Limb-girdle muscular dystrophies (LGMD) are a group of rare progressive genetic disorders that are characterized by wasting (atrophy) and weakness of the voluntary muscles of the hip and shoulder areas (limb-girdle area). Muscle weakness and atrophy are progressive and may spread to affect other muscles of the body. Many different subtypes have been identified based upon abnormal changes (mutations) of certain genes. The age at onset, severity, and progression of symptoms of these subtypes may vary greatly from case to case, even among individuals in the same family. Some individuals may have a mild, slowly progressive form of the disorders; other may have a rapidly progressive form of the disorder that causes severe disability.
The term limb-girdle muscular dystrophies is a general term that encompasses several disorders. These disorders can now be distinguished by genetic and protein analysis. The various forms of LGMD may be inherited as autosomal dominant or recessive traits. Autosomal dominant LGMD is known as LGMD1 and there are currently recognized eight subtypes (LGMD1A-1H). Autosomal recessive LGMD is known as LGMD2 and has 17 subtypes (LGMDA-Q).
Additional terminology has been used in the past to describe forms of muscular dystrophy that are now classified under LGMD. These terms are no longer widely used and include scapulohumeral (Erb) muscular dystrophy, pelvifemoral (Leyden-Mobius) muscular dystrophy, and severe childhood autosomal recessive muscular dystrophy (SCARMD).
Although there are some common themes recognizable in the main types of LGMD, the age at onset, severity, and progression of symptoms associated with LGMD may vary greatly from case to case, even among members of the same family. Some cases of LGMD may have onset during adulthood, mild symptoms, and slow progression; others may have onset during childhood and early severe disability such as difficulty climbing stairs and walking. Some individuals eventually require a wheelchair. In most cases, childhood onset of LGMD results in a more severe disorder that progresses more rapidly than adolescent or adult onset cases.
The major symptoms of LGMD are progressive wasting (atrophy) and weakness of the proximal muscles of the hip and shoulder areas. Proximal muscles are the muscles that are closest to the center of the body such as the muscles of the shoulder, pelvis, and upper arms and legs. Muscle weakness may spread from the proximal muscles to affect distal muscles. Distal muscles are those farther from the center of the body and include the muscles of the lower arms and legs and the hands and feet.
Muscle weakness usually affects the muscles of the pelvic and hip area first and affected individuals may have difficulty standing from a sitting position or walking up stairs. Weakness of the hip and upper leg muscles may cause a distinctive waddling gait. Eventually, muscle weakness affects the muscles of the upper arms and shoulders (limb-girdle area). Consequently, affected individuals may have difficultly raising their arms over their heads or carrying heavy objects. Muscle weakness may be associated with soreness in the muscles and joint pain.
Additional abnormalities that may develop in individuals with LGMD include abnormal side-to-side curvature of the spine (scoliosis), abnormal front-to-back curvature of the spine (lordosis), thickening and shortening of tissue that cause deformity and restricts movement of affected areas, especially the joints (contractures), and overgrowth (hypertrophy) of certain muscles such as the calf muscle.
In some particular forms of LGMD, weakening of the heart muscle, known as cardiomyopathy, can occur. Cardiomyopathy is a progressive condition that may result in an impaired ability of the heart to pump blood; fatigue; heart block; irregular heartbeats (arrhythmias) and, potentially, heart failure. Heart abnormalities are not associated with all forms of LGMD.
The muscles of the respiratory system may also become involved in some cases resulting in difficulty swallowing (dysphagia), slurred speech (dysarthria), and breathing difficulties. Breathing difficulties may become progressively worse in such cases.
AUTOSOMAL RECESSIVE LGMD
At least 17 different forms of autosomal recessive LGMD have been identified. These disorders are characterized by progressive weakness of the muscles of the pelvic girdle, legs, arms and shoulders. Progression of muscle weakness may be slow or rapid and may vary even among individuals in the same family. Intelligence is normal. The age of onset varies from subgroup to subgroup. Overall, onset is more common in childhood but it may even occur late in adult life.
