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Myotonic dystrophy is a group of progressive inherited neuromuscular disorders characterized by muscle wasting, hypotonia, myotonia, cataracts, cardiac conduction defects, and endocrine abnormalities. The condition is classified as uncommon, with a prevalence of approximately 1 to 9 per 100,000 individuals. It encompasses several clinical subtypes, including myotonic dystrophy type 1 (DM1), myotonic dystrophy type 2 (DM2), and congenital, childhood-onset, juvenile-onset, adult-onset, and late-onset forms. DM1, the most extensively characterized subtype, results from CTG trinucleotide repeat expansion in the DMPK gene. Penetrance of DM1 is high, approaching 100% by age 50 years when all manifestations are considered. Onset across the spectrum ranges from the neonatal period in the most severe congenital form to subtle findings in mid-to-late adulthood in the mildest presentations.
Built from Human Phenotype Ontology (HPO) phenotype annotations and GeneReviews clinical descriptions. Features represent findings documented across known cases — not an exhaustive list of possible symptoms.
Myotonic dystrophy type 1 (DM1) is a systemic disease potentially affecting nearly every organ system. Clinical findings span a continuum from mild to severe, with three overlapping phenotypes recognized: mild, classic, and congenital, broadly correlating with CTG repeat size. In the mild form, the predominant findings are cataracts and mild myotonia, with onset typically between 20 and 70 years. In the classic form, weakness—particularly of distal muscles of the leg, hand, neck, and face—myotonia, cataracts, premature balding, and cardiac arrhythmia are prominent features. Myotonia, characterized by sustained muscle contraction and impaired relaxation (including grip myotonia and percussion myotonia), is a defining clinical feature. Congenital DM1 is the most severe form, presenting in the neonatal period with hypotonia and respiratory involvement. Excessive daytime sleepiness is a frequent additional finding across phenotypes. Cardiac involvement, including arrhythmias capable of causing sudden death, is a significant source of morbidity. Endocrinopathies including testosterone deficiency in males may occur. Pain is a recognized manifestation across DM1 phenotypes.
Genetic Landscape
Assembled from HGNC gene records, ClinGen gene-disease validity evidence, and ClinVar pathogenic variant data. Validity classifications reflect the strength of published evidence linking each gene to this disease.
The most well-characterized form, DM1, results from a CTG trinucleotide repeat expansion in the DMPK gene. This expansion exhibits anticipation—the tendency for repeat size to increase across generations—which correlates broadly (though imperfectly) with clinical severity. CTG repeat sizes in DM1 range from premutation (35–49 repeats, asymptomatic but transmissible) through mild (approximately 50–150 repeats), classic (approximately 100 repeats and above), to congenital (large expansions). The molecular mechanism involves aberrant sequestration of RNA-binding proteins by the expanded CUG repeat RNA, disrupting alternative splicing in multiple organ systems and producing the characteristic multisystem phenotype. DM2 and other subtypes of myotonic dystrophy involve distinct molecular mechanisms; their causative genes are not captured in the certified packet for this umbrella entry.
Diagnosis
Drawn from GeneReviews diagnostic guidelines, newborn screening panel status (RUSP), and ClinGen gene-disease validity classifications. Reflects current clinical evidence and consensus where available.
DM1 is suspected in adults presenting with distal muscle weakness, myotonia, and posterior subcapsular cataracts. In neonates, hypotonia with respiratory compromise and a relevant family history raises the diagnosis. Molecular genetic testing to detect CTG repeat expansion in DMPK confirms DM1. Repeat size is assessed by PCR-based methods combined with Southern blot analysis for large expansions. Posterior subcapsular cataracts are detectable by slit-lamp examination as red and green iridescent opacities. Cardiac evaluation with electrocardiography is part of the diagnostic workup given the risk of arrhythmia. Myotonic dystrophy type 2 requires testing for a distinct repeat expansion and may be considered when clinical findings are suggestive but DM1 testing is negative.
Treatment
Compiled from FDA-approved drug records, orphan drug designations, and FDA Adverse Event Reporting System (FAERS) safety data. GeneReviews management guidance is included where available.
No disease-modifying therapy exists for the progressive muscle weakness characteristic of myotonic dystrophy. Management is supportive and multidisciplinary. For myotonia in DM1—typically mild to moderate and often not requiring treatment—mexiletine has been reported effective and safe for symptomatic control; carbamazepine has been used anecdotally. Pain management approaches documented for DM1 include mexiletine, gabapentin, nonsteroidal anti-inflammatory drugs, low-dose steroids, and tricyclic antidepressants as part of comprehensive programs. Cardiac arrhythmia risk in DM1 is a documented source of morbidity; electrocardiographic abnormalities are addressed through cardiology evaluation. Cataracts, when vision-impairing, are addressed surgically, with recurrence after surgery noted. Assistive devices including ankle-foot orthoses and wheelchairs address progressive mobility limitations. Hypothyroidism and statin use have been associated with increased weakness in DM1 and may be identified as contributing factors. Males with symptomatic low testosterone may be assessed for hormone replacement. Consensus-based care recommendations for adults and for persons with congenital- and childhood-onset DM1 have been published.
Based on GeneReviews surveillance recommendations, HPO phenotype frequency and severity annotations, and published prevalence estimates from Orphanet and OMIM.
