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Classifications

Harrison's Chapter

Channelopathy

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Mappings

MONDO

MONDO:0008222 Andersen-Tawil syndrome

MONDO:0008222 is the primary disease term for this entry, cross-referenced to OMIM:170390 and Orphanet:37553 with KCNJ2 as the asserted causal gene.

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Inheritance

1

Autosomal Dominant HP:0000006

ATS is inherited in an autosomal dominant manner with variable expressivity and incomplete penetrance. Up to half of affected individuals carry a de novo pathogenic variant, so a negative family history does not exclude the diagnosis. Expressivity is strikingly variable even within a single family, and not all affected individuals manifest the complete triad.

Autosomal dominant inheritance

Show evidence (4 references)

PMID:20301441 SUPPORT Human Clinical

"ATS is inherited in an autosomal dominant manner. At least 50% of individuals diagnosed with ATS have an affected parent. Up to 50% of affected individuals have ATS as the result of a de novo pathogenic variant."

GeneReviews states the autosomal dominant inheritance pattern and the high de novo rate.

PMID:24827800 SUPPORT Human Clinical

"Andersen - Tawil syndrome (ATS) is an autosomal - dominant or sporadic disorder characterized by ventricular arrhythmias, periodic paralysis, and distinctive facial and skeletal dysmorphism."

Independent review confirms autosomal dominant or sporadic inheritance alongside the defining triad.

PMID:20301441 SUPPORT Human Clinical

"Each child of an individual with ATS has a 50% chance of inheriting the disorder."

GeneReviews gives the per-child transmission risk used in genetic counseling of an affected parent.

+ 1 more reference

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Mechanistic Hypotheses

1

Single-Channel Three-Tissue Divergence Model

single_channel_three_tissue_divergence CANONICAL

Evidence balance 2 support

One Kir2.1 loss-of-function lesion produces three clinically unrelated manifestations because the same channel serves three distinct roles in three tissues: terminal repolarization and resting potential in cardiomyocytes and Purkinje fibers (yielding ventricular ectopy and bidirectional ventricular tachycardia); resting potential and excitability in skeletal myofibers (yielding potassium-sensitive periodic paralysis); and bioelectric patterning of the anterior ectoderm during neurulation (yielding craniofacial and skeletal dysmorphism). The cardiac and skeletal-muscle arms are excitability phenomena; the developmental arm is a non-excitable, voltage-mediated morphogenetic phenomenon.

Show evidence (2 references)

PMID:11371347 SUPPORT Human Clinical

"These findings suggest that Kir2.1 plays an important role in developmental signaling in addition to its previously recognized function in controlling cell excitability in skeletal muscle and heart."

The founding paper explicitly frames the divergence: one channel with an excitability role in heart and skeletal muscle plus a separate developmental-signalling role.

PMID:24383070 SUPPORT Human Clinical

"The loss-of-function mutations in KCNJ2 in ATS1 affect the excitability of both skeletal and cardiac muscle, which underlies the cardiac arrhythmias and periodic paralysis associated with ATS. Thus far, the molecular mechanism of the dysmorphic features is only poorly understood."

Confirms the two excitability arms and flags the developmental arm as the least understood branch of the divergence.

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Discussions and Knowledge Gaps

2

Is the craniofacial and skeletal dysmorphism of Andersen-Tawil syndrome caused by loss of Kir2.1-dependent bioelectric patterning of the anterior ectoderm during human neurulation, as demonstrated in Xenopus, and does the same voltage-mediated mechanism operate in human cranial neural crest and placode lineages?

HUMAN MODEL MISMATCH OPEN gap_ats_developmental_mechanism_in_human

Attached to

pathophysiology#Disrupted Bioelectric Craniofacial Patterning

The bioelectric mechanism for ATS dysmorphism is established in Xenopus laevis by misexpression of human ATS-associated KCNJ2 variants, optogenetic voltage manipulation, and rescue with unrelated ion translocators. No equivalent human tissue experiment exists, and human review literature continues to describe the dysmorphism mechanism as poorly understood. The mismatch matters because the frog work predicts a narrow, early neurula critical window and therefore a specific (and otherwise implausible) therapeutic opportunity for ion-flux-modifying drugs, a prediction that cannot be acted on without human-relevant confirmation.

