What is the definition of Limb-Girdle Muscular Dystrophy Type 2B?
Limb-girdle muscular dystrophy type 2B (LGMD2B) is one type of limb-girdle muscular dystrophy. These diseases affect the voluntary muscles, which are the muscles that are moved on purpose, such as the arms, legs, fingers, toes, and facial muscles. Specifically, LGMD2B is a slowly progressive disease that causes muscle weakness and wasting (atrophy) of the pelvic muscles and muscles of the shoulder girdle. People who are Jewish, and specifically those of Libyan Jewish descent, are more likely to have LGMD2B.
LGMD2B is caused by variations (also known mutations) in the DYSF gene. The disease is inherited in an autosomal recessive manner. Diagnosis of LGMD2B is suspected in people who have signs and symptoms of the disease, and the diagnosis can be confirmed by a muscle biopsy and genetic testing. While there are no treatments that can reverse the muscle weakness associated with the disease, supportive treatment can decrease complications.
What are the alternative names for Limb-Girdle Muscular Dystrophy Type 2B?
- Muscular dystrophy, limb-girdle, type 3
What are the causes for Limb-Girdle Muscular Dystrophy Type 2B?
Limb-girdle muscular dystrophy type 2B (LGMD2B) is caused by changes to the DYSF gene. When a genetic change causes a disease, it is also known as a pathogenic variation. The DYSF gene provides instructions to make a protein called dysferlin. Dysferlin is found in the thin membrane (sarcolemma) that surrounds muscle fibers. Scientists believe dysferlin is involved in repairing muscle fibers damaged naturally through use and may also be involved in the control of muscle inflammation. When there is a pathogenic mutation in the DYSF gene, the instructions to make dysferlin are not correct, which means the protein is either not made at all or the protein that is made cannot do its job properly. Without working dysferlin, the muscles are not able to repair themselves correctly and may become inflamed too easily leading to further damage to the muscle. Over time, this leads to the muscle weakness and wasting associated with LGMD2B.
What are the symptoms for Limb-Girdle Muscular Dystrophy Type 2B?
Limb-girdle muscular dystrophy type 2B (LGMD2B) causes muscle weakness and wasting (atrophy) of the muscles of the pelvis and shoulder girdle. The muscle weakness can cause an inability to tiptoe and difficulty walking and running. In some cases, people with the disease may have enlarged (hypertrophic) calf muscles. The disease is slowly progressive, meaning the muscle weakness typically worsens over many years.
The symptoms of LGMD2B typically begin in adolescence or young adulthood. The age of onset ranges from 15 to 35 years, and the legs are usually the first part of the body affected. Symptoms that may be common in other types of limb-girdle muscular dystrophy, such as heart (cardiac) and breathing (respiratory) problems, are uncommon in people with LGMD2B. The signs and symptoms of people with LGMD2B can vary, even among members of the same family.
What are the current treatments for Limb-Girdle Muscular Dystrophy Type 2B?
Unfortunately, there is no cure for limb-girdle muscular dystrophy type 2B (LGMD2B). Treatment options that may be recommended for people with LGMD2B may include:
- Weight control to avoid obesity
- Physical therapy and stretching exercises
- Use of mechanical aids such as canes, walkers, and wheelchairs
It is recommended that people with LGMD2B be provided with social and emotional support to cope with the diagnosis. Other specialists that may be recommended include a neurologist, occupational therapist, nutritionist, and genetic counselor. No currently available medications can relieve or reverse the symptoms associated with LGMD2B. However, research is ongoing to try to determine if treatments such as gene therapy may be helpful in the future.
What is the outlook (prognosis) for Limb-Girdle Muscular Dystrophy Type 2B?
In general, limb-girdle muscular dystrophy type 2B (LGMD2B) is a slowly progressive disease, meaning the muscle weakness slowly continues to worsen. Eventually, most people with LGMD2B require a wheelchair, but this may be years after the diagnosis. Muscle weakness affecting the heart muscles or muscles necessary for breathing is uncommon in people with LGMD2B. In rare cases, the progression of the disease may be more rapid, with people requiring a wheelchair in one or two years after symptoms begin.
Is Limb-Girdle Muscular Dystrophy Type 2B an inherited disorder?
Limb-girdle muscular dystrophy type 2B (LGMD2B), and all subtypes of LGMD type 2, are inherited in an autosomal recessive manner. This means that people with LGMD2B have pathogenic variations
(changes, formerly known as mutations) in both copies of the DYSF gene in each cell of the body. We inherit one copy of each gene from our mother and the other from our father. People who have only one changed copy of the DYSF gene are known as carriers of the disease. Carriers of LGMD2B typically do not have any signs or symptoms of the disease. When two carriers of LGMD2B have children, each child has a:
- 25% chance to have LGMD2B
- 50% chance to be a carrier of LGMD2B like each parent
- 25% chance to have inherited two working copies of the DYSF gene, so he or she is not a carrier and is not affected with the disease