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ACTC1
actin alpha cardiac muscle 1
ACTC1 encodes the primary actin isoform in adult heart muscle, playing an essential role in cardiac contraction and relaxation. The ACTC1 gene provides instructions for producing cardiac alpha-actin, the predominant actin protein in the contractile apparatus of adult heart muscle cells.
ACTC1 is located on the long (q) arm of chromosome 15, at band 15q14. Arm ratio per GRCh38 - banding schematic.
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ACTC1 (actin alpha cardiac muscle 1) encodes the main actin isoform expressed in the working myocardium of the adult human heart [PMID:11735257]. This protein forms thin filaments within cardiac muscle cells, where it interacts with myosin thick filaments to generate the force required for each heartbeat. The gene is located on chromosome 15 and is expressed at high levels specifically in cardiac tissue, distinguishing it from skeletal muscle and smooth muscle actin isoforms encoded by related genes.
Pathogenic variants in ACTC1 are recognised as an established cause of inherited cardiomyopathy [PMID:15322983]. These variants can lead to structural and functional abnormalities of the heart muscle, including hypertrophic cardiomyopathy, dilated cardiomyopathy, left ventricular non-compaction, and restrictive cardiomyopathy. The gene is classified as an ACMG Secondary Findings gene, reflecting the medical importance of identifying pathogenic variants even when genetic testing is performed for unrelated indications. ACTC1-related conditions typically follow an autosomal dominant inheritance pattern, meaning a single altered copy of the gene is sufficient to cause disease.
What the gene does
The ACTC1 protein is a 377-amino-acid globular protein that polymerises to form the thin filaments of the cardiac sarcomere, the fundamental contractile unit of heart muscle. Cardiac alpha-actin accounts for the majority (approximately 80%) of the total actin pool in ventricular myocytes, with the remainder comprised of skeletal alpha-actin during development and in certain disease states. Each actin monomer binds adenosine triphosphate (ATP) or adenosine diphosphate (ADP), and the nucleotide-binding state influences the stability of actin filaments and their interactions with regulatory proteins.
Within the sarcomere, actin filaments anchor at the Z-disc and extend towards the centre of the sarcomere, where they interdigitate with myosin thick filaments. During muscle contraction, myosin heads bind to specific sites on actin monomers and execute a power stroke fuelled by ATP hydrolysis, sliding the thin and thick filaments past one another to shorten the sarcomere. The cycling of myosin binding, force generation, and detachment repeats rapidly during each heartbeat, and the coordinated action of billions of sarcomeres produces the macroscopic contraction of the heart chambers.
Actin filaments also serve as a scaffold for regulatory proteins that control the accessibility of myosin-binding sites in response to calcium signals. Tropomyosin wraps around the actin filament in a helical fashion, and troponin complexes positioned at regular intervals along the filament respond to calcium ions released from intracellular stores during excitation-contraction coupling. When calcium binds to troponin, a conformational change shifts tropomyosin away from the myosin-binding sites on actin, permitting cross-bridge formation and force generation. The precise stoichiometry and spacing of these regulatory components are critical for the finely tuned control of cardiac contractility.
Beyond its structural role in the sarcomere, cardiac actin participates in mechanotransduction pathways that allow heart muscle cells to sense and respond to mechanical stress. Changes in sarcomere length or tension can trigger signalling cascades that ultimately influence gene expression, protein synthesis, and cellular remodelling. Disruption of normal actin function through pathogenic variants may therefore have consequences that extend beyond the immediate mechanical deficit, potentially contributing to maladaptive hypertrophic or dilated remodelling of the heart over time.
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Chromosome location
ACTC1 is located on the long arm of chromosome 15 at cytogenetic band 15q14. The gene spans approximately 3.1 kilobases of genomic DNA and is organised into seven exons, with exon 1 encoding the 5' untranslated region and the start of the coding sequence. The compact structure of the gene reflects the high degree of evolutionary conservation among actin genes across vertebrate species.
The chromosomal region surrounding ACTC1 contains several other genes involved in diverse cellular functions, but none are directly related to the sarcomeric contractile apparatus. The isolated position of ACTC1 on chromosome 15 contrasts with some other sarcomeric protein genes that are clustered together, such as the myosin heavy chain genes on chromosome 14. Regulatory elements controlling ACTC1 expression include cardiac-specific enhancers that restrict transcription predominantly to myocardial tissue during development and throughout adult life.
