Glossary

A rare autosomal recessive ataxia caused by problems with fat metabolism in the body and progressive neurological deterioration.  Symptoms of the disease include poor transmission of nerve impulses, muscle weakness, and degeneration of the retina leading to blindness.  A controlled diet is the typical way that this disorder is managed.   A physician may also prescribe vitamins to treat this disorder.

A chemical neurotransmitter produced by the body that is important for the movement of nerve impulses or signals between nerve cells, or between the nerve cell and the muscle fiber it supplies.

Describes a group of disorders that cause progressive weakness due to muscle inflammation.  The most common of these disorders are polymyositis, dermatomyositis, and inclusion body myositis.

Most genes exist in two copies (one in inherited from the mother, one from the father). Genes reside on chromosomes. There are 22 pairs of “regular” chromosomes, and one pair of “sex”-determining chromosomes (males are XY; females are XX). For each chromosome pair, there are a series of genes that are paired (one copy of each gene being present on one of the matched chromosomes). Since we inherit one copy of each chromosome from each parent (and thus one copy of each of the genes lined up on the chromosome), we end of with 2 copies, or alleles, of each gene. Alternate forms of the same allele produce variations in the characteristics of inheritance such as, for example, eye color or blood type. If the paired alleles are identical they are said to be homozygous, if they are different they are heterozygous.

See Amyotrophic Lateral Sclerosis

A building block of protein. Each protein consists of a specific sequence of amino acids. There are 20 types of amino acids that can make up proteins.

Also known as Lou Gehrig's disease and motor neuron disease. It is a rapidly progressive and fatal disease of the motor neurons in the spinal cord and lower brain that control the voluntary muscles throughout the body. As these motor neurons die, the ability of the brain to control muscle movement is lost. There is a progressive loss of motor functions. Speech and swallowing are often affected. Intellect is not affected. It can occur in either sex, usually first detected in middle to late adulthood. In most cases, the cause is unknown and at the present time, there is no treatment or cure.

Absence or lack of oxygen.

A type of nerve cell located in the spinal cord. Messages from the brain are transmitted down the spinal cord to the anterior horn cell, and then from the anterior horn cell down its’ axon which in turn forms part of the peripheral nerve that supplies muscle. (See Motor Unit)

Also known as immune bodies, antibodies are substances produced by the body to fight bacteria and viruses. For reasons that are not well understood, the body sometimes produces antibodies that attack it's own tissues and organs.

Drugs used to enhance the strength and endurance of weakened muscles. They may be used to augment muscle contractions in myasthenia gravis. Examples of these drugs include Neostigmine, and Physostigmine.

Difficulty or inability to swallow.

Total or partial loss of the ability either to use (expressive aphasia) or understand words (receptive aphasia).

Cessation of breathing.

A measure of the oxygen and AC carbon dioxide levels in the bloodstream.

A syndrome characterized by multiple joint contractures (fixed position of a joint) present at birth. In some children it is a non-progressive syndrome where muscles are poorly developed. In some cases, arthrogryposis is a feature of severe forms of congenital muscular dystrophy or congenital myopathy.

Inflammation of the lungs as a result of inhaling food particles or fluids.

Application of pressure to the abdomen to strengthen the cough.  The purpose of this procedure is to prevent some types of respiratory complications by helping to bring up secretions.  A person may be unable to these bring up on his or her own because of weakness.

Without discernible symptoms.

Poorly coordinated movements and unsteadiness. It results from a failure of the brain to regulate and co-ordinate posture and muscle movements.

A hereditary, progressive disease, transmitted as an autosomal recessive trait. In addition to ataxia, it is associated with vascular lesions of the skin and eye, frequent respiratory infections, abnormal movements of the eyes and immune system disorders.

A decrease in the size of a normally developed organ or tissue. It is often used in reference to wasting of tissue such as muscle where it loses strength and size.

A disease that is due to antibodies formed by the body against itself. In autoimmune disease, the body fails to differentiate between itself and foreign substances and reacts to the body's own material as though it were foreign.

In this type of inheritance pattern, a disorder typically appears in each generation, passed on by one parent of either sex who also has the disorder. Each child born to an affected parent has a 50% chance of inheriting the disorder and a 50% chance of being unaffected. There is no carrier status.

In order for the disorder to be expressed, each parent must be a carrier of an mutated copy of the same gene, and each must pass on that copy to his/her offspring. Each child born to parents who are carriers has a 25% chance of having the disorder (by inheriting the mutated copy from both parents), a 50% chance of being a carrier (by inheriting an mutated copy from one parent and a healthy copy from the other) and a 25% chance of inheriting a healthy copy of the gene from each parent.

