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Myotonic dystrophy

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Last Updated: 02 July 2021

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Myotonic dystrophy

Other namesDystrophia myotonica, myotonia atrophica, myotonia dystrophica
SpecialtyMedical genetics , pediatrics , physical medicine and rehabilitation
SymptomsMuscle loss , weakness, muscles which contract and are unable to relax
ComplicationsCataracts , intellectual disability , heart conduction problems
Usual onset20s to 30s
DurationLong term
TypesType 1, type 2
CausesGenetic disorder ( autosomal-dominant )
Diagnostic methodGenetic testing .
TreatmentBraces, wheelchair, pacemakers , non invasive positive pressure ventilation
MedicationMexiletine , carbamazepine , tricyclic antidepressants , nonsteroidal anti inflammatory drugs
Frequency>1 in 8,000 people

Myotonic Dystrophy is an inherited type of Muscular Dystrophy that affects muscles and other body systems. People who have Myotonic Dystrophy have muscle wasting and weakness in their lower legs, hands, neck and face that get worse over time. Signs and symptoms of Myotonic Dystrophy usually develop when a person is in his or her twenties or thirties. Severity of Myotonic Dystrophy varies widely among those who have it, even among family members. Weakness and muscle wasting that occur slowly progress to the point of disability. Usually, disability does not become severe until fifteen to twenty years after symptoms appear. Progression of muscle weakness is slower and is less serious in people who are older when muscle weakness is first notice. There are two types of Myotonic Dystrophy: Type 1 and Type 2. Two types are caused by alterations in two different genes. Symptoms of Type 2 Myotonic Dystrophy are usually milder than those of Type 1. Severe Type of Type 1 Myotonic Dystrophy can be seen at birth. This form of Type 1 is called congenital Myotonic Dystrophy. Congenital Myotonic Dystrophy has only been seen in Type 1 Myotonic Dystrophy and not in Type 2. Myotonic Dystrophy is the most common form of Muscular Dystrophy that begins in adulthood. It affects about 1 in 8 000 people worldwide. Type 1 Myotonic Dystrophy is the most common form in most countries. The commonness of the two types depends upon the person's ethnic background. For example, Type 2 Myotonic Dystrophy is as common as Type 1 in people who have German ancestry. Myotonic Dystrophy is an inherited type of Muscular Dystrophy that affects muscles and other body systems. People who have Myotonic Dystrophy have muscle wasting and weakness in their lower legs, hands, neck and face that get worse over time. Signs and symptoms of Myotonic Dystrophy usually develop when a person is in his or her twenties or thirties. The severity of Myotonic Dystrophy varies widely among those who have it, even among family members. Weakness and muscle wasting that occur slowly progress to the point of disability. Usually, disability does not become severe until fifteen to twenty years after symptoms appear. Progression of muscle weakness is slower and is less serious in people who are older when muscle weakness is first notice. There are two types of Myotonic Dystrophy: Type 1 and Type 2. Two types are caused by alterations in two different genes. Symptoms of Type 2 Myotonic Dystrophy are usually milder than those of Type 1. Severe Type of Type 1 Myotonic Dystrophy can be seen at birth. This form of Type 1 is called congenital Myotonic Dystrophy. Congenital Myotonic Dystrophy has only been seen in Type 1 Myotonic Dystrophy and not in Type 2. Myotonic Dystrophy is the most common form of Muscular Dystrophy that begins in adulthood. It affects about 1 in 8 000 people worldwide. Type 1 Myotonic Dystrophy is the most common form in most countries.

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Related video

21 September 2020Myotonic dystrophy- causes, symptoms, diagnosis, treatment, pathology

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Signs and symptoms

Presentation of symptoms and signs varies considerably by form, severity and even unusual DM2 phenotypes. Dm1 symptoms for DM2 include problems with executive function and hypersomnia. Conduction abnormalities are more common in DM1 than in DM2, but all people are advised to have an annual ECG. Both types are also associated with insulin resistance. Myotonic DYSTROPHY may have cortical cataract with blue dot appearance, or posterior subcapsular cataract. Dm2 is generally milder than DM1, with generally fewer DM2 people requiring assistive devices than DM1 people. In addition, severe CONGENITAL form that affects babies in DM1 has not been found in DM2 and early ONSET of symptoms is rarely noted to appear in younger people in medical literature. Symptoms may appear at any time from infancy to adulthood. Dm causes general weakness, usually beginning in muscles of hands, feet, neck, or face. It slowly progresses to involve other muscle groups, including the heart. Dm affects a wide variety of other organ systems as well.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Genetics

