Muscular Dystrophy Types: Facts and General Information
Disabled World: Revised/Updated: 2018/10/07
Synopsis: Muscular dystrophy refers to a group of genetic hereditary muscle diseases that cause progressive muscle weakness.
What is Muscular Dystrophy?
Muscular Dystrophy (MD) is defined as a group of muscle diseases that weaken the musculoskeletal system and hamper locomotion. Muscular dystrophies are characterized by progressive skeletal muscle weakness, defects in muscle proteins, and the death of muscle cells and tissue. There is no currently known cure for MD, although significant headway is being made with antisense oligonucleotides.
Nine diseases including Duchenne, Becker, limb girdle, congenital, facioscapulohumeral, myotonic, oculopharyngeal, distal, and Emery-Dreifuss are always classified as muscular dystrophy but there are more than 100 diseases in total with similarities to muscular dystrophy.
Most types of MD are multi-system disorders with manifestations in body systems including the heart, gastrointestinal and nervous systems, endocrine glands, skin, eyes and other organs.
The best-known type, Duchenne muscular dystrophy (DMD), is inherited in an X-linked recessive pattern, meaning that the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes, and is thus considered sex-linked. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition.
In females (who have two X chromosomes), a mutation must generally be present in both copies of the gene to cause the disorder (relatively rare exceptions, manifesting carriers, do occur due to dosage compensation/X-inactivation).
Males are therefore affected by X-linked recessive disorders much more often than females.
A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons. In about two thirds of DMD cases, an affected male inherits the mutation from a mother who carries one altered copy of the DMD gene. The other one third of cases probably result from new mutations in the gene. Females who carry one copy of a DMD mutation may have some signs and symptoms related to the condition (such as muscle weakness and cramping), but these are typically milder than the signs and symptoms seen in affected males. Duchenne muscular dystrophy and Becker's muscular dystrophy are caused by mutations of the gene for the dystrophin protein and lead to an overabundance of the enzyme creatine kinase. The dystrophin gene is the largest gene in humans.
Types of Muscular dystrophy
There are more than 30 forms of muscular dystrophy including the principal ones listed below:
Becker's Muscular Dystrophy
Also caused by a deficiency of dystrophin, and with symptoms similar to those of DMD, Becker can progress slowly or quickly.
Patients with Becker MD may:
Fall down a lot.
Walk on their tiptoes.
Have cramping in their muscles.
Have difficulty rising from the floor.
Becker MD appears primarily in males between ages 11 and 25. Some people may never need to use a wheelchair, while others lose the ability to walk during their teens, mid-30s, or later.
Congenital Muscular Dystrophy
About half of all U.S. cases with congenital MD are caused by a defect in the protein merosin, which surrounds muscle fibers. When caused by defects in other proteins, this type of MD may also affect the central nervous system.
People with congenital MD may:
Have foot deformities.
Have intellectual disabilities.
Have trouble breathing and swallowing.
Develop scoliosis (curvature of the spine).
Have problems with motor function and muscle control that appear at birth or during infancy.
Develop chronic shortening of muscles or tendons around joints, which prevents joints from moving freely.
This form of MD appears at birth or by age 2. Congenital means "present from birth." Congenital MD affects both boys and girls, who often require support to sit or stand and may never learn to walk. Some patients die in infancy, but others live into adulthood with only mild disability.
Distal Muscular Dystrophy
Distal MDs refer to a group of diseases that affect the muscles of the forearms, hands, lower legs, and feet. They are caused by defects in the protein dysferlin5 and can occur in both men and women. Distal MD may cause:
Difficulty extending fingers.
Inability to perform hand movements.
Trouble walking and climbing stairs.
Inability to hop or stand on the heels.
This form typically appears between ages 40 and 60. Distal MD is less severe and progresses more slowly than other forms of MD, but it can spread to other muscles. Patients may eventually need a ventilator.
Duchenne Muscular Dystrophy (DMD)
The most common and severe form of MD among children, DMD accounts for more than 50% of all cases. DMD is caused by a deficiency of dystrophin, a protein that helps strengthen muscle fibers and protect them from injury.
Weakness begins in the upper legs and pelvis. People with DMD may also:
Fall down a lot.
Waddle when walking.
Have difficulty running and jumping.
Have trouble rising from a lying or sitting position.
Have calf muscles that appear large because of fat accumulation.