Any of the 22 pairs of chromosomes found in the human body that are not involved in the determination of sex. They are identical in both males and females. Each pair of autosomes (one from the father, one from the mother) carries genes for the same traits.

A chronic, progressive X-linked recessive form of muscular dystrophy. Becker muscular dystrophy is due to mutations in the dystrophin gene. The mutation in the gene results in a reduced production of the dystrophin protein within muscle. Patients with mutations in the dystrophin gene that lead to complete absence of the dystrophin gene causes Duchenne muscular dystrophy. Symptoms are usually first noted in the early teens, and include clumsiness, difficulty running or walking up stairs and frequent falls.

Diagnosed at birth, this disorder is characterized by abnormal muscle tone only. The reflexes are normal and there is no evidence of muscle wasting or weakness. Blood and laboratory tests reveal no abnormal results. Prognosis is good and children can usually be expected to develop normally.

A minor procedure where a small piece of tissue is removed from the body by a surgeon so that it can be examined under a microscope.

A metabolic muscle disease, associated with failure to thrive, liver and spleen enlargement, and liver failure. It is a genetic disorder, transmitted via an autosomal recessive form of inheritance with onset of symptoms noted in early childhood.

An autosomal recessive disorder of the skeletal muscle, characterized by an inability to relax muscles after repeated contractions, cramps, and stiffness.  Brody disease is also sometimes observed as an autosomal dominant disorder.

Caused by a deficiency of a molecule known as carnitine, that is vital to muscle and heart as part of the normal metabolism of fatty acids. This disorder is one of the metabolic diseases of muscle and is characterized by a number of symptoms including muscle weakness of the proximal muscles of the shoulders and hips, face, palate and neck, and difficulty swallowing. Symptoms usually begin in childhood and are slowly progressive.

A person who has one copy of a particular gene mutation, and one copy that is healthy. In autosomal recessive disorders carriers show no symptoms of the disorder, in most cases, because a person must have two copies of the gene mutation for the disorder to be expressed. In X-linked recessive disorders, females are carriers, because they have an healthy allele on their second X chromosome to "protect" them from symptoms of the disease.

The basic subunit of any living organism. It is the simplest unit that can exist as an independent living system.

One of the congenital myopathies. It is transmitted by an autosomal dominant mode of transmission and is evident at birth or shortly after. The infant usually appears floppy and subsequent milestones are delayed. Infants are often born with a congenital dislocated hip as well. Most patients reach adulthood with a mild handicap that requires no treatment.

See Myotubular Myopathy

Including both autosomal dominant and autosomal recessive neuromuscular disorders characterized by periodic paralysis and myotonia, named for the effect of the gene mutation which controls sodium chloride and calcium channels in the muscle tissue.  These “ion channels” enable the muscle to create an action potential, the force that enables individual muscle cells to move.  The periodic dysfunction of these ion channels means that muscles become temporarily unable to generate movement.

See Hereditary Motor and Sensory Neuropathy

A single “volume” of the DNA library inside each cell.  Human cells contain two sets of 23 chromosomes arranged into pairs (46 chromosomes = 23 pairs), and each of those chromosomes contains thousands of individual instructions for building a person.  When a baby is conceived the mother and the father each donate a single complete set (a total of 23 each) chromosomes which will be used to make up the child.

When an illness or symptom persists for a long period of time.

A disorder caused by inflammation of multiple nerves that causes slowly progressive or repeated episodes of sensation or loss of movement.  This is a less severe form of Guillain-Barré Syndrome.  Symptoms can be treated using plasmapheresis or by using corticosteroids to reduce inflammation.

A trait or disorder that is present at and existing from the time of birth.

One of the congenital myopathies, inherited via an autosomal recessive mode of transmission. Babies affected with this disorder are usually floppy at birth with variable degrees of weakness. The weakness is worse in the first two years of life, after which it either improves or stabilizes.

A group of muscle disorders where affected children are born with varying degrees of muscle weakness.

A form of myasthenia gravis that is caused by an inborn error in the neuromuscular junction, which is the meeting point of the nerve and the muscle it supplies. The structures (nerve terminal, junction between nerve and muscle, or acetylcholine receptors on the muscle fiber surface at the neuromuscular junction) are abnormal in the way they were formed or in the way they work. Affected children are born with the disorder and usually develop symptoms by their first birthday. In some milder forms of the disease, symptoms may become apparent later in adolescence (slow channel syndrome). Most forms are inherited as autosomal recessive disorders, with the exception of the slow channel syndrome which is inherited as an autosomal dominant disorder (and may have been called Familial myasthenia). The congenital myasthenic syndromes are not autoimmune disorders, and thus do not respond to immune suppressive medications. Patients may respond to acetylcholine esterase inhibitors, or other medications, but treatment is individualized depending on what part of the neuromuscular junction is not working properly.