Myotonic Dystrophy is a genetic condition which is inherited in Autosomal dominant pattern and thus will be passed along to 50% of carrier's offspring, on average. Myotonic Dystrophy is one of several well known trinucleotide repeat disorders. Certain areas of DNA have repeat sequences of three or four nucleotides. Myotonic Dystrophy is an inherited disease. A severe form of DM, congenital Myotonic Dystrophy, may appear in newborns of mothers who have DM. Congenital Myotonic Dystrophy can also be inherited via paternal gene, although it is said to be relatively rare. Congenital means that condition is present from birth.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Diagnosis

Myotonic dystrophy subtypes

TypeGeneRepeatAnticipationSeverity
DM1DMPKCTGYesModerate-severe
DM2ZNF9CCTGMinimal/noneMild-moderate

Diagnosis of DM1 and DM2 can be difficult due to the large number of neuromuscular disorders, most of which are very rare. More than 40 neuromuscular disorders exist with close to 100 variants. As a result, people with multiple symptoms that may be explained by complex disorder such as DM1 or DM2 will generally be referred by their primary care physician to a neurologist for diagnosis. Depending on presentation of symptoms, people may be referred to a number of medical specialists, including cardiologists, ophthalmologists, endocrinologists, and rheumatologists. In addition, clinical presentation is obscured by the degree of severity or presence of unusual phenotypes. Clinical presentations for both people with DM1 and DM2 commonly differ from the conception of diseases held by many neurologists. Clinicians who are less familiar with myotonic dystrophies may expect people with both forms to present with more severe, classic symptoms of DM1. As a result, people may remain undiagnosed or be misdiagnosed. Useful clinical clue for diagnosis is failure of spontaneous release of hands following strong handshakes due to myotonia which accompanies muscle weakness. Though there is presently no cure for DM and management is currently symptom base, precise diagnosis is still necessary to anticipate multiple other problems that may develop over time. Accurate diagnosis is important to assist with appropriate medical monitoring and management of symptoms. In addition, Genetic Counseling should be made available to all people because of the high risk of transmission. Potentially serious anesthetic risks are important to note, so the presence of this disorder should be brought to the attention of all medical providers.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Management

There is currently no cure for or treatment specific to myotonic Dystrophy. Therefore, focus is on managing complications of disease, particularly those relating to the cardiopulmonary system as these account for 70% of deaths due to DM1. Pacemaker insertion may be required for individuals with Cardiac conduction abnormalities. Improving quality of life, which can be measured using specific questionnaires, is also main objective of medical care. Central sleep apnea or obstructive sleep apnea may cause excessive daytime sleepiness, and these individuals should undergo sleep study. Non - invasive ventilation may be offered if there is an abnormality. Otherwise, there is evidence for use of modafinil as a central nervous system stimulant, although the Cochrane review has described evidence thus far as inconclusive. Some small studies have suggested that imipramine, clomipramine and taurine may be useful in treatment of myotonia. However, due to weak evidence and potential side effects such as Cardiac arrhythmias, these treatments are rarely used. A recent study in December 2015 showed that the common FDA approved antibiotic, Erythromycin, reduced myotonia in mice. Human studies are planned for Erythromycin. Erythromycin has been used successfully in patients with gastric issues. Alter splicing of muscle - specific chloride channel 1 has been shown to cause myotonic phenotype of DM1 and is reversible in mouse models using Morpholino antisense to modify splicing of ClC - 1 mRNA.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Epidemiology

Dm1 is the most prevalent form of condition and is generally the most severe. This form affects at least 1 in 2 300 people worldwide or 140 000 people in the United States alone, although prevalence may be significantly under - report. Dm1 can occur from birth to old age, and is divided into further subtypes based on the age of the affected individual when symptoms first appear. Symptoms vary greatly between patients, from minor muscle pain to serious respiratory and cardiac issues. The congenital form of DM1 is the most severe version and has distinct symptoms that can be life - threatening. Below are explanations of three DM1 subtypes that vary based on age at onset: congenital: Presents potentially life - threatening issues at birth. Congenital DM1 is the most severe and earliest occurring form of myotonic dystrophy. It occurs when a mother, who often is not aware she has DM1, passes mutation that causes DM1 onto her child. During pregnancy, she may have noticed less than normal levels of fetal activity, had condition called hydramnios where excess amniotic fluid accumulates, or had long, difficult labor. Childhood Onset: Typically first presented with intellectual disability, and learning disabilities. After relatively normal birth and infancy, individuals with childhood - Onset DM1 develop symptoms sometime between early childhood and early adolescence. The time of onset is often dependent on the astuteness of the observer, and is typically first presented with intellectual disability, and learning disabilities. Adult Onset: characterized by distal muscle weakness, atrophy, myotonia and many other multisystemic issues. With adult - Onset DM1, symptoms can appear from late adolescence through old age, and usually worsen over time. Depending on the severity of symptoms, patients with adult DM1 may be categorized as having either a mild or classical form of disease. Individuals with mild form of adult - Onset DM1 are often not aware they have a disorder. Muscle symptoms may be attributed to general stiffness or arthritis. Non - muscle symptoms tend to be moderate and are often diagnosed and treated as independent issues. These individuals are unlikely to be diagnosed as having myotonic dystrophy unless a family member is identified with a more severe form of disease and testing is initiate.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Myotonic Dystrophy (DM)

