What is Distal Muscular Dystrophy?
Distal muscular dystrophy (DD) is a group of inherited diseases that cause muscle weakness and deterioration. DD primarily affects the muscle of the extremities (distal muscles), and the lower legs and arms are the most common sites for symptoms.
The genetic mutations that cause DD are present at birth, but the disease symptoms usually don’t emerge until adulthood. DD is also sometimes called distal myopathy.
Muscular dystrophy (MD) is a collective term that refers to a collection of more than 30 diseases. The common characteristic of all the diseases is that they cause muscle weakness and a progressive loss of muscle tissue. Unfortunately, there is no known cure for these diseases, including DD.
Symptoms of Distal Muscular Dystrophy
Symptoms of DD usually appear first in adulthood and get progressively worse. Symptoms vary in severity from case to case, and not all people with DD will have the same symptoms.
Symptoms of DD can include:
- Muscle weakness and loss of muscle mass
- Weakness in the feet or legs that causes walking difficulties
- Weakness in the hands that affects grip strength
- Difficulty speaking
- Problems with swallowing
Types of Distal Muscular Dystrophy
DD can be categorized into several different types depending on the gene mutation that causes the disease. Types of DD include:
- Welander distal myopathy is a slow-progressing type that usually emerges after age 40 and causes weakness in the hands, feet, fingers, and toes. The heart may also be affected.
- Udd distal myopathy generally affects the ankles and shins, and muscle deterioration may eventually spread to the upper legs.
- Miyoshi myopathy often emerges in adolescence or early adulthood with weakness that begins in the calves.
- Hereditary inclusion-body myopathy type 2 typically affects the feet and thighs.
- Nonaka distal myopathy typically affects the shins before spreading to the upper legs, arms, and neck.
- Distal myopathy with vocal cord and pharyngeal signs is a rare type that affects the hands, feet, throat, and vocal cords.
What Causes Distal Muscular Dystrophy?
Muscular dystrophy occurs when the body cannot produce the proteins needed to build and protect muscle cells. Genes control the production of these proteins, and each type of MD is characterized by a gene abnormality that causes the abnormal production of a particular protein.
In the case of DD, an abnormal change (mutation) in one of several different genes interferes with the production of key proteins needed for the development and health of muscle cells. The lack of proteins causes muscle cells to be especially susceptible to damage and death.
Is Distal Muscular Dystrophy Hereditary?
All forms of DD are inherited disorders. Most types of DD are inherited in an autosomal dominant pattern, meaning that children may develop the disorder if they inherit even one copy of the mutated gene from either of their parents. If a parent carries the disorder-causing mutation, they will have a 50 percent chance of having an affected child with each pregnancy.
Some types of DD, including Myoshi distal myopathy and Nonaka distal myopathy, are inherited in an autosomal recessive pattern. This means a child must inherit two copies of the gene mutation, one from each parent, to develop the disorder. People with only one copy of the mutated gene will not develop DD but will be carriers who can pass the mutation on to their children. Two carrier parents have a 25 percent chance of having a child with DD with each pregnancy. Half of their pregnancies will produce a carrier, and a quarter of the pregnancies will produce a child with no mutated genes.
How Is Distal Muscular Dystrophy Detected?
Possible signs of DD include:
- Difficulty lifting your feet
- Dragging your feet while walking
- Difficulty raising your knees to walk
- Difficulty doing tasks, such as holding a pen or typing, requiring grip strength or finger dexterity
How Is Distal Muscular Dystrophy Diagnosed?
If a doctor is presented with symptoms that look like those of muscular dystrophy, they will begin the diagnostic process by conducting a physical exam and gathering a medical history. If it appears that a muscle disease is likely, several different tests can help determine if there is a muscle problem and which disease is the cause.
Possible diagnostic tests include:
- Creatine kinase (CK) test. Creatine kinase (CK) is a type of protein called an enzyme. CK in the blood is normal, but higher enzyme levels are created when muscles are damaged. When there is no apparent muscle injury, an elevated CK level can show the presence of a muscle disease like DD.