A group of inherited muscle disorders characterized by a specific structural change within the muscle. They often present in a similar way with either a floppy infant syndrome at birth or in infancy or later with muscle weakness. They may have different modes of inheritance.  (See also Fingerprint Body Myopathy, Reducing Body Myopathy, Multicore Myopathy, Central Core Myopathy, Congenital Fibre-type Disproportion, and Sarcotubular Myopathy)

Excessive or abnormal accumulation of secretions in the lungs or airways.

An abnormal shortening of muscle tissue, often caused by muscle weakness.

A group of chemicals (naturally occurring and synthetic) which help to reduce the body’s natural inflammation response.  Some examples include: prednisone, dexamethazone, betamethasone, clobetasol, and hydrocortisone.

Describes any neuromuscular disorder, including muscle weakness in the limbs or respiratory muscles, defects in neuromuscular transmission, or paralysis that results from surgery or trauma.  Largely attributed to infections (see Sepsis).

A bluish discoloration of the skin caused by insufficient levels of oxygen in the blood.

A metabolic muscle disorder inherited by an autosomal recessive mode of transmission. It is associated with liver enlargement and a failure to thrive in the first year of life. Children born with this disorder are floppy at birth with poor head control. Intellect is not affected and life expectancy is considered normal.

A cortisone derivative being investigated for use in children with DMD or BMD. It mimics the positive benefits of prednisone without the same degree of side effects. It is hoped that Deflazacort will slow down the deterioration caused by these disorders and thus will "buy time" for people with muscular dystrophy as researchers work to find an effective treatment.

One of the diseases of the peripheral nerve affecting infants, it is inherited via an autosomal recessive mode of transmission. Symptoms include slow development of motor skills and muscle weakness affecting hands and legs. Rate of progression and severity of symptoms may vary from child to child, but it is usually severe.

A disorder of unknown cause, characterized by inflammatory changes in the skin and muscle. It is thought to be an autoimmune disease, but this is not clear as yet. Can be found at any age, with peaks before puberty and around age 40. Rash, often confined to the face, is followed by weakness in muscles that are often tender and achy. Treatment protocols often utilize steroids such as prednisone.

A nerve disorder caused by diabetes causing numbness or pain in the arms, hands, and feet.  This may also result in damage to internal organs.  Onset is quick and while no cure is available, research has shown intensive management of diabetes may help prevent most neurological damage.

The most important muscle for breathing, located between the chest cavity and the abdominal cavity.

Double vision.

An abbreviation for a chemical called deoxyribonucleic acid. This substance has a very complex molecular structure containing hundreds of thousands of atoms. The way in which these atoms are arranged determines the exact function of each part of the DNA molecule.  Specific sequences of DNA form genes and large groups of genes come together to form chromosomes.

Refers to a characteristic that is expressed when the gene for it is inherited from only one parent.  A dominant gene will block the effects of a single healthy (wild type) gene, so normally only one copy of the mutation is enough to cause the characteristic to appear.Refers to a characteristic that is expressed when the gene for it is inherited from only one parent.  A dominant gene will block the effects of a single healthy (wild type) gene, so normally only one copy of the mutation is enough to cause the characteristic to appear.

A gene that is expressed even when its allele on its paired chromosome is different.

An X-linked recessive disorder of muscle caused by an absence of a protein known as dystrophin. Symptoms are caused by muscle weakness that results in progressive difficulty with walking, mobility and activities of daily living. There is presently no cure or treatment. (See Deflazacort).

Difficulty in speaking because of impairment of the organs of speech or their innervation. It can be caused by weakness of the tongue or facial muscles.

Difficulty in swallowing. Dysphagia can be caused by weakness in the muscles that affect swallowing.

Laboured or difficulty breathing.

A rod shaped protein found in muscle cells that connects to the internal structures of muscle cells and helps them to perform movements.

Neuromuscular disorders (namely Duchenne and Becker Muscular Dystrophy) caused by the lack of sufficient quantities of the protein dystrophin in the muscles.

An EKG is a graphic tracing of the electrical activity of the heart.

Commonly known as an EMG, a test where muscle function is recorded and then studied. The electrical impulses are picked up by electrodes placed on the skin and amplified on a screen in the form of wavelike tracings.

Also known as humeroperoneal muscular dystrophy, this is one of the X-linked recessive disorders. X-linked Emery Dreifuss muscular dystrophy is due to mutations in the gene coding for the protein, emerin. Symptoms usually begin within the first decade of life. Symptoms include wasting and weakness of the shoulder and upper arm muscles, and contractures of the neck, elbows and the Achilles tendon. The muscle weakness is slowly progressive, but cardiac abnormalities may be severe and life-threatening. In addition to the X-linked form of Emery Dreifuss muscular dystrophy, an autosomal dominant form of the disease also exists. This form is due to mutations in the protein, lamin A/C. The symptoms of the autosomal dominant form are the same as the X-linked form.

