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Disease Profile

Myotonic dystrophy type 1

Prevalence
Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.
1-5 / 10 000

33,100 - 165,500

US Estimated

1-5 / 10 000

51,350 - 256,750

Europe Estimated

Age of onset

Antenatal

ICD-10

G71.1

Inheritance

Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease

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Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype

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X-linked
dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.

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X-linked
recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder

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Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.

Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.

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Not applicable

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Other names (AKA)

Dystrophia myotonica type 1; DM1; Steinert disease;

Categories

Congenital and Genetic Diseases; Endocrine Diseases; Eye diseases;

Summary

Myotonic dystrophy type 1 (MD1), one of the two types of myotonic dystrophy, is an inherited type of muscular dystrophy that affects the muscles and other body systems (e.g., heart, eyes, endocrine system, and central nervous system).[1] MD1 has three forms that somewhat overlap: the mild form, classic form, and congenital form (present at birth). The mild form has the least severe symptoms of the different forms of MD1 and is associated with a normal life span. The classic form is characterized by muscle weakness and wasting, prolonged muscle tensing (myotonia), cataract, and often, abnormal heart function. Adults with the classic form may become physically disabled and may have a shortened life span. The congenital form is characterized by severe generalized weakness at birth (hypotonia), often causing complications with breathing and early death. MD1 is inherited in an autosomal dominant manner and is caused by mutations in the DMPK gene. Treatment is based on the signs and symptoms present.[2]

Symptoms

People with MD1 have progressive muscle wasting and weakness beginning in their 20's or 30's. The muscle wasting and weakness develop in their lower legs, hands, neck and face. They also have stiffness and tightness of their muscles (called myotonia), so they are slow to relax certain muscles after using them. This condition is characterized by difficulty releasing the hand from a handshake or a doorknob. In addition to muscle weakness and wasting, people who have MD1 may have fatigue, muscle pain, difficulty swallowing, clouding of the lens in their eyes (cataracts), and irregularities in the electrical control of their heartbeat (cardiac conduction defects). People with advanced disease may develop respiratory complications. Men with MD1 have changes in their hormones that can cause balding and sometimes the inability to father a child (infertility).[1][2] The severity of symptoms varies among people with MD1.

Compared to myotonic dystrophy type 2, MD1 is more severe and may affect lifespan.[2]

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
HPO ID
80%-99% of people have these symptoms
Cardiac conduction abnormality
0031546
Distal muscle weakness
Weakness of outermost muscles
0002460
EMG: myotonic discharges
0100284
Excessive daytime somnolence
Excessive daytime sleepiness
More than typical sleepiness during day

[ more ]

0001262
Myotonia with warm-up phenomenon
0003740
Posterior subcapsular cataract
0007787
30%-79% of people have these symptoms
Abnormal rapid eye movement sleep
0002494
Abnormality of masticatory muscle
0410011
Atrial fibrillation
Quivering upper heart chambers resulting in irregular heartbeat
0005110
Fatigable weakness of bulbar muscles
0030192
Fatigue
Tired
Tiredness

[ more ]

0012378
Foot dorsiflexor weakness
Foot drop
0009027
Hypersomnia
Excessive sleepiness
0100786
Myalgia
Muscle ache
Muscle pain

[ more ]

0003326
Obstructive sleep apnea
0002870
Poor fine motor coordination
0007010
Prolonged PR interval
0012248
Prolonged QRS complex
0006677
5%-29% of people have these symptoms
Abnormality of the cerebral white matter
0002500
Abnormality of the tongue muscle
0040173
Abnormality of thyroid physiology
Abnormal thyroid function
0002926
Alopecia
Hair loss
0001596
Anxiety
Excessive, persistent worry and fear
0000739
Astigmatism
Abnormal curving of the cornea or lens of the eye
0000483
Bilateral ptosis
Drooping of both upper eyelids
0001488
Cerebral cortical atrophy
Decrease in size of the outer layer of the brain due to loss of brain cells
0002120
Cholelithiasis
Gallstones
0001081
Constipation
0002019
Decreased fertility
Abnormal fertility
0000144
Decreased fetal movement
Less than 10 fetal movements in 12 hours
0001558
Decreased serum testosterone level
Decreased serum testosterone levels
Low serum testosterone level
Low serum testosterone levels

[ more ]