Myotonic Dystrophy is the most common late - developing form of Muscular Dystrophy. There are two types of Myotonic Dystrophy, type 1 and type 2, both of which are caused by genetic mutations and are inherited in autosomal dominant manner. Patients with either typeA of DM typically experience gradually worsening muscle weakness, muscle wasting, and difficulties in relaxing muscles. Other parts of the body, including eyes, heart, and endocrine system are also affected in DM. Dm2 is rare than DM1 and generally runs a milder course. Although both types of DM share similar symptoms, they are caused by different disease processes.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Symptomatic treatments:

Table I.

Disease subtypeClinical findingsRepeat sizeAge of onset
Normal (premutation)Noneup to 49N/A
MildMild myotonia, cataracts50-15020-70 years
ClassicWeakness, cataracts, myotonia, cardiac rhythm disturbances100-100010-30 years
Congenitalprenatal onset severe hypotonia, respiratory failure, neurocognitive impairment in survivors>2000birth

Treatment of Myotonic Dystrophy involves a multidisciplinary team. A neurologist oversees various needs of patients and directs care. Neurologists may recommend that myotonia, inability to relax muscles, be treated with drug such as mexiletine. Ecg, and often echocardiogram,s will be performed to assess the heart's rhythm and function. Test of lung function will also be perform. Depending on the neurologist's findings and results of these tests, consultation with other specialists who also have expertise in Myotonic Dystrophy - such as cardiologists, pulmonologists, and ophthalmologists - will be recommended for additional treatment. Specialists in rehabilitation medicine are present in clinic to meet with patients and provide individualized exercise and stretching programs for treatment of weakness and contractures. On the same day, patients will be evaluated for need for splints and orthotics to help with hand or foot function. Myotonic Dystrophy is a complex disorder that affects many organ systems throughout the body. Most people with Myotonic Dystrophy can lead full, successful lives. This requires involvement of health care professionals with experience and dedication to disease as are found at Kennedy Krieger.

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Table II.

Organ systemManifestations
Gastrointestinaldysphagia, gastroparesis, constipation
Ocularcataracts, ptosis
Endocrinehypogonadism (males), hyperinsulinism
CNSexcessive sleepiness, sleep apnea
Skinpremature balding (males)
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Myotonic dystrophy type 1

Table I.

Disease subtypeClinical findingsRepeat sizeAge of onset
Normal (premutation)Noneup to 49N/A
MildMild myotonia, cataracts50-15020-70 years
ClassicWeakness, cataracts, myotonia, cardiac rhythm disturbances100-100010-30 years
Congenitalprenatal onset severe hypotonia, respiratory failure, neurocognitive impairment in survivors>2000birth

Dm2 was previously termed proximal Myotonic myopathy and shares many of the features of DM1. 65 - 68 DM2 is an autosomal dominant disorder caused by mutation in ZNF9 Gene on chromosome 3q21. Znf9, gene encoding zinc finger protein 9, is the only gene known to be associated with DM2. The first intron in ZNF9 contains complex repeat motif nnn. Expansion of CCTG repeat causes DM2. The 69 70 repeat expansion for DM2 is much larger than for DM1, ranging from 75 to over 11000 repeats. Unlike DM1, size of repeat DNA expansion does not correlate with age of onset or disease severity in DM2. Anticipation is less evident clinically in DM2. The Congenital form of DM2 has not been report.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

Table II.

Organ systemManifestations
Gastrointestinaldysphagia, gastroparesis, constipation
Ocularcataracts, ptosis
Endocrinehypogonadism (males), hyperinsulinism
CNSexcessive sleepiness, sleep apnea
Skinpremature balding (males)
* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Other myotonic disorders

Table I.