Protein structure
Cardiac alpha-actin adopts a conserved globular fold common to all actin family members, consisting of four subdomains arranged around a central nucleotide-binding cleft. Cardiac-specific functional domains have not been fully characterised beyond this conserved actin fold. The ATP or ADP molecule sits at the interface between the two major lobes of the protein, and conformational changes associated with nucleotide binding and hydrolysis influence the polymerisation dynamics of actin filaments.
The surface of each actin monomer contains interaction sites for myosin motor domains, as well as binding regions for tropomyosin and other regulatory proteins. Small sequence differences between cardiac alpha-actin and other actin isoforms are concentrated in specific surface loops and are thought to fine-tune the kinetics of myosin binding and the calcium sensitivity of force generation in heart muscle. Post-translational modifications, including acetylation and arginylation, can further modulate actin function, although the full repertoire of modifications and their functional consequences remain areas of active investigation.
Key variants
Pathogenic variants in ACTC1 are predominantly missense changes that alter single amino acids within the actin protein [PMID:10330430]. These substitutions can disrupt normal protein folding, impair polymerisation into thin filaments, or interfere with the binding of regulatory proteins or myosin. The majority of reported pathogenic variants are located in regions of the protein that are critical for filament stability or for interactions with sarcomeric binding partners.
Because ACTC1 follows an autosomal dominant inheritance pattern, a single pathogenic variant is typically sufficient to cause disease. The mutant actin protein may exert a dominant-negative effect by incorporating into filaments and disrupting their normal structure or function, rather than simply reducing the total amount of functional actin. The clinical severity and specific cardiomyopathy phenotype associated with a given variant can vary, even within the same family, suggesting that genetic background and environmental factors influence disease expression.
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.301G>A | p.Glu101Lys | Pathogenic | ★★★☆ | Left ventricular noncompaction 4 |
c.740G>A | p.Gly247Asp | Pathogenic/Likely pathogenic | ★★☆☆ | Hypertrophic cardiomyopathy 11 |
c.866T>C | p.Ile289Thr | Pathogenic/Likely pathogenic | ★★☆☆ | Primary dilated cardiomyopathy |
c.889G>T | p.Ala297Ser | Pathogenic | ★☆☆☆ | Hypertrophic cardiomyopathy 11 |
c.997G>C | p.Ala333Pro | Pathogenic | ★☆☆☆ | Hypertrophic cardiomyopathy 11 |
c.850A>T | p.Ile284Phe | Likely pathogenic | ★★★☆ | not specified |
c.383C>T | p.Thr128Ile | Likely pathogenic | ★★☆☆ | not specified |
c.553C>T | p.Arg185Trp | Likely pathogenic | ★★☆☆ | Primary dilated cardiomyopathy |
c.1121G>A | p.Arg374His | Likely pathogenic | ★☆☆☆ | Arthrogryposis |
c.155A>C | p.Lys52Thr | Likely pathogenic | ★☆☆☆ | Dilated cardiomyopathy 1R |
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 ACTC1 are associated with several forms of inherited cardiomyopathy. Hypertrophic cardiomyopathy, characterised by abnormal thickening of the heart muscle, is among the most frequently reported phenotypes linked to ACTC1 variants. Affected individuals may experience symptoms such as shortness of breath, chest pain, palpitations, or fainting, and are at increased risk of serious cardiac arrhythmias and sudden cardiac death.
Dilated cardiomyopathy, in which the heart chambers enlarge and the muscle weakens, has also been attributed to ACTC1 pathogenic variants. This condition can lead to progressive heart failure, requiring careful monitoring and medical management. Left ventricular non-compaction, a structural abnormality in which the inner layer of the heart muscle has prominent trabeculations, represents another phenotype observed in some families with ACTC1 variants. Rarely, restrictive cardiomyopathy and congenital heart defects such as atrial septal defects have been reported in association with specific ACTC1 variants. The age of onset and severity of symptoms are variable, and some individuals carrying a pathogenic variant may remain asymptomatic for many years or even throughout life.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic ACTC1 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, ACTC1 is included on multiple PanelApp gene panels that guide diagnostic testing for inherited cardiac conditions. The gene holds green (high-evidence) status on the Hypertrophic Cardiomyopathy panel (R131), the Dilated and Arrhythmogenic Cardiomyopathy panel (R132), the Paediatric or Syndromic Cardiomyopathy panel (R135), the Dilated Cardiomyopathy and Conduction Defects panel, the Left Ventricular Noncompaction Cardiomyopathy panel, and the Fetal Anomalies panel (R21).