A protein that speeds up or catalyzes a specific chemical reaction

Refers to the cause of a disease or disorder.

Aggravation of symptoms or increase in the severity of a disease.

An autosomal dominant form of muscular dystrophy, usually appearing late in the first decade of life. Symptoms include weakness of the facial and extra-ocular muscles. Whistling, drinking through a straw and closing the eyelids tightly may be difficult or impossible. Shoulder and upper arm muscles become involved and weakness slowly progresses to include other muscle groups. Progression usually takes place over decades.

One of the congenital myopathies, this is a non-progressive, disorder present from birth, characterized by generalized weakness and hypotonia. It may be associated with delayed motor milestones. Diagnosis is made on a muscle biopsy.

A progressive, autosomal recessive disorder of the nervous system. Onset of symptoms occurs in childhood. Clinical features include progressive ataxia of gait, dysarthria, clumsiness, muscle weakness, scoliosis, and heart problems. Most people lose their ability to walk as the disorder progresses. Diagnosis is confirmed by genetic testing. The disease is caused by an expansion mutation (increased copies of a 3 “letter” code in the DNA) in the gene coding for the protein, “frataxin”.

One of the muscular dystrophies following an autosomal recessive form of transmission. Onset of symptoms always occurs before 9 months of age, and children with this disorder are usually born floppy. Hip and knee contractures are not uncommon by age 3 and few children learn to walk. Sucking reflex may be weak. Children often have severe developmental delays, seizures and difficulty learning to speak. The gene causing this disorder is on chromosome 9 and codes for the protein called “fukutin”. This disorder is very common in Japan.

Genes are found in the nucleus of the cell as tiny segments of DNA in the chromosome. There are approximately 100,000 to 200,000 individual genes located on the 46 chromosomes inside each cell in the human body. Each gene codes for a specific protein.

A form of sugar that the muscles use to store energy for short term use.

Disorders that affect the muscle by disrupting how glycogen is stored and released to supply energy to the muscle cells.  An example of this is Pompe's disease. Infants appear normal for a few weeks after birth but then develop severe hypotonia and enlargement of the heart and liver, as glycogen accumulates in these organs. Pompe’s disease follows an autosomal recessive form of transmission. It is rapidly progressive and life expectancy does not usually exceed 1 year of age.

A characteristic sign seen in any neuromuscular disorder in which the muscles of the hip, upper thigh, and buttocks are weak. It refers to the way that patients stand up from a lying position. They use their arms and hands to "walk up" their legs, and then push their upper bodies to a standing position.

One of the diseases of the peripheral nerve, GBS affects the peripheral nervous system, including the spinal nerves and the cranial nerves. It is believed to be related to an auto-immune mechanism. Early symptoms include may include fever, malaise, and nausea, which relate to an infection that often proceeds the development of Guillain-Barré syndrome Muscular weakness usually begins in the lower limbs and moves upward. Paralysis without loss of sensation is experienced. Many patients experience significant pain in the limbs. The progression of the paralysis eventually plateaus, and recovery begins.. At its maximum point, the paralysis and other symptoms remain unchanged for days or weeks. Improvement begins spontaneously and continues for weeks or occasionally, for months. A full recovery is likely. In severe cases, patients may require assistance with breathing in an intensive care unit. It is important to note that in the early phases the weakness can ascend very rapidly and patients must seek medical attention urgently.

Also known as Charcot-Marie-Tooth (CMT) Disease and peroneal muscular atrophy.  This is a group of hereditary  disorders affecting the peripheral nerves. There are now more than 20 different genetic disorders that fall under this category. Onset of symptoms is typically in the teens to early 20's. More severe forms (Déjérine-Sottas, congenital hypomyelinating neuropathy) present with severe weakness in newborns. In the milder forms (CMT1a being the commonest) weakness and atrophy of the muscles of the feet, lower legs and hands with foot deformities and some loss of sensation are commonly experienced. The degree of disability varies greatly among individuals, even within the same family.

An often under-diagnosed neuropathy which causes periods of weakness, numbness, and paralysis as a result of trivial pressure, stretching or repeated use.  The nerves demyelinate in the area under pressure . This is an autosomal recessive inherited disorder and belongs to Hereditary Motor and Sensory Neuropathy/Charcot Marie Tooth (CMT) family of disorders.

In genetics, when two copies of the same gene (alleles) define different variations of the same characteristic. For example, a gene for black hair, and a gene for red hair.

In genetics, when two copies of the same gene (alleles) define the same variation of a particular characteristic.  For example, both genes may be for brown hair.