- Electromyography. This test uses an electricity-sensing needle probe to measure muscle function. The test can detect muscle abnormalities that could be a sign of DD.
- Muscle biopsy. This test involves removing and examining a small amount of muscle tissue. A biopsy may be able to detect muscle abnormalities caused by DD.
- Imaging exams. Imaging exams such as magnetic resonance imaging (MRI) or computerized tomography (CT) may detect the deterioration of muscles.
- Genetic testing. These blood tests look for the specific genetic abnormalities responsible for different types of DD.
PLEASE CONSULT A PHYSICIAN FOR MORE INFORMATION.
How Is Distal Muscular Dystrophy Treated?
There is no cure for DD, and no treatment will reverse the progression of its symptoms. With treatment, symptoms can sometimes be managed to help prevent severe, life-threatening complications. Possible treatment options include:
- Physical therapy
- Mobility aids such as braces or wheelchairs
- Respiratory therapy or breathing assistance
- Speech therapy
How Does Distal Muscular Dystrophy Progress?
DD symptoms typically progress slowly after symptoms first emerge, and the progression of symptoms can vary depending on the type of DD and from individual to individual.
Potential complications of DD include:
- Limited mobility. Muscle weakness can make it hard to get around, and some people with DD eventually lose the ability to walk.
- Respiratory problems. In rare cases, the muscles responsible for controlling breathing can be affected, making it difficult for people to breathe normally.
- Swallowing problems. Muscles that control the swallowing reflex can be affected by some types of DD. Swallowing difficulties can also lead to the aspiration of food or liquids into the lungs, leading to potentially fatal respiratory infections.
- Heart problems. Some types of DD may cause progressive damage to the heart muscle, and this heart damage can result in life-threatening complications.
How Is Distal Muscular Dystrophy Prevented?
There is no known way to prevent DD in someone born with a genetic mutation responsible for the disease. Parents with a family history of the disorder or who have had another child with DD are advised to consult a genetic counselor to assess their risk if they plan to have another child.
Distal Muscular Dystrophy Caregiver Tips
Studies have shown that caring for someone with muscular dystrophy can significantly negatively impact the caregiver’s life. Caregivers are at risk for depression, sleep problems, stress, anxiety, relationship problems, and low self-esteem.
Because of these risks, caregivers must take advantage of support systems to keep themselves healthy. The Muscular Dystrophy Association maintains a collection of resources for caregivers that includes educational resources, guides, and links to caregiver networks and support groups.
Many people with MD also suffer from other brain-related issues, a condition called co-morbidity. Here are a few of the disorders commonly associated with DD and other forms of MD:
Distal Muscular Dystrophy Brain Science
The most apparent effects of muscular dystrophy occur in the muscles, but it’s not uncommon for MD sufferers to also have cognitive or mental health problems. This suggests that MD can also affect the brain. Researchers are trying to understand how abnormalities in protein production that weaken muscles might harm brain development or function.
- The genetic mutation that causes myotonic MD produces a toxic chemical that damages muscle tissue. But symptoms of myotonic MD also often include memory, cognitive, and behavioral problems, leading scientists to suspect that the toxic chemical might also damage the brain. Studies have shown that the chemical is present in myotonic MD patients’ brains, and animal studies have shown that the chemical could produce neurological symptoms.
- People with Duchenne MD (DMD) often suffer from cognitive limitations and psychological disorders such as attention-deficit/hyperactivity disorder (ADHD) or obsessive-compulsive disorder (OCD). Dystrophin, the protein impacted by DMD, is also present in the brain, but scientists are not yet sure what it does there. Even though the protein’s role in the brain is still unknown, one study has linked dystrophin deficit with changes in brain development and a higher risk of cognitive problems.
These research areas could be the first steps in understanding the neurological impact of MD, and a broader understanding could lead to more effective treatments.
Distal Muscular Dystrophy Research