Causes and Risk Factors of Muscular Dystrophy

If you have muscular dystrophy or suspect you have it, you need to check in with your doctor. Properly understanding and treating this disease is paramount to successful management of the condition. And one important component of understanding the disease is knowing what causes muscular dystrophy.

There are more than 30 different types and manifestations of muscular dystrophy. Since it is a genetic disease, the type you have depends on which mutation has taken place on a specific gene. Other factors may also play a role, and each type may carry with it a different prognosis and treatment course.

The most common types of muscular dystrophy include:

• Myotonic (also known as Steinert's disease)
• Duchenne muscular dystrophy
• Becker
• Limb-girdle
• Congenital
• Oculopharyngeal
• Facioscapulohumeral
• Distal
• Emery-Dreifuss

To understand the cause of muscular dystrophy, you need to understand how the disease affects your muscles. Muscular dystrophy is characterized by progressive weakness and wasting of muscle cells.

Muscles are made up of bundles of fiber. Within each muscle fiber are clusters of myofibrils—the building blocks of muscle that allow them to contract. In addition to myofibrils, muscle fibers contain different types of proteins that work together to srtrengthen and protect the muscles from injury during the process of contraction and relaxation.

Abnormalities in these proteins caused by genetic defects lead to the muscle weakness and wasting that characterizes muscular dystrophy.

What Is Dystrophin?

Dystrophin is an important protein present in muscle fibers. The absence of dystrophin leads to the development of Duchenne muscular dystrophy. When there are faults in the production of dystrophin, Becker muscular dystrophy occurs.

Abnormalities in other proteins in muscle fibers are thought to cause the other forms of muscular dystrophy.  

There are three types of inheritance patterns in patients with muscular dystrophy.

X-linked Recessive: In this case the genetic anomaly that causes muscular dystrophy lies on the X chromosome. Therefore, only boys are affected. They would have received the faulty X chromosome from their mothers, who carry the gene but do not have the disease. Duchenne, Becker, and Emery-Dreifuss are examples of X-linked recessive muscular dystrophy.

Autosomic Recessive: In this type of inherited muscular dystrophy, the faulty gene is passed down from both parents, neither of whom will have symptoms of the disease. Their children (of either sex) will have a 25% chance of developing muscular dystrophy. An example of autosomic recessive muscular dystrophy is Limble-Girdle Dystrophy Type 2.

Autosomic Dominant: In this form of muscular dystrophy, the faulty gene comes from one parent and can affect half of their offspring regardless of sex. The affected parent often has clinical manifestations of the disease but these may be so mild as to be unnoticeable. Myotonic, facioscapulohumeral, and oculopharyngeal dystrophies are examples of autosomic dominant dystrophies.

Occasionally patients with muscular dystrophy have no family history of the disease. This may be due to the development of a first-time mutation (also called a "de novo" mutation) affecting the egg or sperm of one of the parents or a fertilized egg itself.

Since there is a genetic factor for acquiring muscular dystrophy, there is no lifestyle change that you can make to decrease your likelihood of getting it. If the genetic makeup is there and active in specific chromosomes in your body, you may get muscular dystrophy.

However, researchers have identified risk factors for complications and early death for those who already have muscular dystrophy. In a 2017 study published in the Journal of the American Heart Association, researchers identified three common risk factors that were present in people with Duchenne muscular dystrophy associated with cariomyopathy who experienced poor outcomes including early death. These included:

• Being underweight as measured by the body mass index
• Having poor lung function
• Having a high blood concentration of a protein linked to cardiac damage

Understanding the cause of muscular dystrophy can help put your mind at ease. It is a hereditary disease determined by genetics. This leaves little you can do to prevent it from occurring, but if you have muscular dystrophy, you should work closely with your doctor and medical team to maximize your overall function and outcome.