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Facts About Myopathies Dear Friends: Hen I Was in My Early Teens, WI Was Having an Ice Cream at the Mall with Some Friends, and Suddenly I Couldn’T Move a Muscle

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Facts About Myopathies Dear Friends: Hen I Was in My Early Teens, WI Was Having an Ice Cream at the Mall with Some Friends, and Suddenly I Couldn’T Move a Muscle Facts About Myopathies Dear Friends: hen I was in my early teens, WI was having an ice cream at the mall with some friends, and suddenly I couldn’t move a muscle. The paramedics and the fire department came, and I had to be wheeled out on a stretcher. The doctors, my parents and friends were baffled by what had happened. Many of the doctors Christine Swanson, with her doubted there was anything wrong husband, Scott, and their children, with me. I had similar attacks over Anna and Nathan, on the Oregon the years. Finally, it was found Coast. that I had hyperkalemic periodic that your disorder wasn’t paralysis, one of the myopathies caused by anything you described in this booklet. or your parents did, and you didn’t catch it from If you’ve recently found out you anyone. As this pamphlet have an inheritable myopathy, you explains, each inheritable understand what my family and I myopathy is caused by a went through. Because of the rar- very uncommon genetic ity of these diseases, your primary defect that people often physician may not be aware that don’t even know they have. many of these myopathies can (Two of the myopathies be managed with medication or aren’t inheritable; they’re changes in diet and exercise. This caused by thyroid imbal- is why it’s very important that you ances that can occur for no get all the information you can known reason.) about your disorder. This booklet will help you get started. I’ve had to make many adjustments to living with Learning that you or your child has my myopathy. I know a rare myopathy can be frighten- what foods and activities ing and confusing. Some people can trigger an attack. With may think you’re lazy or mentally a balanced diet keeping unbalanced, and that can hurt. my potassium down and One thing you can be sure of is my body hydrated, I can 2 Facts About Myopathies • MDA exercise and live a full life. Computers and other technological I have a career as a legal advances help us to move around, assistant and a supportive communicate and work. husband who’s knowledge- able about my hyperKPP, “MDA is Here to Help You,” on and we have two healthy page 26, tells of the Association’s children. These victo- services. MDA is also the world ries were possible with leader in research on neuromus- the assistance of caring cular diseases, and its scientists doctors I found through have made many discoveries about the Muscular Dystrophy myopathies in recent years. Association. MDA also has This booklet will give you the provided endless support basic facts about the inherited and and information. endocrine myopathies, and MDA Like my hyperKPP, many will help you answer all your ques- myopathies can be con- tions as they arise. As you face the trolled so that they cause challenges ahead, please be assured very little limitation on that we’re making rapid progress your life. But, if you have toward better treatments and a one of the myopathies that cure. And remember, you’re not has more disabling effects, alone. you can be sure that MDA is your best ally — help- ing you to find appropriate Christine (Feigert) Swanson therapists, and to locate Portland, Oregon and purchase important assistive devices. And today, people with disabilities have many opportunities to develop and use their abilities. Federal law guarantees us a public education, equal employment opportunity and access to public places. Facts About Myopathies • MDA 3 What are Myopathies? he word myopathy means T“disease of muscle.” More spe- cifically, myopathies are diseases that cause problems with the tone and contraction of skeletal muscles (muscles that control voluntary movements.) These problems range from stiffness (called myotonia) to weakness, with different degrees of severity. Some myopathies, espe- cially when they’re present from birth, have life- threatening complica- tions. But, with time and physical therapy, some people born with myop- athies can gain muscle strength. Others often can manage their symptoms through medication, lifestyle modi- fications, or use of orthopedic and respiratory equipment. This booklet focuses on the six types of inherited myopathy (a Myopathies can myopathy that can be passed from cause weakness parent to child) in MDA’s program. or stiffness in all of the body’s vol- • myotonia congenita (Thomsen untary muscles. disease and Becker type) Because muscles support the body’s • paramyotonia congenita posture, severe muscle weakness (Eulenberg disease) can lead to skel- etal deformities. 