Proposed experiments

Voltage and patterning-gene readout in human ATS cranial neural crest

exp_ats_human_ncc_voltage_patterning

Measure resting membrane potential regionalization and craniofacial patterning gene expression in human iPSC-derived cranial neural crest and placodal ectoderm carrying ATS KCNJ2 variants versus isogenic corrected controls.

Human anterior-ectoderm KCNJ2 expression atlas query

exp_ats_human_kcnj2_ectoderm_expression

Determine whether human KCNJ2 is expressed in the anterior ectoderm at the human developmental stage corresponding to the Xenopus neurula critical window, using human embryonic single-cell atlases.

Pharmacological voltage-normalization rescue in mutant human neural crest organoids

exp_ats_voltage_rescue_organoid

Test whether pharmacological normalization of membrane voltage in KCNJ2-mutant human neural crest organoids restores the disrupted craniofacial patterning gene expression domains.

Is flecainide safe and effective across Andersen-Tawil syndrome type 1, or is its effect variant-specific, with some Kir2.1 variants converting a class-Ic antiarrhythmic into a proarrhythmic agent?

KNOWLEDGE GAP OPEN gap_ats_flecainide_variant_specific_safety

Attached to

pathophysiology#Delayed Terminal Repolarization and Triggered Activity

Flecainide is widely used in ATS1 and is endorsed empirically by GeneReviews, yet a 2024 preprint reported that only 23% of reviewed patients had a genuine arrhythmia reduction, 13.5% suffered non-fatal cardiac arrest, and mouse and patient-derived iPSC models showed variant-dependent proarrhythmia. If confirmed, therapy selection in ATS would need to be genotype-stratified rather than uniform. The evidence is currently preprint-level and requires peer-reviewed replication.

Proposed experiments

Prospective genotype-stratified antiarrhythmic registry in ATS1

exp_ats_genotype_stratified_aad_registry

Conduct a prospective, genotype-stratified registry of antiarrhythmic response and adverse events in ATS1, powered to compare trafficking-defective versus gating-defective Kir2.1 variants.

Flecainide effect panel across ATS1 patient-derived iPSC cardiomyocyte lines

exp_ats_ipsc_flecainide_panel

Systematically measure the effect of flecainide on IK1 and INa across a panel of patient-derived iPSC cardiomyocyte lines representing the common ATS1 variant classes.

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Pathophysiology

9

KCNJ2 Loss-of-Function Variant

A germline, usually heterozygous loss-of-function variant in KCNJ2 alters the Kir2.1 strong inward-rectifier potassium channel. Reported mechanisms include defective trafficking of the channel to the surface membrane, altered gating, misfolding, and weakened coupling to PIP2. This is the upstream trigger of the entire ATS phenotype, and it is the ATS-specific substitution into the generic channelopathy module trigger node.

KCNJ2 hgnc:6263

inward rectifier potassium channel activity GO:0005242 ↓ DECREASED

Downstream

Dominant-Negative Kir2.1 Tetramer Dysfunction Mutant subunits are transcribed and translated and coassemble with wild-type subunits into the obligate Kir2.1 tetramer.

Show evidence (2 references)

PMID:11371347 SUPPORT Human Clinical

"We have mapped an Andersen's locus to chromosome 17q23 near the inward rectifying potassium channel gene KCNJ2."

Establishes KCNJ2 as the mapped ATS locus, the upstream trigger of the mechanism chain.

PMID:21148745 SUPPORT In Vitro

"Immunocytochemical analysis indicates that impaired trafficking of R260P-KCNJ2 channels."

Demonstrates defective surface trafficking as one route to Kir2.1 loss of function.

Dominant-Negative Kir2.1 Tetramer Dysfunction

Kir2.1 functions as a homotetramer, so mutant and wild-type subunits coassemble into mixed channels. A single mutant subunit can poison the tetramer, so current falls far below the 50% predicted by haploinsufficiency. This dominant-negative amplification explains both the autosomal dominant inheritance and the severity of the current deficit, and it is the single molecular lesion from which the three tissue-specific arms of the disease diverge.

potassium ion transmembrane transport GO:0071805 ↓ DECREASED

inward rectifier potassium channel activity GO:0005242 ↓ DECREASED

Downstream

Reduced Cardiac Inward Rectifier Current Kir2.1 is the principal carrier of cardiac IK1 in working ventricular myocardium and Purkinje fibres, so tetramer dysfunction lowers IK1.