LGMD2A (calpain-deficient LGMD; calpainopathy)
This form of LGMD usually affects children between the ages of 8-15, but may range from 2-40 years of age. Most cases are characterized by muscle weakness affecting the hip-girdle area although the hip adductor muscles may be spared. Degeneration (atrophy) is prominent. Affected children may exhibit a distinct waddling gait and may fall frequently. They may also experience difficulty running and climbing stairs. Respiratory problems have been reported with this form of LGMD, but heart abnormalities have not been.
Onset of this form of LGMD is usually during the juvenile years. Most individuals have normal mobility during childhood. Muscle weakness affects muscles of both the pelvic and shoulder area, but usually progresses very slowly. Wasting (atrophy) of the calf muscle and an inability to walk on tiptoes may be seen early in the disease progression. In rare cases, temporary (transient) overgrowth of the calf muscle, painful swelling of the calf, and early development of contractures may occur. The heart and respiratory muscles are usually not affected.
LGMD2B is caused by mutations of a gene that also causes Miyoshi myopathy a rare muscle disorder characterized by weakness of the distal muscles of the legs and arms. Families have been reported in which some members develop LGMD2B and others Miyoshi myopathy. (For more information on this disorder, choose “Miyoshi” as your search term in the Rare Disease Database.)
These forms of LGMD may range from a severe form often with childhood onset to a mild form often with adult onset. The severity varies greatly even among individuals of the same family. Early onset forms may cause progressive muscle weakness of the legs, hips, abdomen, and shoulder. The progression of muscle weakness of the sarcoglycanopathies is often more rapid than with other forms of LGMD and affected individuals may need a wheelchair between 12-16 years of age. Individuals with later onset usually experience a slower progression and more mild symptoms. Such individuals usually retain the ability to walk independently late into adulthood.
Additional symptoms are often associated with the sarcoglycanopathies including overgrowth of the calf and tongue muscles, cardiomyopathy, respiratory abnormalities, contractures, and scoliosis.
This form of LGMD usually becomes apparent during childhood or adolescence and presents with muscle weakness of the upper and lower legs. Affected children may have difficulty climbing stairs and running. Affected individuals often need a wheelchair by the third or fourth decade. Heart abnormalities have occurred in approximately half of the reported cases. Overgrowth (hypertrophy) of the calf muscle may also occur.
LGMD2H (TRIM 32 mutations)
This form of LGMD has been reported in the Hutterite population of Manitoba, Canada. Affected individuals develop weakness of the lower limbs that may be mild or severe. Weakness of facial muscles may also occur. As the disease progresses, muscles of the arms may become involved. Affected individuals may remain able to walk well into adulthood.
LGMD2I (fukutin-related proteinopathy)
This form of LGMD may range from mild to severe. Early childhood onset of LGMD2I usually indicates a severe clinical course with affected individuals needing a wheelchair by the second decade. There is overlap with a congenital form of muscular dystrophy, MDC1C. In such cases, affected individuals have severe muscle weakness of both the arms and legs, loss of muscle tone (hypotonia), and delays in attaining motor milestones. The late or adult onset form of LGMD2I is a slowly progressive, mild form of the disorder. LGMD2I is also associated with cardiomyopathy and respiratory abnormalities.
This form of LGMD occurs when two titin gene mutations are present and has a variable age of onset ranging from 10-30 years. Affected individuals have severe progressive proximal muscle weakness. Eventually the distal muscles become involved and some individuals may require the use of a wheelchair. When only one titin gene mutation is present, distal myopathy can result. LGMD2J has been reported in Finnish individuals.
This extremely rare form of LGMD has been reported in Turkish individuals. Onset is during infancy or early childhood. Affected individuals display slowly progressive muscle weakness and most retain the ability to walk into late adolescence. All affected individuals had developmentaldelays.
Affected individuals were reported to have proximal muscle weakness in lower and upper limbs and muscle hypertrophy was common. Intelligence was reported to be normal.