Disease subtypeClinical findingsRepeat sizeAge of onset
Normal (premutation)Noneup to 49N/A
MildMild myotonia, cataracts50-15020-70 years
ClassicWeakness, cataracts, myotonia, cardiac rhythm disturbances100-100010-30 years
Congenitalprenatal onset severe hypotonia, respiratory failure, neurocognitive impairment in survivors>2000birth

Myotonic Dystrophy is part of a group of inherited disorders called muscular dystrophies. It is the most common form of muscular dystrophy that begins in adulthood. Myotonic Dystrophy is characterized by progressive muscle wasting and weakness. People with this disorder often have prolonged muscle contractions and are not able to relax certain muscles after use. For example, person may have difficulty releasing their grip on doorknob or handle. Also, affected people may have slur speech or temporary locking of their jaw. Other signs and symptoms of Myotonic Dystrophy include clouding of the lens of eye and abnormalities of electrical signals that control heartbeat. Some affected individuals develop a condition called diabetes mellitus, in which blood sugar levels can become dangerously high. Features of Myotonic Dystrophy often develop during a person's twenties or thirties, although they can occur at any age. The severity of condition varies widely among affected people, even among members of the same family. There are two major types of Myotonic Dystrophy: Type 1 and Type 2. Their signs and symptoms overlap, although Type 2 tends to be milder than Type 1. Muscle weakness associated with Type 1 particularly affects muscles farthest from the center of the body, such as those of lower legs, hands, neck, and face. Muscle weakness in Type 2 primarily involves muscles close to the center of the body, such as those of the neck, shoulders, elbows, and hips. Two types of Myotonic Dystrophy are caused by mutations in different genes. There are two variations of Myotonic Dystrophy Type 1: Mild and congenital types. Mild Myotonic Dystrophy is apparent in mid to late adulthood. Affected individuals typically have Mild Myotonia and Cataracts. Congenital Myotonic Dystrophy is often apparent at birth. Characteristic features include weak muscle tone, inward - and upward - turning foot, breathing problems, delayed development, and intellectual disability. Some of these health problems can be life - threatening. Both types of Myotonic Dystrophy are inherited in autosomal dominant pattern, which means one copy of altered gene in each cell is sufficient to cause disorder. In most cases, affected person has one parent with condition. As Myotonic Dystrophy is passed from one generation to the next, disorder generally begins earlier in life and signs and symptoms become more severe. This phenomenon is called anticipation. Evidence for anticipation appears only in Myotonic Dystrophy Type 1. In this form of disorder, anticipation is caused by an increase in length of unstable region in DMPK gene. Longer unstable regions in CNBP gene do not appear to influence age of onset of Myotonic Dystrophy Type 2.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

Table II.

Organ systemManifestations
Gastrointestinaldysphagia, gastroparesis, constipation
Ocularcataracts, ptosis
Endocrinehypogonadism (males), hyperinsulinism
CNSexcessive sleepiness, sleep apnea
Skinpremature balding (males)
* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Clinical description

Table I.

Disease subtypeClinical findingsRepeat sizeAge of onset
Normal (premutation)Noneup to 49N/A
MildMild myotonia, cataracts50-15020-70 years
ClassicWeakness, cataracts, myotonia, cardiac rhythm disturbances100-100010-30 years
Congenitalprenatal onset severe hypotonia, respiratory failure, neurocognitive impairment in survivors>2000birth

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

Table II.

Organ systemManifestations
Gastrointestinaldysphagia, gastroparesis, constipation
Ocularcataracts, ptosis
Endocrinehypogonadism (males), hyperinsulinism
CNSexcessive sleepiness, sleep apnea
Skinpremature balding (males)
* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Causes

Table I.

Disease subtypeClinical findingsRepeat sizeAge of onset
Normal (premutation)Noneup to 49N/A
MildMild myotonia, cataracts50-15020-70 years
ClassicWeakness, cataracts, myotonia, cardiac rhythm disturbances100-100010-30 years
Congenitalprenatal onset severe hypotonia, respiratory failure, neurocognitive impairment in survivors>2000birth

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

Table II.

Organ systemManifestations
Gastrointestinaldysphagia, gastroparesis, constipation
Ocularcataracts, ptosis
Endocrinehypogonadism (males), hyperinsulinism
CNSexcessive sleepiness, sleep apnea
Skinpremature balding (males)
* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Sources

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

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