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Features include always present findings: Myotonia with warm-up phenomenon; and common findings: Muscle stiffness, Myotonia, Handgrip myotonia, and Percussion myotonia and others. 10 total HPO annotations.
Organ System | Phenotype Count | Example Features |
|---|---|---|
Muscles | 9 | EMG: myotonic runs, Muscle stiffness, Myotonia with warm-up phenomenon |
Arms and legs | 1 | Handgrip myotonia |
Bones and joints | 1 | Skeletal muscle hypertrophy |
Myotonia congenita is characterized by muscle stiffness present from childhood; all striated muscle groups including the extrinsic eye muscles, facial muscles, and tongue may be involved. Stiffness is relieved by repeated contractions of the muscle (the "warm-up" phenomenon). Muscles are usually hypertrophic. Whereas autosomal recessive (AR) myotonia congenita is often associated with more severe manifestations (such as progressive, minor distal weakness and attacks of transient weakness brought on by movement after rest), autosomal dominant (AD) myotonia congenita is not. A study of more than 300 affected individuals from the UK revealed a ratio of 70% AR myotonia congenita to 30% AD myotonia congenita among families with a molecularly confirmed diagnosis . Comparable distribution has been identified in Italian , Spanish , and German cohorts ; in contrast, AD myotonia congenita is more common than AR myotonia congenita in Denmark . Table 2. Myotonia Congenita: Comparison of Select Features by Mode of Inheritance
Feature | AR Myotonia Congenita | AD Myotonia Congenita |
|---|---|---|
Age of onset | Early childhood | Early infancy |
Muscle stiffness | Generalized, legsarms | Generalized, armslegs |
Muscle hypertrophy | Generalized | Generalized |
Pain | Very common | Common |
Transient muscle weakness | Common | Not present |
Distal muscle weakness | Rarely | Not present |
Proximal muscle weakness | Rarely | Not present Age of onset is variable. In AD myotonia congenita, onset of symptoms is usually in infancy or early childhood. In AR myotonia congenita, the average age of onset is slightly older. In both conditions, onset may be as late as the third or fourth decade of life. |
Source: GeneReviews — "Myotonia Congenita"
CLCN1 encodes chloride voltage-gated channel 1 (988 aa). Voltage-gated chloride channel involved in skeletal muscle excitability. Highest expression in Muscle Skeletal (10.2 TPM) and Testis (2.8 TPM).
Myotonia congenita, autosomal dominant is associated with mutations in the CLCN1 gene on chromosome 7.
The CLCN1 protein participates in CLCN1/2/KA/KB transport cytosolic Cl- to extracellular region pathway.
CLCN1 is classified as a druggable target (Druggable Genome, Ion Channel, and Transporter categories) with score 0.0.
Pathogenic variants identified in AD myotonia congenita can be associated with variable expression and reduced penetrance [, , , ].
Source: GeneReviews — "Myotonia Congenita"
No consensus clinical diagnostic criteria for myotonia congenita (sometimes referred to as "chloride channel myotonia") have been published.
Myotonia congenita should be suspected in individuals with the following clinical and laboratory findings.
Clinical findings and medical history
Episodes of muscle stiffness (myotonia) or cramps beginning in early childhood
Alleviation of stiffness by brief exercise (known as the "warm-up" effect)
Myotonic contraction elicited by percussion of muscles
Laboratory findings
Source: GeneReviews — "Myotonia Congenita"
The differential diagnosis of myotonia congenita includes other disorders in which myotonia is a prominent finding. Myotonia congenita can usually be distinguished from these disorders based on the following:
Factors that provoke or alleviate myotonia
Presence or absence of extramuscular manifestations
Findings on electrodiagnostic and molecular genetic testing
Source: GeneReviews — "Myotonia Congenita"
Genetic testing for CLCN1 is available. Testing is considered confirmatory for diagnosis.
Biomarker and diagnostic research for myotonia congenita, autosomal dominant has been reported in the published literature.
No approved treatments are currently available for myotonia congenita, autosomal dominant. The disease remains an area of unmet medical need.
No specific clinical practice guidelines for myotonia congenita have been published. However, a general guideline on clinical presentation and management of nondystrophic myotonias is available .
To establish the extent of disease and needs in an individual diagnosed with myotonia congenita, the following evaluations (if not performed as part of the evaluation that led to the diagnosis) are recommended:
Consultation with a neurologist or other relevant specialist to evaluate the need for pharmacologic treatment. Severity of myotonia can be assessed by a myotonia questionnaire (e.g., the Myotonia Behavior Scale ) and by timed assessments of myotonia, for instance, time to open tightly closed eyes, time to open a clinched hand, testing of myotonia walking on a staircase, or a timed-up-and-go test.