Causative genes have been identified for LGMD2K, LGMD2L, LGMD2M, LGMD2N, LGMD2O, LGMD2Q and recessive LGMD with primary alpha-dystroglycan defect.
AUTOSOMAL DOMINANT LGMD
The autosomal dominant forms of LGMD occur less frequently than the autosomal recessive forms and are more likely to occur later during life. In many cases, autosomal dominant LGMD progresses at a slower rate than autosomal recessive LGMD and has symptoms can be variable, even among members of the same family. Each gene mutation can lead to many different groups of symptoms. Examples of some of the symptoms that can be associated with specific gene mutations are as follows:
The onset of LGMD1A varies, ranging from adolescence to adulthood. This form of LGMD is characterized by proximal muscle weakness sometimes associated with slurred speech (dysarthria) and an abnormally tight Achilles tendon. Muscle weakness in the arms may also occur. The distal muscles may eventually become involved as well. The progression of LGMD1A is extremely slow and only a few affected individuals eventually need a wheelchair. Heart involvement has been noted in some cases. This phenotype overlaps with the group of diseases known as myofibrillar myopathies, another heterogeneous group of muscle diseases, which may also be associated with myotilin mutations.
LGMD1B (lamin A/C)
This form of LGMD is characterized by slowly progressive proximal muscle weakness. Affected individuals may also develop overgrowth (hypertrophy) of calf muscles and mild contractures of the elbows or Achilles tendon. Heart abnormalities are frequent and should be screened for including progressive conduction defects that can ultimately lead to irregular heartbeats (arrhythmias) and heart block. Lamin A/C mutations can result in a wide range of different phenotypes so care is required to offer genetic testing in families known to be affected.
This form of LGMD is characterized by cramping muscle pain after exercise, mild to moderate proximal muscle weakness, and overgrowth of the calf muscle. Progression of muscle weakness may be slow or rapid. Onset is usually during early childhood. Patients may have so called rippling muscles.
This extremely rare form of LGMD is characterized by progressive muscle weakness that first affects the hip-girdle area before spreading to affect the limb-girdle area. Onset is usually during early adulthood, but may occur as late as the sixth decade. The progression of the disorder is slow. Heart defects including conduction abnormalities and dilated cardiomyopathy may occur. Individuals with this form of LGMD usually remain able to walk.
This form of LGMD is associated with progressive weakness of the proximal muscles of the upper and lower legs. Onset is usually during childhood and the progression of the disease is slow. Affected individuals may also develop difficulty swallowing (dysphagia) and contractures. Heart abnormalities occur in this form of LGMD usually one or two decades after development of muscle weakness.
Causative genes have not been identified for LGMD1E, LGMD1F, LGMD1G, or LGMD 1H.
Additional cases of LGMD have been reported in the medical literature that have not been linked to any of the abovementioned subtypes and for which no causative gene has been identified. This means that further LGMD genes probably still remain to be identified.
LGMD is a genetic disorder that is inherited as either an autosomal recessive or dominant trait. The autosomal recessive forms are estimated to account for 90 percent of cases. Genetic disorders are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child. In some cases, dominant genetic mutations may occur spontaneously for no apparent reason in families without a previous history of the mutation (sporadic mutation). This “new” mutation is then passed on as an autosomal dominant trait.
Researchers have identified many different subtypes of LGMD, each one resulting from a mutation of a different disease gene (genetic heterogeneity). The genes associated with many of these subtypes have been identified. Most of these genes are involved in the production of certain muscle proteins. These proteins may be located on the membrane surrounding each muscle cell or within the cell itself. The membrane surrounding each muscle cell, known as the sacrolemma, protects the cells from injury and serves as a gate that allows or prevents substances into the cell. If one of the proteins is missing or defective, muscle cells may be damaged or may incorrectly allow substances in or out of the cell, eventually resulting in the symptoms of LGMD. The exact role and function of all these proteins and how their deficiency or absence causes LGMD is not yet known.