4 Facts About Myopathies • MDA • periodic paralyses information on how myopathies (hyperkalemic, hypokalemic, are inherited, see “Does It Run in the Andersen-Tawil syndrome) Family?” page 10.) • central core disease/ In the inherited myopathies, genetic malignant hyperthermia mutations cause defects in various susceptibility proteins necessary for muscle tone and contraction. • nemaline myopathy (rod body disease) What are muscle tone and • centronuclear myopa- contraction, and what thies, including myotubular controls them? myopathy Contraction is the forceful shortening This booklet also contains or tightening of muscle, which pulls information on two nonin- on the joints to cause movement. herited myopathies caused by In other words, when your brain abnormal activity of the thy- “tells” a muscle to move, you cause roid gland — hypothyroid it to contract, and it’s then able to do myopathy and hyperthyroid what you’re asking. myopathy (see “Endocrine Myopathies,” page 20). Muscle tone refers to a readiness for contraction that makes resting mus- What causes cle resistant to stretching. A toned muscle holds its shape and elasticity the inherited and is able to respond by contracting myopathies? when you want it to move. Bodies with poor muscle tone appear “flop- These inherited myopathies py.” Good muscle tone is important are caused by mutations, for posture and coordination. or changes, in genes — the blueprints for making pro- A skeletal muscle’s tone and contrac- teins that are necessary for tion depend on its ability to respond our bodies to function cor- to stimulation from nerve cells, rectly. Genes are responsible which relay signals from the brain, for building our bodies; such as the decision to move your we inherit them from our hand or leg. A muscle is actually a parents — along with any bundle of individual muscle cells, mutations or defects they and a cluster of muscle cells stimu- have — and pass them on lated by a single nerve cell is called a to our children. (For more motor unit. Facts About Myopathies • MDA 5 The process of muscle contrac- at opposite ends by scaf- tion begins when the nerve cells folds called z-discs. When release chemical signals onto the the filament proteins slide muscle cells. These signals cause past each other — in a the opening of ion channels, pores ratchet-like mechanism that in each muscle cell’s outer surface is fueled by cellular energy that open and close to regulate the sources — they cause short- movements of charged atoms called ening of the muscle cell and ions. Different types of ion channels shortening (contraction) of allow specific ions — sodium, cal- the whole muscle. cium, potassium or chloride — to pass into and out of the muscle cell, Filament Proteins creating Z-Disc 4 electrical currents. Opening of sodium Calcium and cal- cium channels 3 Nerve causes an electrical Muscle Cell Cell excitation that leads to contrac- 1 Nucleus tion, while opening of potassium and chloride channels keeps the excitation from occurring. 2 The purpose of the electrical excitation is to rapidly spread Ion Channels the signal to contract through- out the entire muscle cell, and to A muscle cell is stimulated to contract stimulate the opening of still more by chemical signals sent from an adjoin- channels that release calcium from ing nerve cell (1). Those signals open internal compartments in the ion channels at the muscle cell’s surface, causing an inward/outward flow of ions muscle cell. that acts as an electrical current (2). Inside the muscle cell, the current spreads Finally, the freed calcium ions and causes opening of ion channels that trigger muscle contraction by line calcium storage compartments, stimulating the sliding action of releasing the calcium ions trapped within . These rodlike (3). The freed calcium ions trigger nearby filament proteins filament proteins to slide past each other, proteins run lengthwise within pulling the Z-discs closer together and the muscle cell and are anchored shortening the muscle cell (4). 6 Facts About Myopathies • MDA If this process is disrupted ment proteins. When the filament at any stage between the proteins fail to do their jobs, mus- nerve’s signaling the muscle cles can’t contract properly, causing and the filament proteins’ a loss of tone and strength. action, the muscle loses its normal capacity for tone At least one myopathy (a type of and contraction. At one myotubular myopathy) is caused extreme, the muscle might by mutations in a muscle pro- be limp and weak, and tein required for normal muscle at the other extreme, the development. When this protein is muscle may be involuntarily absent or inactive, the muscles don’t active and unable to relax. form properly. Some of the inherited myopathies What goes wrong are congenital, meaning they cause in inherited problems from the time of birth. myopathies? Others have a later onset, with symptoms appearing in childhood Many of the inherited or adulthood. myopathies are caused by mutations that interfere Myopathies aren’t contagious, and with ion channels, caus- they aren’t caused by overexertion. ing either too much or too However, exercise can aggravate little current from flowing some of the myopathies, because through the muscle cells.
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