DMD appears typically in boys between ages 3 and 5 and progresses rapidly. Most people with DMD are unable to walk by age 12 and may later need a respirator to breathe. They usually die in their late teens or early 20s from heart trouble, respiratory complications, or infection.
Emery-Dreifuss Muscular Dystrophy
Affecting boys primarily, the two forms of Emery-Dreifuss MD are caused by defects in the proteins that surround the nucleus in cells.
Have a rigid spine.
Walk on their toes.
Develop shoulder deterioration.
Have elbows locked in a flexed position.
Experience mild weakness in their facial muscles.
Weakness begins in the upper arm and lower leg muscles.
People with this form may also develop chronic shortening of muscles around joints, in the spine, ankles, knees, elbows, and back of the neck.
Symptoms usually begin by age 10 but can appear in patients up to their mid-20s. People with this form often develop heart problems by age 30, and they may die in mid-adulthood from progressive pulmonary or cardiac failure.
FSHD refers to the areas affected: the face (facio), the shoulders (scapulo), and the upper arms (humeral). Researchers don't know what gene causes FSHD. They do know where the defect occurs and that it affects specific muscle groups.
FSHD MD often appears first in the eyes (difficulty in opening and shutting) and mouth (inability to smile or pucker). Other symptoms may include:
Trouble swallowing, chewing, or speaking.
Swayback curve in the spine, called lordosis.
Impaired reflexes only at the biceps and triceps.
Muscle wasting that causes shoulders to appear slanted and shoulder blades to appear "winged".
FSHD affects teen boys and girls typically but may occur as late as age 40. Most individuals have a normal life span, but symptoms can vary from mild to severely disabling.
Limb-Girdle Muscular Dystrophy
Affecting both males and females, different types of limb-girdle are caused by different gene mutations. Patients with limb-girdle inherit a defective gene from either parent, or, in the more severe form, the same defective gene from both parents.
Patients with limb-girdle MD may:
Fall down a lot.
Have a rigid spine.
Waddle when they walk.
Have trouble rising from chairs, climbing stairs, or carrying things.
First develop weakness around the hips, which then spreads to the shoulders, legs, and neck.
This form of MD can appear in childhood but most often appears in adolescence or young adulthood. Limb-girdle can progress quickly or slowly, but most patients become severely disabled (with muscle damage and inability to walk) within 20 years of developing the disease.
Myotonic Muscular Dystrophy
The most common adult form of MD, myotonic MD appears in two forms, type 1 and type 2. Type 1 is more common and is caused by an abnormally large number of repeats of a three-letter "word" (CTG) in genetic code. While most people have up to 37 repeats of CTG, people with myotonic can have up to 4,000. The number of repeats may reflect the severity of symptoms.
Myotonic MD causes an inability to relax muscles following a sudden contraction. Other symptoms include:
Long, thin face and neck.
Irregular menstrual periods.
Baldness at the front of the scalp.
Drooping eyelids, cataracts, and other vision problems.
Heart problems that may lead to death during the 30s or 40s.
Myotonic MD affects both men and women between ages 20 and 30.
Oculopharyngeal Muscular Dystrophy
This form occurs in both men and women, and it can be mild or severe. It is caused by a defect in a protein that binds to molecules that help make other proteins. It is common among Americans of French-Canadian descent, Jewish Ashkenazi, and Hispanics from the Southwest region.
Oculopharyngeal MD may cause:
Drooping eyelids and other vision problems.
Muscle wasting and weakness in the neck, shoulders, and sometimes limbs.
This form of MD typically appears in a person's 40s or 50s. Some people will eventually lose their ability to walk.
Symptoms of Muscular Dystrophy
- Calf Pain
- Poor Balance
- Waddling Gait
- Frequent Falls
- Gonadal Atrophy
- Inability to walk
- Walking Difficulty
- Muscle Contractions
- Respiratory Difficulty
- Limited Range of Movement
- Drooping Eyelids (ptosis)
- Scoliosis (curvature of the spine)
- Progressive Muscular Wasting (weakness)
- Some types of Muscular Dystrophy can affect the heart, causing cardiomyopathy or arrhythmias.
Principal and obvious symptoms include:
- Inability to exercise or even play can cause obesity.
- Stiffening of the muscles near the joints (Joint contractures).
- In the Duchenne form, there is usually a delay in the development, in children, of the basic muscle skills and coordination.
- Vision problems due to Cataracts, baldness on the front of the head, eyelid drooping, atrophy of the gonads and even mental impairment.
- The wasting of muscle, which occurs over time and is progressive, muscle weakness and the loss of function or ability to control the muscles.
