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
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.
” Other names LGMD2B; Muscular dystrophy, limb-girdle, type 3; LGMD3 There are two major groups of LGMDs. Called LGMD1 and LGMD2, these two groups are classified by the respective inheritance patterns: autosomal dominant and autosomal recessive. If one copy of the abnormal gene is sufficient to cause the disease, it is said to be autosomal dominant; if two copies are needed, then the inheritance pattern is autosomal recessive. In some families, the inheritance pattern cannot be determined.
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
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.
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 DYSFgene, so he or she is not a carrier and is not affected with the disease
Limb-girdle muscular dystrophy (LGMD) is typically suspected when a person develops muscle weakness and wasting in the legs and arms, usually in the areas closest to the hips and shoulders, but not elsewhere in the body. However, it is hard to diagnose which type of LGMD a person may have without further testing. The doctor may wish to take a thorough personal and family history and to run some laboratory tests. These tests may include:
- Electromyography (EMG)
- Creatine-kinase levels
- Muscle biopsy
- Immunoblotting to determine if the dysferlinprotein is present at typical levels
Genetic testing of the DYSF gene may be ordered to confirm the diagnosis of LGMD2B and to help identify family members who are carriers of the disease.
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.
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 controlto 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.