See <a href="#EmeryDreifussMD">Emery Dreifuss Muscular Dystrophy</a>

Abnormally decreased muscle tone associated with floppiness. Patients with hypotonia may have muscles that are also weak, but in some situations patients have hypotonia with normal muscle strength.

See Antibodies

One of the inflammatory myopathies, with onset most frequently after the age of 50. It is more common in males. Slowly progressive muscle weakness occurs in the extremities and hip girdle region. Diagnosis must be made by muscle biopsy.

Also known as Pompe's disease and Type I glycogenosis. Infants appear normal for a few weeks after birth but then develop severe hypotonia and enlargement of the heart and liver, as glycogen accumulates in these organs. It follows an autosomal recessive form of transmission. It is rapidly progressive and life expectancy does not usually exceed 1 year of age.

Also known as neuromyotonia, it can appear at any age and in either sex. Individuals experience brief contractions of muscles, known as myokymia which can range in severity from very mild to quite severe. Associated symptoms are insomnia, difficulty walking, and stiffness of the wrists. The body may become stooped. An effective treatment, in the form of diazepam or Clonazepam is used to relieve the continuous contractions. It is felt to be a disorder of the ion channels in muscle.

The place of union or coming together of two parts.

A late-onset X-linked recessive disorder affecting mostly men in their third to fifth decade of life.  The disorder is slowly progressive, and causes weakness in the extremities and muscles used for speech and swallowing.  Formally known as spinal and bulbar muscular atrophy, or SBMA. There is no known cure.

This disorder and its symptoms are quite different from myasthenia gravis, despite the similarity in name. It is found more frequently in men than in women and usually occurs after the age of 40. Symptoms include weakness and tiredness around the hips and subsequent difficulty rising from a chair. It progresses to involve legs, shoulders and arms. Backache that improves as the day progresses and fatigue are also common symptoms. Exercise works to improve symptoms. Certain medications (3,4 diaminopyridine) may also be of benefit. A correct diagnosis requires a careful EMG study by an expert familiar with the disease. The disease may be associated with some forms of cancer, particularly lung cancer. In these patients, it is thought that antibodies directed against the tumor also act against the nerve-muscle junction.

There are now numerous autosomal dominant and autosomal recessive forms of limb-girdle muscular dystrophy (LGMD). Symptoms of. shoulder and hip girdle muscle weakness appear either in childhood or early adulthood. There is a great deal of variability in the severity of the disease.. In some cases, respiratory muscles can become involved. Progressive nature of the disorder may result in loss of ambulation or respiratory failure.

In genetics, refers to the specific area on a chromosome where a gene is located.

A syndrome affecting individuals undergoing general anesthesia, marked by rapid rise in body temperature, signs of increased muscle metabolism and usually, rigidity. The sensitivity is inherited as an autosomal dominant trait, due to genetic mutations in the ryanodine receptor in muscle. Mutations in this same gene can cause central core myopathy, and these patients are also at risk for malignant hyperthermia (MH). It is absolutely critical that patients with a family history of malignant hyperthermia or central core disease, wear a Medic Alert bracelet. The bracelet should state that they have a risk of MH, and that they must avoid “inhalational anesthetics and depolarizing neuromuscular blocking agents”. A similar, but not identical reaction to anesthetics can be seen in patients with Duchenne/Becker muscular dystrophy, in patients with myotonic muscular dystrophy, and in some forms of limb-girdle muscular dystrophy. All patients with neuromuscular disease should discuss this issue with the anesthetist prior to any form of surgery. Avoidance of the potentially harmful anesthetics is easily achieved if the anesthetist is aware of the risks in advance.

See Myophosphorylase Deficiency

Relating to all the chemical reactions that take place inside of a cell of a living organism to produce the energy needed by that cell to perform its functions.

One of the congenital myopathies, this disorder presents with hypotonia, general muscle wasting, mild facial weakness and delay in motor milestones. It is often associated with scoliosis. Diagnosis requires a muscle biopsy.

The small organelles that exist inside each cell. Mitochondria are the energy packets of the cell. They  convert fatty acids and carbohydrates from the food we eat into energy.