- The most Common signs are those of poor balance with the child experiencing frequent falls, difficulty with walking, waddling with a duck like gait, pain in the calves of the legs and a limited range of movement.
How is Muscular Dystrophy Diagnosed by a Doctor?
Dystrophic arm bicep muscle.
It is a known fact that Muscular Dystrophy is a genetic or inheritable disease. It is still a mystery why two individuals who are genetically the same often get Muscular Dystrophy of different severities. The diagnosis of MD is based on a combination of clinical presentation, blood tests and the results of muscle biopsy.
A physical examination or medical history is critical and your doctor will ask you all types of questions about any concerns or symptoms you have, your past health history, your family's health history, any medications that you are taking, any known allergies you have and other issues.
Certain tests can help the doctor determine exactly which type of Muscular Dystrophy you have and eliminate any other diseases that can affect the muscles or nerves. Some tests are able to measure how the nerves and muscles are actually functioning. Other tests will be to check the blood for specific levels of certain enzymes and the proteins that are involved in converting food to energy. The presence of abnormally high blood levels of specific enzymes from the muscle cells is typically present in many people with the disease.
Sometimes it is necessary to obtain a muscle biopsy. If this is necessary, the doctor will remove a small piece of muscle tissue and then the tissue sample is examined under a microscope. If you have the disease, the sample of muscle tissue will display some rather large fibers and they will also show a breaking down of other fibers in the sample. Genetic testing can also be performed.
There is currently no known cure for muscular dystrophy.
Inactivity (such as bed-rest and even sitting for long periods) can worsen the disease.
Physical therapy, Occupational therapy, speech therapy and orthopedic instruments (e.g., wheelchairs, standing frames) may be helpful. Physical therapy to prevent contractures (a condition when an individual with a muscular dystrophy grows and the muscles don't move with the bones and can be slowed down and/or make the individual's body straighter by daily physical therapy), orthoses (orthopedic appliances used for support) and corrective orthopedic surgery may be needed to improve the quality of life in some cases.
The cardiac problems that occur with Emery-Dreifuss muscular dystrophy and myotonic muscular dystrophy may require a pacemaker.
The myotonia (delayed relaxation of a muscle after a strong contraction) occurring in myotonic muscular dystrophy may be treated with medications such as quinine, phenytoin, or mexiletine but no actual long term treatment has been found.
Steroids are used to slow the disease progression, but long term or high doses of steroids can cause serious problems and they do not affect the final outcome.
The identification of the actual genes that are responsible for the various types of the disease has led to very extensive research on both gene and molecular therapy, but at the present time, all such treatments are still experimental. The use of Genetic counseling is highly recommended for families of affected individuals to determine if there are other family members who carry the defective gene so that the can participate in prenatal testing.
Some of the on going research involves trying to correct the defective genes so they will make the right proteins. Others are trying to produce chemicals that will function like the proteins in the body. They hope that either approach will help the muscles to perform and work properly. In addition, significant headway is being made with antisense oligonucleotides.
Muscular Dystrophy Prognosis
The prognosis for people with muscular dystrophy varies according to the type and progression of the disorder. Some cases may be mild and progress very slowly over a normal lifespan, while others produce severe muscle weakness, functional disability, and loss of the ability to walk. Some children with muscular dystrophy die in infancy while others live into adulthood with only moderate disability. The muscles affected vary, but can be around the pelvis, shoulder, face or elsewhere. Muscular dystrophy can affect adults, but the more severe forms tend to occur in early childhood. In some cases a person with a muscle disease will get progressively weaker to the extent that it shortens life span due to heart and breathing complications. However, some of the muscle diseases do not affect life expectancy at all.
There is a tremendous amount of ongoing research to find cures and treatments to slow muscle weakness. There is also a lot of research to learn how best to manage the breathing and heart issues which generally impact lifespan more than the muscle weakness.
Associated Sub-Topics and Pertinent Documents
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- 1 - FDA Approves First Drug to Treat Duchenne Muscular Dystrophy | U.S. FDA | 2016/09/20
- 2 - How Do I Know My Muscular Dystrophy Drugs are Working | DOE/Pacific Northwest National Laboratory | 2014/10/31
- 3 - STAT3 Inhibitor Key to Making New Muscles | Sanford-Burnham Medical Research Institute | 2014/09/07
- 4 - Potential New Duchenne Muscular Dystrophy Treatment | Children's Hospital Boston | 2011/03/19