Green classification on these panels indicates that variants in ACTC1 are routinely analysed when these conditions are suspected, and that pathogenic findings are considered clinically actionable. The inclusion of ACTC1 in the ACMG Secondary Findings list further underscores the importance of reporting pathogenic variants identified incidentally during genome or exome sequencing, as early detection may enable preventive cardiac surveillance and management.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
For individuals known to carry a pathogenic variant in ACTC1, general lifestyle measures that support cardiovascular health are typically recommended. Regular follow-up with a cardiologist experienced in inherited heart conditions is important for monitoring cardiac structure and function over time, as the clinical course can evolve even in individuals who are initially asymptomatic.
Physical activity recommendations are individualised based on the specific type of cardiomyopathy and the severity of cardiac involvement. Some forms of strenuous competitive sport may carry increased risk for individuals with hypertrophic cardiomyopathy due to the potential for exercise-induced arrhythmias. Clinical guidelines often advise a cautious approach to high-intensity exercise, though low-to-moderate intensity activity is generally considered safe and beneficial for overall health when guided by specialist input.
Maintaining a balanced diet, avoiding excessive alcohol consumption, and managing other cardiovascular risk factors such as hypertension and elevated cholesterol may help reduce additional strain on the heart. These general measures are supported by population-level evidence for cardiovascular health, though specific dietary interventions targeting ACTC1-related cardiomyopathy have not been established. Any significant lifestyle changes should be discussed with a healthcare provider familiar with the individual's cardiac status.
Supplement considerations
There is no conclusive evidence that any specific dietary supplement can prevent or treat cardiomyopathy associated with ACTC1 pathogenic variants. Some observational studies have examined the potential role of omega-3 fatty acids, coenzyme Q10, and other supplements in supporting heart function more broadly, but the findings remain inconclusive and do not demonstrate clear benefit for inherited cardiomyopathies caused by sarcomeric gene variants.
Individuals considering the use of supplements should discuss their plans with a healthcare provider before starting any new regimen. Certain supplements can interact with prescription medications used to manage heart conditions, and unregulated products may carry unknown risks. The cornerstone of management for ACTC1-related cardiomyopathy remains evidence-based medical therapies, regular cardiac monitoring, and, when appropriate, interventions such as implantable cardioverter-defibrillators or other devices to reduce the risk of life-threatening arrhythmias.
Any claims that specific supplements can reverse or cure genetic forms of cardiomyopathy should be viewed with scepticism. Families affected by ACTC1 variants are best served by working closely with specialist cardiology and genetics services to ensure comprehensive, personalised care based on current clinical guidelines.
Frequently asked questions
What is the difference between ACTC1 and other actin genes?
ACTC1 encodes cardiac alpha-actin, the predominant actin isoform in adult heart muscle, whereas other actin genes such as ACTA1 encode skeletal muscle actin and ACTG2 encodes smooth muscle actin. These isoforms differ slightly in amino acid sequence and are expressed in specific tissues, reflecting their adaptation to distinct contractile requirements.
How common are pathogenic variants in ACTC1?
Pathogenic variants in ACTC1 are a relatively rare cause of inherited cardiomyopathy, accounting for a small proportion of cases compared to more frequently implicated genes such as MYH7 and MYBPC3. However, ACTC1 variants are well recognised and clinically significant when identified.
Can ACTC1 variants cause symptoms in childhood?
Yes, some individuals with pathogenic ACTC1 variants develop symptoms during childhood or adolescence, although onset in adulthood is also common. The age at which symptoms appear and the severity of disease can vary widely, even within the same family.
Is genetic testing for ACTC1 available on the NHS?
Yes, ACTC1 is included on multiple NHS Genomic Medicine Service gene panels for inherited cardiac conditions. Testing is typically arranged through specialist cardiology or genetics clinics when there is a clinical suspicion of inherited cardiomyopathy.
What does it mean if a family member has an ACTC1 variant?
If a pathogenic variant in ACTC1 is identified in a family member, other relatives may be at risk of inheriting the same variant. Cascade genetic testing and cardiac screening can be offered to at-risk relatives to enable early detection and proactive management if the variant is present.
Does everyone with a pathogenic ACTC1 variant develop heart disease?
Not all individuals carrying a pathogenic ACTC1 variant will develop symptomatic heart disease. Some remain asymptomatic throughout life, a phenomenon known as incomplete penetrance. Regular cardiac monitoring is important even for those without symptoms, as disease can develop or progress over time.