0040171
Depressivity
Depression
0000716
Diabetes mellitus
0000819
Diaphragmatic weakness
Weak diaphragm
0009113
Diarrhea
Watery stool
0002014
Distal amyotrophy
Distal muscle wasting
0003693
Dysarthria
Difficulty articulating speech
0001260
Early balding
0002234
Elevated hepatic transaminase
High liver enzymes
0002910
Facial diplegia
0001349
Falls
0002527
Global developmental delay
0001263
Handgrip myotonia
0012899
Hypercholesterolemia
Elevated serum cholesterol
Elevated total cholesterol
Increased total cholesterol

[ more ]

0003124
Hypergonadotropic hypogonadism
0000815
Hyperinsulinemia
0000842
Hypermetropia
Farsightedness
Long-sightedness

[ more ]

0000540
Impaired visuospatial constructive cognition
0010794
Impotence
Difficulty getting a full erection
Difficulty getting an erection

[ more ]

0000802
Insulin resistance
Body fails to respond to insulin
0000855
Intellectual disability, borderline
Mental retardation, borderline
0006889
Intellectual disability, mild
Mental retardation, borderline-mild
Mild and nonprogressive mental retardation
Mild mental retardation

[ more ]

0001256
Intestinal pseudo-obstruction
0004389
Left ventricular systolic dysfunction
0025169
Limited extraocular movements
0007941
Male hypogonadism
Decreased function of male gonad
0000026
Mental deterioration
Cognitive decline
Cognitive decline, progressive
Intellectual deterioration
Progressive cognitive decline

[ more ]

0001268
Mild fetal ventriculomegaly
0010952
Mood changes
Moody
0001575
Myotonia of the jaw
0012901
Myotonia of the upper limb
0012903
Nasogastric tube feeding in infancy
0011470
Neck flexor weakness

Cause

MD1 is caused by a mutation called a CTG trinucleotide repeat in the DMPK gene.[1][2] It is made up of three DNA building blocks (CTG stands for cytosine, thymine, and guanine) that appear multiple times in a row. If the number of CTG repeats is more than 34, it creates an unstable region in the gene.[1][2] Repeats between 35 and 49 are considered premutations. Individuals with CTG repeats in this range do not have symptoms themselves, but their children are at increased risk of inheriting a larger repeat size and thus having symptoms.[2] 

The protein made by the DMPK gene is believed to play a role in communication and impulse transmission within and between cells. It appears to be important for the correct functioning of cells in the heart, brain, and skeletal muscles.[1][2] The more than normal number of CTG repeats leads to the creation of longer and toxic RNA. This causes problems for cells mainly because it traps and disables important proteins.[3] This prevents cells in muscles and other tissues from functioning normally, leading to the signs and symptoms of MD1.[1][2][3]

Treatment

The resources below provide information about treatment options for this condition. If you have questions about which treatment is right for you, talk to your healthcare professional.

Management Guidelines

  • Orphanet Emergency Guidelines is an article which is expert-authored and peer-reviewed that is intended to guide health care professionals in emergency situations involving this condition.

    Organizations

    Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

    Organizations Supporting this Disease

      Organizations Providing General Support

        Learn more

        These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

        Where to Start

        • MedlinePlus Genetics contains information on Myotonic dystrophy type 1. This website is maintained by the National Library of Medicine.
        • The Muscular Dystrophy Association (MDA) provides additional information about myotonic dystrophy. Click on the link to view this information.
        • Myotonic Dystrophy Foundation provides additional information about Myotonic dystrophy type 1.
        • The National Human Genome Research Institute's (NHGRI) website has an information page on this topic. NHGRI is part of the National Institutes of Health and supports research on the structure and function of the human genome and its role in health and disease.

          In-Depth Information

          • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.
          • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
          • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
          • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
          • PubMed is a searchable database of medical literature and lists journal articles that discuss Myotonic dystrophy type 1. Click on the link to view a sample search on this topic.

            Selected Full-Text Journal Articles

              References

              1. Myotonic Dystrophy. Genetics Home Reference. November 2010; https://ghr.nlm.nih.gov/condition/myotonic-dystrophy.
              2. Bird TD. Myotonic Dystrophy Type 1. GeneReviews. October 22, 2015; https://www.ncbi.nlm.nih.gov/books/NBK1165/.
              3. Wahl M. MMD Research: Seeking yo Free Proteins from a 'Toxic Web'. Muscular Dystrophy Assocation (MDA). June 20, 2012; https://www.mda.org/quest/article/mmd-research-seeking-to-free-proteins-from-a-toxic-web.

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