The genes associated with the various types of LGMD are listed in the Gene table of monogenic neuromuscular disorders found in the following link:
LGMD affects males and females in equal numbers. The incidence of the disorder is unknown. The prevalence of LGMD is unknown, but estimates range from one in 14,500 to one in 123,000. The age of onset can vary greatly even among individuals of the same family. The relative frequencies of the different types of LGMD vary from population to population, but worldwide LGMD2G, 2H and 2J are extremely rare.
Within the LGMD group, it is important to reach a precise diagnosis so that the patient and his or her family may be given correct genetic advice, as well as appropriate guidance for the management of complications, which can vary from disease entity to disease entity. This particularly relates to the risk of cardiac or respiratory complications. The precise testing available today may make it possible for individuals who were given a presumed diagnosis of LGMD in the past to be reappraised and given a more precise molecular diagnosis.
A diagnosis of LGMD is made based upon a thorough clinical evaluation, a detailed patient history, identification of characteristic symptoms (e.g., specific distribution of muscle weakness and atrophy), and a variety of specialized tests including surgical removal and microscopic examination (biopsy) of affected muscle tissue that may reveal characteristic changes to muscle fibers; a test that assesses the health of muscles and the nerves that control muscles (electromyography); specialized blood tests; tests that evaluate the presence and number of certain muscle proteins (immunohistochemistry); and molecular genetic testing.
During an electromyography, a needle electrode is inserted through the skin into an affected muscle. The electrode records the electrical activity of the muscle. This record shows how well a muscle responds to the nerves and can determine whether muscle weakness is caused by the muscle themselves or by the nerves that control the muscles. An electromyography can rule out nerve disorders such as motor neuron disease and peripheral neuropathy and also neuromuscular junction disorders such as myasthenic syndromes some of which may present with limb girdle weakness. It will not allow the diagnosis of a specific LGMD subtype but can be useful to exclude alternative diagnoses.
Blood tests may reveal elevated levels of the creatine kinase (CK), an enzyme that is often found in abnormally high levels when muscle is damaged. Elevated CK levels occur in some, but not all cases of LGMD. CK levels are much higher in the autosomal recessive forms of LGMD than the autosomal dominant forms. The detection of elevated CK levels can confirm that muscle is damaged or inflamed, but cannot confirm a diagnosis of LGMD. It may however help to indicate which type of LGMD is more likely than others.
In some cases, a specialized test can be performed on muscle biopsy samples that can determine the presence and levels of specific muscle proteins within muscle cells. Various techniques such as immunostaining, immunofluorescence or Western blot (immunoblot) can be used. These tests involve the use of certain antibodies that react to certain muscle proteins. Tissue samples from muscle biopsies are exposed to these antibodies and the results can determine whether a specific muscle protein is present and in what quantity. Deficiency of certain muscle proteins indicates what form of LGMD is present. These protein tests are not available for all forms of LGMD, but can be used to test for LGMD2C-2F (the sarcoglycanopathies), LGMD1C (caveolinopathy), LGMD2B (dysferlinopathy) and some cases of LGMD2A (calpainopathy).
Molecular genetic testing involves the examination of deoxyribonucleic acid (DNA) to identify specific a genetic mutation. This is now the gold standard for diagnosis in LGMD and allows a specific diagnosis as well as specific testing for other family members.
No cure exists for any form of LGMD. Treatment is aimed at the specific symptoms present in each individual. Specific treatment options may include physical and occupational therapy to improve muscle strength and prevent contractures; the use of various devices (e.g., canes, braces, walkers, wheelchairs) to assist with walking (ambulation) and mobility; surgery to correct skeletal abnormalities such as scoliosis; and regular monitoring of the heart and the respiratory system for the development of such complications potentially associated with some forms of LGMD.
Genetic counseling may be of benefit for affected individuals and their families. Other treatment is symptomatic and supportive. Patients should be provided with contact details for the relevant patient organizations and registries.
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