly thereafter. However, with recent advancements in cardiac and respiratory care, life expectancy for people with muscular dystrophy is increasing. Currently, it is more common to see people with muscular dystrophy go on to live into their 30s. The life expectancy of different types of muscular dystrophy is summarized below: