On this page
CALM1
calmodulin 1
CALM1 encodes calmodulin, a calcium-binding protein that regulates cardiac electrical activity and is essential for normal heart rhythm. The CALM1 gene provides instructions for making calmodulin, a small calcium-sensing protein found in every cell.
CALM1 is located on the long (q) arm of chromosome 14, at band 14q32.11. Arm ratio per GRCh38 - banding schematic.
Explore chromosome 14 in the library →Overview
The CALM1 gene encodes calmodulin, one of the most highly conserved proteins in evolution and a central regulator of calcium signalling. Present in all eukaryotic cells, calmodulin functions as a calcium sensor that changes shape when calcium ions bind to it, enabling the protein to activate or inhibit more than 300 different target proteins throughout the cell. This calcium-dependent switching mechanism allows cells to translate transient calcium signals into specific biological responses, from muscle contraction and neurotransmitter release to gene transcription and cell division.
In humans, calmodulin is encoded by three separate genes - CALM1, CALM2, and CALM3 - each located on a different chromosome but all producing identical 149-amino-acid proteins. This genetic redundancy reflects calmodulin's fundamental importance to cellular function. Despite producing the same protein sequence, pathogenic variants in CALM1 account for a substantial proportion of calmodulin-related cardiac arrhythmias, suggesting that the three genes may contribute differently to calmodulin expression in specific tissues.
Clinical interest in CALM1 centres on its role in cardiac electrophysiology. Calmodulin regulates multiple ion channels and calcium-handling proteins that control the heartbeat, and even subtle alterations to its calcium-sensing properties can disrupt cardiac rhythm. Pathogenic variants in CALM1 are recognised causes of severe inherited arrhythmia syndromes that typically present in childhood and carry substantial risk of sudden cardiac death without appropriate management. Understanding CALM1 function has therefore become essential for identifying individuals at risk and implementing potentially life-saving interventions.
What the gene does
Calmodulin operates as a high-affinity calcium-binding protein that undergoes conformational changes upon binding calcium ions, transforming from a compact, inactive state to an extended, active configuration. This calcium-dependent shape change exposes hydrophobic surfaces that allow calmodulin to recognise and bind to specific sequences within target proteins. Through this mechanism, calmodulin serves as an intermediary that couples transient increases in intracellular calcium concentration to the activation or inhibition of enzymes, ion channels, and structural proteins.
In cardiac myocytes, calmodulin regulates several ion channels critical for the cardiac action potential. The protein modulates the L-type calcium channel, which mediates calcium entry during the plateau phase of the action potential, and also regulates the ryanodine receptor, which controls calcium release from intracellular stores. Calmodulin's interaction with these channels ensures proper timing and magnitude of calcium transients, which are essential for coordinated cardiac contraction and electrical repolarisation. Disruption of these regulatory interactions can prolong action potential duration and create conditions conducive to dangerous arrhythmias.
Calmodulin also activates calcium/calmodulin-dependent protein kinase II (CaMKII), a multifunctional enzyme that phosphorylates numerous cardiac proteins involved in excitation-contraction coupling. This activation represents a key step in translating calcium signals into longer-lasting cellular responses. In addition, calmodulin regulates adenylyl cyclase and phosphodiesterase enzymes that control cyclic AMP levels, linking calcium and cyclic AMP signalling pathways. Through these diverse interactions, calmodulin coordinates multiple aspects of cardiac function in response to physiological demands.
Beyond the cardiovascular system, calmodulin participates in neurotransmitter synthesis and release, smooth muscle contraction, cytoskeletal organisation, and cell-cycle progression. The protein's ability to regulate such diverse processes stems from its capacity to bind more than 300 different target proteins, each recognised through specific sequence motifs. This versatility makes calmodulin one of the most functionally important proteins in human biology, though pathogenic variants causing disease primarily manifest through cardiac dysfunction, likely because the heart is particularly sensitive to perturbations in calcium handling.
Video: Genetics 101
Chromosome location
CALM1 is located on chromosome 14 at position q32.11, in the long arm's third cytogenetic band of region 3, sub-band 2, sub-sub-band 1. The gene spans approximately 11 kilobases of genomic DNA and contains six exons separated by five introns. Despite its modest genomic footprint, CALM1 exhibits highly efficient transcription and translation, contributing substantially to total cellular calmodulin levels.
The chromosomal location of CALM1 differs from CALM2 (chromosome 2p21) and CALM3 (chromosome 19q13.32), reflecting the evolutionary history of these genes, which arose through duplication events. This dispersed genomic organisation ensures that a single chromosomal deletion cannot eliminate all calmodulin production, though heterozygous pathogenic variants producing abnormal protein can still cause disease through dominant-negative mechanisms. This demonstrates that normal calmodulin function requires precise control of protein structure and that the three genes cannot fully compensate for variants that produce abnormal protein products.
Protein structure
Calmodulin is a compact, 149-amino-acid protein organised into two globular domains connected by a flexible central linker. Each globular domain contains a pair of EF-hand calcium-binding motifs, specialised helix-loop-helix structures that coordinate calcium ions through conserved acidic residues. The N-terminal domain comprises EF-hand 1 (amino acids 8-43) and EF-hand 2 (amino acids 44-79), whilst the C-terminal domain contains EF-hand 3 (amino acids 81-116) and EF-hand 4 (amino acids 117-149).
Each EF-hand motif binds a single calcium ion with high affinity and selectivity. The four EF-hands cooperate to enable calmodulin to sense calcium concentration changes across the physiologically relevant range, typically from resting levels around 100 nanomolar to peak levels exceeding 1 micromolar during cellular activation. Calcium binding triggers a dramatic conformational change in which the two globular domains separate and rotate, exposing hydrophobic patches that serve as docking sites for target proteins.
The flexible linker region between the two globular domains allows calmodulin to adopt multiple conformations and wrap around target protein sequences in different configurations. This structural plasticity enables calmodulin to recognise diverse binding partners despite their lack of strict sequence similarity. The C-terminal region including amino acids 77-149 has been identified as necessary and sufficient for interaction with PCP4, a brain-specific calmodulin-binding protein, illustrating how different regions of calmodulin engage specific targets.
Pathogenic variants cluster within the EF-hand domains, where single amino acid substitutions can impair calcium binding affinity, alter the calcium-dependent conformational change, or disrupt interactions with target proteins. Because each of the four EF-hands contributes to overall calcium sensitivity, variants in any of these domains can shift calmodulin's calcium-sensing properties and produce cardiac dysfunction.
Key variants
Pathogenic variants in CALM1 predominantly comprise missense changes that alter single amino acids within the calcium-binding EF-hand domains. Unlike many disease genes where loss-of-function variants predominate, CALM1-related arrhythmias arise from gain-of-function or dominant-negative mechanisms, in which the altered calmodulin protein actively disrupts normal calcium signalling rather than simply reducing protein levels. This explains why heterozygous variants are sufficient to cause disease despite the presence of normal protein produced from the other CALM1 allele and from CALM2 and CALM3.
The majority of reported pathogenic variants affect residues directly involved in coordinating calcium ions within the EF-hand loops or residues that stabilise the calcium-bound conformation. These variants typically reduce calcium-binding affinity, meaning that mutant calmodulin requires higher calcium concentrations to activate properly. In cardiac myocytes, this impaired calcium sensing disrupts the regulation of ion channels and calcium-handling proteins, prolonging action potential duration and increasing susceptibility to triggered arrhythmias.
A smaller number of pathogenic variants affect residues outside the calcium-binding sites but within regions that undergo conformational changes or interact with target proteins. These variants can alter calmodulin's ability to activate or inhibit specific targets without necessarily changing calcium affinity. Genotype-phenotype studies suggest that the specific location and biochemical consequence of a variant influence clinical presentation, with some variants more strongly associated with long QT syndrome and others predominantly causing catecholaminergic polymorphic ventricular tachycardia, though substantial overlap exists.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.293A>G | p.Asn98Ser | Pathogenic/Likely pathogenic | ★★☆☆ | Cardiovascular phenotype |
c.389A>G | p.Asp130Gly | Pathogenic/Likely pathogenic | ★★☆☆ | Long QT syndrome 14 |
c.424T>C | p.Phe142Leu | Pathogenic | ★★☆☆ | not provided |
c.270C>G | p.Phe90Leu | Pathogenic | ★☆☆☆ | Catecholaminergic polymorphic ventricular tachycardia 4 |
c.286G>T | p.Asp96Tyr | Pathogenic | ★☆☆☆ | Catecholaminergic polymorphic ventricular tachycardia 4 |
c.389A>T | p.Asp130Val | Pathogenic | ★☆☆☆ | Long QT syndrome 14 |
c.394G>A | p.Asp132Asn | Pathogenic | ★☆☆☆ | Long QT syndrome 14 |
c.395A>G | p.Asp132Gly | Pathogenic | ★☆☆☆ | Catecholaminergic polymorphic ventricular tachycardia 4 |
c.395A>T | p.Asp132Val | Pathogenic | ★☆☆☆ | Long QT syndrome 14 |
c.419A>T | p.Glu140Val | Likely pathogenic | ★★☆☆ | not provided |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Pathogenic variants in CALM1 cause severe cardiac arrhythmia syndromes inherited in an autosomal dominant pattern, meaning that a variant in one copy of the gene is sufficient to cause disease. The two principal conditions are long QT syndrome and catecholaminergic polymorphic ventricular tachycardia, both of which typically present in childhood and carry significant risk of sudden cardiac death. Long QT syndrome is characterised by prolongation of the QT interval on electrocardiogram, reflecting delayed ventricular repolarisation that predisposes to a specific type of ventricular arrhythmia called torsades de pointes. Catecholaminergic polymorphic ventricular tachycardia manifests as exercise- or emotion-triggered ventricular arrhythmias in individuals with structurally normal hearts and normal resting electrocardiograms.
CALM1-related arrhythmias tend to present earlier and behave more severely than forms caused by variants in other genes associated with these conditions. Many affected individuals experience their first cardiac event, such as syncope or cardiac arrest, during the first year of life. The severity likely reflects calmodulin's central role in coordinating multiple aspects of cardiac calcium handling, such that even partial disruption of calmodulin function affects numerous downstream targets simultaneously. Recognition of CALM1 involvement has important clinical implications because affected individuals may require more aggressive management, including early implantable cardioverter-defibrillator placement and intensive beta-blocker therapy, compared to individuals with other genetic causes of inherited arrhythmia.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic CALM1 variants typically follow autosomal dominant inheritance.
Each child has a 50% chance of inheriting the pathogenic variant, regardless of sex.
UK clinical status
Within the NHS Genomic Medicine Service, CALM1 features on two national clinical gene panels maintained through the PanelApp resource. The gene holds green (high-evidence) status on both the Catecholaminergic Polymorphic VT panel (version 129) and the Long QT Syndrome panel (version 127), reflecting strong evidence supporting its role in these conditions. Green classification indicates that evidence supports routine testing for CALM1 variants in individuals meeting clinical diagnostic criteria for these arrhythmia syndromes.
These panel memberships guide clinical genetic testing pathways across NHS laboratories. When a patient presents with clinical features of long QT syndrome or catecholaminergic polymorphic ventricular tachycardia, cardiologists and clinical geneticists can request targeted gene panel testing that includes CALM1 alongside other established arrhythmia genes. Identification of a pathogenic CALM1 variant confirms the genetic diagnosis, enables cascade testing of at-risk relatives, and informs clinical management decisions. The NHS Genomic Medicine Service provides access to genetic counselling to support families through the testing process and interpretation of results.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
For individuals with pathogenic CALM1 variants, lifestyle modifications focus on reducing triggers for cardiac arrhythmias and optimising cardiovascular health. Research into catecholaminergic polymorphic ventricular tachycardia suggests that avoiding strenuous physical exertion and competitive sports can reduce arrhythmia risk, as exercise-induced adrenaline surges may trigger dangerous heart rhythms in susceptible individuals. Some cardiology guidelines recommend restricting participation in competitive athletics for those with certain inherited arrhythmia syndromes, though individual recommendations should be made in consultation with a specialist cardiac electrophysiologist who can assess personal risk.
Stress management represents another important consideration, given that emotional stress can trigger arrhythmic events through catecholamine release. Whilst general population evidence suggests that adequate sleep and stress management support cardiovascular health, specific evidence for CALM1-related conditions remains limited and these measures complement rather than substitute medical management. Swimming without supervision may pose particular risks for individuals with long QT syndrome or catecholaminergic polymorphic ventricular tachycardia, as loss of consciousness in water can be fatal; specialist cardiac opinion should guide decisions about aquatic activities.
Maintaining overall cardiovascular health through a balanced diet and avoiding risk factors such as smoking remains important for the general population, though no specific dietary pattern has been shown to prevent arrhythmias in individuals with CALM1 variants. Some medications and supplements can prolong the QT interval and should typically be avoided by those with long QT syndrome; individuals with CALM1-related arrhythmias should consult their cardiologist before starting any new medication. These lifestyle considerations complement medical management and do not substitute for specialist cardiac care.
Supplement considerations
Currently, no nutritional supplements have been demonstrated to prevent or ameliorate cardiac arrhythmias caused by CALM1 variants. Calmodulin's function depends on its three-dimensional structure and calcium-binding properties, which cannot be modified through dietary supplementation. Some commercially available supplements claim to support cardiovascular health or cellular calcium handling, but there is no conclusive evidence that such products influence outcomes in inherited arrhythmia syndromes.
Magnesium supplementation is sometimes used in the acute management of certain arrhythmias, particularly torsades de pointes in long QT syndrome, but this represents an emergency medical intervention rather than a preventive strategy. Population studies suggest that adequate dietary magnesium intake may support general cardiovascular health, but individuals with CALM1 variants should not self-prescribe magnesium supplements without discussing this with their cardiologist, as inappropriate supplementation could potentially interfere with prescribed medications or complicate clinical assessment.
Similarly, whilst omega-3 fatty acids have been studied for various cardiovascular conditions, evidence does not support their use specifically for preventing arrhythmias in genetic conditions affecting calcium signalling. Any individual with a CALM1 variant considering nutritional supplements should first consult their specialist cardiac team, as the primary management for these conditions involves anti-arrhythmic medications, beta-blockers, and potentially device therapy, all of which require careful monitoring and should not be supplemented or substituted without medical guidance.
Frequently asked questions
Why are there three calmodulin genes if they make the same protein?
The three calmodulin genes (CALM1, CALM2, CALM3) arose through evolutionary gene duplication and are located on different chromosomes. This genetic redundancy likely ensures adequate calmodulin production even if one gene is damaged, reflecting how essential calmodulin is for cell survival. Despite producing identical proteins, the three genes may be regulated differently across tissues, and pathogenic variants in each can cause disease.
How do CALM1 variants cause heart rhythm problems?
Pathogenic CALM1 variants typically impair calmodulin's ability to sense calcium properly, disrupting its regulation of cardiac ion channels and calcium-release proteins. This leads to prolonged action potentials and abnormal calcium cycling in heart muscle cells, creating electrical instability that can trigger life-threatening arrhythmias. Even subtle changes to calmodulin's structure can have profound effects because the protein regulates so many critical cardiac targets simultaneously.
At what age do CALM1-related arrhythmias typically appear?
CALM1-related cardiac arrhythmias frequently present in infancy or early childhood, often earlier than arrhythmias caused by variants in other genes. Many affected individuals experience their first cardiac event, such as syncope or cardiac arrest, within the first year of life, though presentation can occasionally occur later. The early onset and severity necessitate prompt recognition and specialist cardiac management.
Can genetic testing for CALM1 be arranged through the NHS?
Yes, CALM1 genetic testing is available through the NHS Genomic Medicine Service for individuals meeting clinical criteria for long QT syndrome or catecholaminergic polymorphic ventricular tachycardia. Cardiologists or clinical geneticists can request testing using national gene panels that include CALM1. Genetic counselling is provided to support families through the testing process and interpretation of results.
If one parent has a CALM1 variant, what is the chance of passing it to children?
CALM1-related arrhythmias follow an autosomal dominant inheritance pattern, meaning each child of an affected parent has a 50% chance of inheriting the pathogenic variant. However, some CALM1 variants arise as new (de novo) changes not inherited from either parent. Families concerned about inheritance should discuss genetic counselling and predictive testing options with their clinical genetics service.
Is calmodulin only important in the heart?
No, calmodulin functions in virtually every cell type and regulates hundreds of different proteins involved in muscle contraction, neurotransmission, metabolism, and cell division. However, pathogenic CALM1 variants predominantly cause cardiac symptoms, likely because heart muscle is exceptionally sensitive to disruptions in calcium signalling. The heart's continuous rhythmic activity and tight control of electrical timing make it particularly vulnerable to even small changes in calmodulin function.