Disease processes characterized by dysfunction of mitochondria in skeletal muscle. Because of this process, less and less energy is generated within the cell, leading to muscle weakness. Mitochondria are present in every cell of the body, and thus in many types of mitochondrial disease, patients have symptoms in many tissues in addition to muscle, such as the heart, brain (seizures, cognitive impairment), liver, eye (night blindness), ear (deafness), and pancreas (diabetes). The life expectancy of the person can be compromised, and in severe cases death occurs in infancy. Inheritance of mitochondrial disease is very complex. Mitochondria have their own small set of genes, and also use genes found in the nucleus of the cell. Thus, genetic mutations can occur in the mitochondrial genes or in the nuclear genes. Nuclear gene mutations follow the rules of autosomal recessive or dominant inheritance, and most patients with this type of mitochondrial genetic disorder have autosomal recessive inheritance (i.e.: both parents carry the mutation on one copy of the mitochondrial gene in question, but appear normal due to compensation by the healthy copy of the same gene. A child who inherits two copies of this mitochondrial gene mutation has no healthy copy, and thus the mitochondria lack an important gene required for function). Mutations in mitochondrial genes are even more complex. All the mitochondrial are passed from the mother (in the egg) and none are contributed by the sperm (unlike the situation of nuclear genes where each parent contributes equally). Thus, in the case of mitochondrial gene mutations, inheritance follows in the maternal side of the family only. Occasionally the genetic mutation occurs for the first time in the developing baby. In this situation there are no other affected family members.

Amyotrophic Lateral Sclerosis (ALS)

The motor unit is defined as including the anterior horn cell, the nerve axon emanating from it (which forms part of a peripheral motor nerve), the nerve-muscle junction, and the muscle supplied by this nerve-muscle junction. Most neuromuscular disorders affect some specific part of this system.

One of the congenital myopathies, this disorder presents with early onset of limb and trunk weakness with delayed or failure to attain motor milestones. A muscle biopsy is required for diagnosis.

Contractile tissue found in animals and humans used to produce movement.

A general term that refers to a group of chronic muscle disorders characterized by progressive weakness and wasting of the voluntary muscles that control body movement.

A change in the DNA sequence, loss of part of the DNA sequence, or an insertion of extra DNA sequence into a specific gene.

An acquired (non-genetic) neuromuscular disease that affects the strength and stamina of voluntary muscles. It is caused by an attack by the immune system on the neuromuscular junction.. Current treatment modalities may include thymectomy, plasmapheresis or intravenous immune globulin, immune suppressant medications and anticholinesterase drugs (which allow the chemical acetylcholine to remain at the neuromuscular junction longer, thus improving nerve to muscle communication). Remission occurs in some patients, while some patients require therapy for life. (See also Congenital Myasthenic Syndromes)

The insulating layer surrounding peripheral nerves. Myelin is also found in the brain.

One of a group of metabolic diseases of muscle in which a known biochemical defect (in this case, deficiency of an enzyme known as adenylate deaminase) is associated with symptoms of exercise intolerance. The cardinal symptoms are usually fatigue and muscle pain.

Any disease of voluntary muscle.

Also known as McArdle's disease, this disorder occurs when there is a deficit in the enzyme myophosphorylase and a person is unable to utilize glycogen as a source of energy. A person with this disorder will experience difficulty and cramping pain with heavy lifting or exercise. It is usually inherited via autosomal recessive inheritance. Onset is usually before age 10.

A rare disorder characterized by deposition of bone in subcutaneous tissue and along muscle. It usually appears in the first or second year of life and is progressive. The extent of disability is variable depending on the extent of ossification. It is thought to be genetic in origin. Treatment is symptomatic.

Inability to relax a muscle following contraction. It is often noted in the handgrip, or by trouble opening the eyes after forceful eye closure. It is a common symptom of myotonia congenital, as well as in myotonic dystrophy.

There are two main forms of myotonia congenital. Thomsen's disease, I is an autosomal dominant form, while Becker myotonia (no relationship to Becker muscular dystrophy) is inherited in an autosomal recessive manner.  The major symptom is myotonia, which is often quite severe and widespread and can result in a functional disability. An affected person may have difficulty relaxing the grip, opening the eyes, running and swallowing. It is a painless disorder and breathing is not affected. Some patients are treated successfully with Mexilitine, but this must be under supervision by a doctor.

Also known as Steinert's disease, this is the most commonly occurring form of muscular dystrophy. It follows an autosomal dominant form of inheritance and can affect children or adults of either sex. The adult form becomes apparent between 10 and 30 years of age, though symptoms can be so mild that a person may not realize he/she is affected. Symptoms of the adult form vary greatly between individuals. Muscle weakness begins gradually and progresses slowly. A person will notice facial weakness. Stiffness (myotonia) is a troubling symptom for some patients.. Other organs of the body are frequently affected, including the eyes (cataracts), heart (palpitations, abnormal heart rhythms which can be life-threatening), smooth muscle of the digestive tract (choking, difficulty swallowing), the endocrine system (hypothyroidism, glucose intolerance), and the lungs (poor breathing at night) A congenital form of myotonic dystrophy can occur in children born to mothers who have the disorder themselves. Babies are profoundly weak and hypotonic at birth. They experience symptoms, which can range from difficulties in swallowing, breathing and sucking to life-threatening problems. Following the newborn period, children often encounter developmental delays in the areas of speech and motor development. Children affected by this disorder usually show improved muscle strength over the first few years, and may walk independently.

Also known as centronuclear myopathy, this disorder is characterized by hypotonia, feeding difficulties and delay of motor milestones. Facial weakness, ptosis and opthalmoplegia (limited eye movements) may be present. Different forms may be autosomal dominant or autosomal recessive. Another form, X-linked myotubular myopathy, is the most severe and is often fatal. Babies have respiratory difficulties and swallowing problems from birth and often require ventilator support.

Also known as rod body myopathy, this disorder is characterized by diffuse muscle weakness and hypotonia, facial weakness, and  a high arched palate It  may be  present at birth or appears in infancy, but some forms of this condition appear in adulthood (usually with symptoms of cardiac dysfunction). The severity of the symptoms ranges from benign and non-progressive in some cases, to severe, progressive and fatal in others. There are now several different genes associated with this disorder.

Anything that pertains to the nerves, muscles, or the nerve-muscle junction.

The point at which a nerve and a muscle meet.  This is where the signal that is being carried along a nerve is passed to a muscle cell. The signal is then translated into  electrical activity leading to a muscle contraction.

See Isaac Syndrome

A nerve cell. Neurons function in initiation and conduction of impulses.

A disorder, either genetic or acquired (autoimmune or traumatic) that leads to impaired function of one or more peripheral nerves.

The central part of most living cells. It is the structure in the cell containing the genetic material. It contains the chromosomes and controls all the activities of the cell.

The central part of most living cells. It is the structure in the cell containing the genetic material. It contains the chromosomes and controls all the activities of the cell.

An autosomal dominant form of muscular dystrophy that is characterized mainly by ptosis (drooping of the eyelids) and dysphagia (trouble swallowing). It usually occurs later in life (40 to 70 years). Progression is slow, but weakness of throat muscles may become a serious problem. In addition, most people have some degree of facial weakness and may experience weakness and atrophy in the muscles of the hips and shoulders. In Canada, it is most common in people from Quebec.

A neuromuscular disorder  characterized only by myotonia, without any attacks of paralysis. The myotonia is worse after repeated use or exercise and is exacerbated by cold. Genetic transmission is autosomal dominant and onset of symptoms usually occurs in adulthood.

Includes the hypokalemic and hyperkalemic types. Patients with these rare disorders develop  anytime from infancy to the 30's. They are characterized by bouts of limb and neck weakness and paralysis which range from severe episodes. Episodes can occur frequently or may be weeks or months apart.. They are both genetic disorders, transmitted via an autosomal dominant transmission.

Any nerve in the body that leads from the spinal cord to the muscles of the body (motor nerve), or  nerves that bring sensory information from the body back to the spinal cord (sensory nerves).

Also known as Andermann syndrome, this is an autosomal recessive disorder, occurring in young children. It is a severe disorder characterized by an absence of deep tendon reflexes, hypotonia, developmental delay, facial asymmetry, high arched palate, ptosis, scoliosis and seizures. Life expectancy is shortened. Images of the brain reveal absence of the main communication pathway (the corpus callosum), a pathway that is involved in the passage of information between the right and left sides of the brain.

See Hereditary Motor and Sensory Neuropathy

Metabolic disorder of muscle resulting from absence of the enzyme PFK. Symptoms include fatigue and achy pain in the muscles that increases with additional exertion. Attacks may be accompanied by nausea and vomiting. Occurs typically in childhood, with wide variation in severity and progression.

The physical and therapeutic techniques commonly used to maintain strength and maximize range of motion, posture and comfort.

Removal of a portion of blood, separation of the blood cells by centrifugation so as to remove the plasma portion containing antibodies and replacement with plasma or sterilized albumin separated from donor blood. It is often part of the treatment protocol in myasthenia gravis, Guillain-Barré syndrome, and severe dermatomyositis.

A viral infection that primarily infects the anterior horn cells in the spinal cord. Also called: poliomyelitis and infantile paralysis. The disease can lead to paralysis of one or more limbs, and can be life threatening. Natural infection is now rare in Canada due to the routine immunization of infants.

An inflammatory disorder of skeletal muscle. Symptoms include difficulty climbing stairs or rising from low seats, lifting packages, or working with arms outstretched or over the head. It is treated with steroids and immunosuppressive drugs. Treatment success is variable. The disorder does not resolve on its own.

See Infantile Acid Maltase Deficiency

A molecule composed of amino acids that carries out the work of the cell. The proteins manufactured by the genes are responsible for all structures and functions of living cells from eye colour to muscle function.

A common characteristic in Duchenne muscular dystrophy where the calf muscles are prominent. This prominence is due to increased fat deposits rather than muscle tissue.