The clinical course of myotonic dystrophy varies by phenotype and subtype. In the mild DM1 form, average age of death is approximately 60 years or may approach a normal life span. In the classic DM1 phenotype, cardiac arrhythmias represent a significant and potentially fatal complication; fatal arrhythmias can occur before other overt symptoms become apparent. The congenital form is associated with significant neonatal morbidity. Disease duration and rate of progression vary considerably among individuals across all phenotypes.
Research Landscape
Sourced from ClinicalTrials.gov and PubMed. Publication types are classified using NLM-curated article metadata; research type breakdowns reflect the nature of published work for this disease.
Myotonic dystrophy has 51 active clinical trials, with substantial activity focused on DM1. A Phase 3 study of zeleciment basivarsen (DYNE-101, Dyne Therapeutics, NCT07486934) targeting the DM1 molecular mechanism is recruiting, with completion expected in 2029. A Phase 2 study of PGN-EDODM1 (PepGen Inc., NCT06667453) is recruiting through 2027. A Phase 1/2 study of VX-670 (Vertex Pharmaceuticals, NCT06185764) is enrolling adults with DM1 through 2027. Natural history and biomarker studies include the long-running END-DM1 program at Virginia Commonwealth University (NCT03981575 and NCT07700225, active through 2026–2032) and a pediatric endpoint study (NCT05224778). Additional active work spans personalized neuromuscular training (Oslo University Hospital, NCT06708468), congenital DM genetic determinants (University of Rochester, NCT07630389), and an ambispective natural history registry study (Lupin Ltd., NCT07732439).
Data assembled from 6 of 12 sources · Last updated Sep 19, 2026, 3:00 PM UTC
Diseases are connected by shared genes, phenotypes, therapeutic targets, and MONDO disease hierarchy. The Rare badge reflects Kisho's rarity classification — scored from authoritative sources including OMIM, Orphanet, orphan drug designations, clinical trial activity, and published prevalence data.
While Novartis’ antibody-oligonucleotide conjugate failed to significantly improve hand function in patients with myotonic dystrophy type 1, the asset nevertheless showed signs of clinical activity in secondary and exploratory measures.
Z-basivarsen has been granted Breakthrough Therapy, Orphan Drug and Fast Track designations by the U.S. Food and Drug Administration (FDA), as well as Orphan Drug designation from the European Medicines Agency (EMA) and the Ministry of Health, Labour and Welfare (MHLW) in Japan for the treatment ... Z-basivarsen has been granted Breakthrough Therapy, Orphan Drug and Fast Track designations by the U.S. Food and Drug Administration (FDA), as well as Orphan Drug designation from the European Medicines Agency (EMA) and the Ministry of Health, Labour and Welfare (MHLW) in Japan for the treatment of DM1. - Data from a pooled dose group of participants initially enrolled in the multiple ascending dose portion of the trial to be compared against a matched... Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various important factors, including: uncertainties inherent in the identification and development of product candidates, including the initiation and completion of preclinical studies and clinical trials; uncertainties as to the availability and timing of results from preclinical studies and clinical trials; the timing of and Dyne’s ability to enroll patients in clinical trials; whether results from preclinical studies and initial data fro September 08, 2026 07:51 ET | Source: Dyne Therapeutics, Inc.
PepGen's mid-stage study for myotonic dystrophy has been placed on a partial hold by the FDA due to concerns over preclinical data submitted in mid-2024. Analysts describe the timing of this decision as 'odd' and are closely monitoring the situation.
An investigational antibody–... MARINA clinical trial (NCT05027269). Results from the study were published in The New England Journal of Medicine. Steven W. Pipe, MD, discussed the potential of bringing hemophilia B gene therapy etranacogene dezaparvovec (marketed as Hemgenix) to younger patients. Currently the therapy is only FDA-approved for patients aged 18 years and older. Since 2008, the last day of February has been observed as Rare Disease Day by the ... An investigational antibody–oligonucleotide conjugate (AOC), delpacibart etedesiran (AOC 1001; del-desiran), demonstrated skeletal muscle delivery of small interfering RNA (siRNA) and reductions in mutant DMPK messenger RNA (mRNA) in adults with myotonic dystrophy type 1 (DM1) in the phase 1/2 MARINA clinical trial (NCT05027269). Results from the study were published in The New England Journal of Medicine. Steven W. Pipe, MD, discussed the potential of bringing hemophilia B gene therapy etranacogene dezaparvovec (marketed as Hemgenix) to younger patients. Currently the therapy is only FDA-approved for patients aged 18 years and older. Since 2008, the last day of February has been observed as Rare Disease Day by the patient and clinician communities. The list includes items related to several gene therapy products for rare disease indications. For the month of February, as part of its Clinical Trial in Focus series, NeurologyLive spotlighted the phase 3 MAGNITUDE-2 trial (NCT06672237), assessing Intellia Therapeutics’ investigational gene therapy nexiguran ziclumeran (nex-z) for patients with hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN), a rare genetic neuromuscular condition. Catch up on the latest news, breakthroughs, and announcements from biotechnology companies making advancements in cell and gene therapies. In a Type A meeting with uniQure regarding the path forward for the company’s investigational Huntington disease gene therapy AMT-130, the FDA reaffirmed its position previously · expressed in a pre–biologics license application (preBLA) meeting last year that data from phase 1/2 clinical trials would not be sufficient to support a BLA for the product. Instead, the FDA “strongly recommended” in the Type A meeting the uniQure carry out a “prospective, randomized, double-blind, sham surgery-controlled” phase 3 clinical trial.
