Limb-Girdle Muscular Dystrophy
What is LGMD?


Overview


Limb-girdle muscular dystrophy (LGMD) is a group of diseases that cause weakness and wasting of the muscles in the arms and legs.

  • The muscles most affected are those closest to the body (proximal muscles), specifically the muscles of the shoulders, upper arms, pelvic area, and thighs.  Eventually, however, all skeletal muscles are affected.

    The severity, age of onset, and features of LGMD vary among the many subtypes.  Signs and symptoms may first appear at any age and generally worsen with time, although in some cases they remain mild. However, within each LGMD subtype, the severity, age of onset, and features demonstrate a high degree of consistency.  

    In the early stages of LGMD, affected individuals may have an unusual walking gait, such as waddling or walking on the balls of their feet, and may also have difficulty running. They may need to use their arms to press themselves up from a squatting position because of their weak thigh muscles. As the condition progresses, people with LGMD eventually require wheelchair assistance.

    Muscle wasting may cause changes in posture or in the appearance of the shoulder, back, and arm. In particular, weak shoulder muscles tend to make the shoulder blades (scapulae) “stick out” from the back, a sign known as scapular winging. Affected individuals may also have an abnormally curved lower back (lordosis) or a spine that curves to the side (scoliosis). Some develop joint stiffness (contractures) that can restrict movement in their hips, knees, ankles, or elbows. Overgrowth (hypertrophy) of the calf muscles occurs in some people with LGMD.

    Weakening of the heart muscle (cardiomyopathy) occurs in some forms of LGMD, most notably the sarcoglycanopathies (LGMD2C, LGMD2D, LGMD2E, and LGMD2F) and dysferlinopathy (LGMD2B). Some affected individuals experience mild to severe breathing problems related to the weakness of muscles needed for breathing. In some cases, the breathing problems are severe enough that affected individuals need to use a machine to help them breathe (mechanical ventilation).  Death resulting from cardiopulmonary insufficiency can occur before age 30 in some subtypes.

    Intelligence is generally unaffected in LGMD.

  • The various forms of LGMD are caused by mutations in many different genes. These genes provide cells with instructions for making proteins that are involved in muscle maintenance and repair.

    Some of the proteins produced from these genes assemble with other proteins into larger protein complexes. These complexes maintain the physical integrity of muscle tissue and allow the muscles to contract. Other proteins participate in cell signaling, cell membrane repair, or the removal of potentially toxic wastes from muscle cells.

    Most forms of LGMD are inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.  Autosomal recessive forms of LGMD are known as Type 2 forms, characterized by having a numeral two in their names, e.g. LGMD2B.  

    Several rare forms of LGMD are inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Autosomal dominant forms of LGMD are known as Type 1 forms, characterized by having a numeral one in their names, e.g. LGMD1B.

  • After carefully evaluating a patient’s medical history, the doctor will perform a thorough physical exam. If muscular dystrophy (MD) is suspected, there are a variety of laboratory tests that can be used to confirm the diagnosis. These tests may include:

    Blood tests: When blood tests are performed to test for MD, the doctors are looking for an enzyme called creatine kinase (CK). Elevated CK level is noted when there is muscle damage and is a very helpful marker for MDs.

    Electromyogram (EMG): EMG is a test that measures the muscle’s response to stimulation of its nerve supply (nerve conduction study) and examines the electrical activity of muscles (needle electrode examination). This test is very helpful in demonstrating that the weakness is due to a muscle disease rather than a nerve disease.

    Muscle biopsy: During a muscle biopsy, a small piece of muscle tissue is removed, sent to a pathology lab for specific staining, and then examined under a microscope. If MD is present, changes in the structure of muscle cells and the findings on different immunohistochemical stainings can help with the diagnosis of MDs.

    Genetic testing: Many MDs can be definitively diagnosed by testing for the mutated genes. In many instances, this is the most specific test to diagnose MDs. If clinical features and family history point to specific types of MDs, neuromuscular specialists might directly go to genetic testing and skip muscle biopsy. This approach is common in LGMDs.


LGMD Treatment


There is currently no cure for LGMD. For the time being, treatment is aimed at preventing complications caused by:

Muscle weakness

Decreased mobility

Contractures

Scoliosis

Heart defects

Respiratory insufficiency

Care is focused on physical therapy, occupational therapy, surgery to correct musculoskeletal complications, cardiac care, and respiratory care.