Limb-Girdle Muscular Dystrophy includes a group of diverse disorders which affect the voluntary muscles, predominantly around the person's pelvic and shoulder areas. On occasion the person's heart and breathing muscles may be involved as well. Various types of LGMD differ in their severity, the age at which onset occurs, and the manner in which they are inherited. The type of genetic alteration involved is the reason for the variation.
Limb-Girdle Muscular Dystrophy (LGMD)
Limb-Girdle Muscular Dystrophy includes a group of diverse disorders which affect the voluntary muscles, predominantly around the person's pelvic and shoulder areas. On occasion the person's heart and breathing muscles may be involved as well. Various types of LGMD differ in their severity, the age at which onset occurs, and the manner in which they are inherited. The type of genetic alteration involved is the reason for the variation. A person's genetic, 'blueprint,' is comprised of thousands of different genes containing information required to produce specific proteins.
The genes within a person may become altered through mutations which happen in the sequence of chemical structures referred to as, 'Nucleotides,' which are represented by four letters; 'A','T,' 'C,' and, 'G.' These Nucleotides make up the genes in question. Mutations involving these genes may cause various forms of LGMD; so can different changes within the same gene. Differences within a gene may lead to either milder or more severe forms of LGMD. At this time, scientists have identified around fifteen different genes which can be altered and cause LGMD; they are working to locate additional genes.
Symptoms of LGMD
Onset of LGMD might involve the person's shoulder area, their pelvis, or both. Symptoms that may arise early involve difficulty with walking or running, as well as getting up from the floor. Commonly as well as eventually, the person affected will experience difficulty with climbing stairs, as well as standing up from a squatting position to walk. The person may experience muscle weakness in their shoulders that makes it difficult to raise their arms above their head, hold their arms outstretched, or carry objects which are heavy. Fortunately, the person's brain, intellect and senses do not experience impairment. On rare occasion, some forms of LGMD may involve the person's heart muscle and cause symptoms of heart failure, or rhythm disturbance. There are some less common forms of LGMD which may affect the person's respiration, potentially resulting in headaches, sleepiness, or a lack of energy. Respiratory and heart symptoms can be difficult to recognize and breathing and heart systems in persons affected with LGMD need to be monitored in order to detect any changes.
Progression of LGMD
LGMD is progressive, meaning that persons affected with this disability have muscles which continue to become weaker throughout their lives. Due to the wide range in severity of the various LGMD's, the rate of progression among them varies. Over a period of time persons with LGMD lose both strength and muscle mass. The muscles that are involved can present various levels of weakness between the person's left and right sides; weakness the person experiences may also extend to neighboring muscles.
If the rate at which the progression moves is slow and unnoticeable, the person experiencing LGMD may appear to suddenly worsen should a loss of function occur. To provide an example - a person has not noticed their rate of progression until they have found they are unable to rise from a chair or raise an arm in order to brush their hair. The person has not noticed the progression of LGMD until their strength has fallen below the level required to accomplish a task. This phenomenon is referred to as the, 'Stair Step,' during which progression of the disease appears to cease for a period of time, then worsens suddenly.
Progression of LGMD appears to be rather rapid during childhood, when onset of the disease occurs. Children experience an increase in body weight and size, as well as an increase in muscle weakness. As they become adults, their body growth ceases, and weakness only increases as the person's muscles break down. Due to the variable nature of LGMD it is not possible at this time to predict the course the disease will take in the majority of the persons affected.
Inheritance of LGMD
A faulty gene, passed from either one or both parents to a child, causes inheritance of LGMD. A person may inherit LGMD in two ways; either Autosomal or Dominant recessive. Two copies of the gene are always present; one from the person's father, and another from the person's mother. Should a single copy of a gene mutation occur, causing LGMD, it is referred to as, 'Dominant.' 'Recessive,' form of LGMD occurs when a mutation has been passed from both parents, and no normal gene copy is present. Dominant forms of LGMD may occur through a new mutation in the person affected, or may be inherited from a parent who is affected. Inherited Autosomal Dominant traits require only one affected parent in order to transmit a gene mutation. The chance is fifty-fifty that a child of an affected parent, whether that child is male or female, will inherit LGMD.
Autosomal Recessive traits which are inherited involve children who have received an altered gene from both of their parents. In the majority of cases each of the parents carries the gene. What this means is that each of the parents carries the gene, yet are not affected and do not show any symptoms - the other copy of the gene they carry is normal. Children of either sex born to these parents have a twenty-five percent chance of having LGMD, a fifty-percent chance of becoming a carrier of it, and a twenty-five percent chance of carrying two normal gene copies.
With Recessive disorder, should one parent be affected and present symptoms, it means that both of their gene copies are altered. An affected parent will pass the gene on to any children they have. The chances are, except in rare cases, that the other parent will have two normal gene copies. In this case, the parents would have children who would be carriers of LGMD, yet not be affected by it.
Improved testing for use in diagnosing LGMD is under development. LGMD has physical symptoms that are similar to other neuromuscular disorders like Becker's Muscular Dystrophy, making a diagnosis of LGMD a process of elimination after other potential causes for weakness in the person's hips and shoulders have been identified. Prior to lab testing, the person's medical history is taken, as well as a physical examination, in order to determine the pattern of weakness the person is experiencing. A blood test referred to as a, 'CK Test,' is performed early in the diagnostic process. 'CK,' stand for, 'Creatine Kinase,' an enzyme which leaks out of damaged muscle tissues. Should the test reveal increased levels of Creatine Kinase, it is suggestive that the person's muscles are themselves the likely cause of the weakness they are experiencing. The CK test is unable to identify the specific disorder the person has that is affecting their muscles.
Lab exams could be conducted in order to find evidence of any general changes related to muscle weakness or changes the person is experiencing. At times, a test referred to as an, 'Electromyography,' is performed in order to find the location of the weakness experienced. The test measures electrical activity within muscle cells. A muscle biopsy, during which a sample of muscle tissue is taken for examination, may be performed as well. The sample can help to find underlying causes of muscle weakness. DNA testing may be pursued in order to determine the specific type of LGMD the person has. Muscle stains may be used in order to identify the precise protein that is missing. The techniques mentioned have not been perfected yet, or shown to be one-hundred percent accurate where providing information about the exact type of LGMD a person has is concerned.
Managing Symptoms of LGMD
Persons affected by LGMD find that a well-balanced diet combined with moderate exercise may assist in reducing or controlling weight. Low-resistance exercise, swimming, and water aerobics can help to facilitate greater mobility. Occupational and physical therapies, as well as assistive devices, can help to enhance and maintain flexibility and mobility. Persons with LGMD should keep walking for as long as they are able; this may involve using a scooter or wheelchair for longer distances and saving strength for short walks. Sometimes, joint deformities prevent some forms of exercise, physiotherapy, orthoses, and surgery. In order to avoid spinal instability, appropriate seating and back support should be maintained.
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