Abnormal downward displacement of a body part. Especially refers to drooping of upper eyelid. A common feature of myasthenia gravis, congenital myasthenic syndromes, oculopharyngeal muscular dystrophy, and some congenital myopathies.

Refers to a characteristic that is expressed only when both copies of the gene coding for the characteristic (i.e.: protein) are mutated.

One of the congenital myopathies. Hypotonia occurs early and motor milestones are either late or not attained. Profound weakness is progressive and involves both distal and proximal muscles.

Lessening in severity or abatement of symptoms. Periods of remission are common in myasthenia gravis.

An autosomal dominant neuromuscular disorder, characterized by muscle cramps, pain and stiffness in the legs, arms and neck which increases with exercise and cold temperatures.  This disorder is named for the visible and sometimes painful, wave-like movement of the muscles after they are stretched.  Symptoms occur early in the first or second decades of life.

See Nemaline Myopathy

One of the congenital myopathies, this is a non-progressive form of muscle disease. There may be a slight delay of motor milestones. Walking or running may be clumsy. Intellect is not affected.

Also known as chondrodystrophic myotonia, this syndrome affects children at birth who present with a variety of signs and symptoms including short stature with a short neck, flexion contractures, kyphosis (convex curve of the spine) and facial characteristics such as low set ears, 2 rows of eye lashes, narrow palpebral fissures, pinched nose and abnormalities of the teeth. Intellect is often impaired. The gene for this disorder has been recently discovered, and codes for a protein called perlecan.

Sideways deviation in the normally straight line of the spine. In the case of neuromuscular disorders, it results from muscular weakness or localized muscle imbalance. The curvature may be flexible at first, with little rotation, but as the scoliosis progresses the curvature becomes more pronounced and fixed. It can be treated with varying degrees of success, with surgery.

Originally defined as a decomposition of organic matter and tissue by bacteria or fungi.  Medically, has come to describe the severe systemic response to an infection.

The 23rd chromosomal pair, where the sex of the unborn child is determined. Each female carries two X chromosomes and each male carries one X and one Y chromosome. At conception, a child receives an X chromosome from mom and either an X chromosome (resulting in a female child) or a Y chromosome (resulting in a male child) from dad.

Refers to the muscles used in movement or posture. Does not include muscles of the digestive tract, or the heart muscle.

A surgical procedure done to correct scoliosis. In this procedure, the vertebrae in the spine are surgically joined.

An autosomal recessive disorder of muscle weakness and wasting caused when the motor nerves that stimulate and control muscles fail to function. As a result, the muscles atrophy. There are a variety of presentations of the disorder. Severity of symptoms can range from life threatening in Type I SMA, to mild weakness in the adult form. At present, there is no treatment or cure. The gene for SMA is on chromosome 5, and is due to a mutation in the survival motor neuron gene. All of the autosomal recessive forms of SMA are due to mutations in the survival motor neuron gene, but the severity of the disease is influenced by the function of a related gene (survival motor neuron gene 2). The better the function of the survival motor neuron 2 gene, the milder the clinical features.

An autosomal recessive disorder with symptoms appearing in the first few months of life. It is slowly progressive, affecting nerve cells. Frequent falls and loss of balance are noted early. A mobility aid is usually required between the ages of 25 and 40. It has no effect on either intelligence or life expectancy.

An autosomal dominant group of degenerative disorders with symptoms that include one or more of: gait ataxia, dysarthria, spasticity, dystonia, dementia, loss of vision and hearing, and peripheral neuropathy. Onset of symptoms is usually between the ages of 20 and 40 years. Most people will eventually lose their ability to walk. Life expectancy is shortened. Genetic testing for several of these disorders is now available.

(See Myotonic Dystrophy)

A term applied to a large group of substances chemically related to sterols. Steroid hormones are normally produced in small amounts by cells in the adrenal cortex. Several steroid medications exist, such as prednisone and Deflazacort.

A treatment in myasthenia gravis where the thymus gland is surgically removed.

Located under the breastbone, this gland is involved in the production of antibodies. It is believed to play a central role in the development of myasthenia gravis.

A surgical opening in the trachea or windpipe through which a tube is inserted to assist with respiration.

Muscles whose movements are under voluntary control.

In genetics, refers to the healthy, un-mutated copy of an allele.  This “normal” gene is the one that does not cause a disorder, and also is found most often in a population.

The gene mutation is carried on the X (sex) chromosomes. An X-linked disorder is passed on to male children by their mothers, who carry the gene mutation on one of their X chromosomes. When his mother is a carrier, a male child has a 50% chance of inheriting the gene mutation and a 50% chance of being unaffected. A female child has a 50% chance of being a carrier and a 50% chance of being unaffected.