Consultation with a medical geneticist, certified genetic counselor, or certified advanced genetic nurse to inform affected individuals and their families about the nature, mode of inheritance, and implications of myotonia congenita in order to facilitate medical and personal decision making
Some individuals with minor complaints may only need to accommodate their activities and lifestyles to reduce symptoms . Exercise temporarily alleviates myotonia (the "warm-up" effect). Note that a long-term beneficial effect of gymnastics is doubtful, as a small training study of six individuals with myotonia congenita showed good imp...
Source: GeneReviews — "Myotonia Congenita"
In general, anesthesia should be used with caution . Particular care must be taken with the use of depolarizing muscle relaxants during anesthesia because they may cause adverse anesthesia-related events. Because life-threatening muscle spasms and secondary ventilation difficulties occurred following a preoperative injection of suxamethonium, recommended that suxamethonium be avoided in individuals with myotonia congenita. Note: Non-depolarizing muscle relaxants appear to act normally in individuals with myotonia congenita but do not counteract a myotonic response caused by suxamethonium . In rare cases, injections of adrenaline or selective beta-adrenergic agonists in high doses may aggravate myotonia. The beta-antagonist propranolol has likewise been reported to worsen myotonia . Accordingly, beta-agonists and beta-antagonists should be used with caution, and particular care should be taken with the use of intravenous fenoterol or ritodrine.
Source: GeneReviews — "Myotonia Congenita"
Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.
Source: GeneReviews — "Myotonia Congenita"
View trials for myotonia congenita, autosomal dominant
Phenotype severity distribution: 1 always present feature, 5 common features.
No clinical trials have been registered for myotonia congenita, autosomal dominant.
52 publications have been identified in PubMed for myotonia congenita, autosomal dominant. Research spans Basic Science / Preclinical (38%), Case Report / Case Series (31%), and Review / Meta-Analysis (15%).
Research Type | Count | % of Total |
|---|---|---|
Laboratory research | 20 | 38% |
Patient case studies | 16 | 31% |
Research summaries | 8 | 15% |
Disease patterns and progression | 3 | 6% |
Testing and diagnosis research | 2 | 4% |
New treatment approaches | 2 | 4% |
Clinical study results | 1 | 2% |
Spicer D (2026). [PMID: 41791994](https://pubmed.ncbi.nlm.nih.gov/41791994/). *Neuromuscul Disord*. [Case Report / Case Series]
Sanaulla S (2026). [PMID: 42021513](https://pubmed.ncbi.nlm.nih.gov/42021513/). *Ann Afr Med*. [Case Report / Case Series]
Kubota T (2026). [PMID: 41485931](https://pubmed.ncbi.nlm.nih.gov/41485931/). *Nihon yakurigaku zasshi. Folia pharmacologica Japonica*. [Basic Science / Preclinical]
Amara A (2026). [PMID: 41627073](https://pubmed.ncbi.nlm.nih.gov/41627073/). *Journal of neuromuscular diseases*. [Case Report / Case Series]
Śliwińska B (2026). [PMID: 41603675](https://pubmed.ncbi.nlm.nih.gov/41603675/). *Neurol Neurochir Pol*. [Review / Meta-Analysis]
Shutes TK (2026). [PMID: 41524695](https://pubmed.ncbi.nlm.nih.gov/41524695/). *A&A practice*. [Basic Science / Preclinical]
Kinoshita M (2026). [PMID: 41442183](https://pubmed.ncbi.nlm.nih.gov/41442183/). *Journal of neurophysiology*. [Review / Meta-Analysis]
Katirji B (2026). [PMID: 42124386](https://pubmed.ncbi.nlm.nih.gov/42124386/). *Muscle Nerve*. [Review / Meta-Analysis]
Iturrate A (2026). [PMID: 41023410](https://pubmed.ncbi.nlm.nih.gov/41023410/). *European journal of human genetics : EJHG*. [Basic Science / Preclinical]
Crayle JI (2026). [PMID: 42108746](https://pubmed.ncbi.nlm.nih.gov/42108746/). *Muscle Nerve*. [Diagnostic / Biomarker]
Data assembled from 6 of 12 sources · Last updated Sep 20, 2026, 5:37 PM UTC
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