Reduced Skeletal Muscle Inward Rectifier Current The same channel sets resting potential in skeletal myofibers, so the identical lesion produces a parallel current deficit in muscle.

Disrupted Bioelectric Craniofacial Patterning Beyond excitable tissue, Kir2.1-dependent potassium flux patterns resting membrane voltage in the anterior ectoderm during early neurulation.

Learning Difficulties A distinct neurocognitive phenotype accompanies the classic triad. The intermediate steps linking Kir2.1 loss to executive-function and abstract-reasoning deficits are not established.

Show evidence (3 references)

PMID:11371347 SUPPORT In Vitro

"Expression of two of these mutations in Xenopus oocytes revealed loss of function and a dominant negative effect in Kir2.1 current as assayed by voltage-clamp."

Direct voltage-clamp demonstration of the dominant-negative effect on Kir2.1 current.

PMID:21148745 SUPPORT In Vitro

"The R260P mutation produces a strong dominant negative effect leading to marked suppression of IK1 secondary to a trafficking defect."

Quantified dominant-negative suppression of IK1 by a heterozygously expressed ATS variant.

PMID:29018970 SUPPORT Model Organism

"AS has been directly linked to over 40 different autosomal dominant negative loss-of-function mutations in the KCNJ2 gene, encoding for the tetrameric strong inward rectifying K+ channel KIR2.1."

Confirms the tetrameric architecture that makes dominant-negative suppression possible.

Reduced Cardiac Inward Rectifier Current

Loss of Kir2.1 lowers the cardiac inward-rectifier current IK1. IK1 has two jobs in the ventricular myocyte: it clamps the phase-4 resting membrane potential near the potassium equilibrium potential, and its strong inward rectification means it supplies most of the repolarizing current in the terminal (phase 3) portion of the action potential while contributing almost nothing during the plateau. Reducing it therefore destabilizes the resting potential and prolongs terminal repolarization, which is registered on the surface electrocardiogram as a prolonged QU interval with prominent U waves rather than as marked QTc prolongation.

cardiomyocyte CL:0000746 cardiac Purkinje fibre cell CL:0002068

membrane repolarization during cardiac muscle cell action potential GO:0086013 ↓ DECREASED regulation of membrane potential GO:0042391 ↕ DYSREGULATED

Downstream

Delayed Terminal Repolarization and Triggered Activity Loss of terminal repolarizing current prolongs late phase 3 and leaves the myocyte vulnerable to afterdepolarization-driven triggered beats.

Show evidence (2 references)

PMID:38528561 SUPPORT In Vitro

"The spontaneous pulsation rate of myocardial cells in the mutation group was significantly lower than that in the repair CRISPR group, the action potential duration was prolonged, and the Kir2.1 current of the inward rectifier potassium ion channel was decreased, which is consistent with the..."

Isogenic CRISPR-corrected patient iPSC cardiomyocytes show reduced Kir2.1 current and prolonged action potential duration, tying the KCNJ2 variant causally to the cardiac electrophysiologic defect.

PMID:32947483 SUPPORT Human Clinical

"Prolongation of the QU/QUc intervals and normal or minimally prolonged QT/QTc intervals with a tendency to ventricular arrhythmias are typical repolarization changes."

Establishes that the surface electrocardiographic signature is QU prolongation with a normal or near-normal QTc, the reason LQT7 is a misleading label for ATS.

Delayed Terminal Repolarization and Triggered Activity

With IK1 reduced, the late phase-3 repolarizing brake is weakened and the resting potential is less firmly clamped, so residual depolarizing drive (including sodium-calcium exchanger current responding to cytosolic calcium) more readily reaches threshold. The result is delayed afterdepolarizations and triggered beats arising at rest, which is why ATS produces heavy resting ventricular ectopy rather than the exercise-restricted arrhythmia of catecholaminergic polymorphic ventricular tachycardia. This is the ATS-specific instance of the arrhythmogenic substrate node of the cardiac channelopathy module, and it is the pharmacological target of the variant-specific flecainide debate.

cardiomyocyte CL:0000746

cardiac muscle cell action potential GO:0086001 ⚠ ABNORMAL

Downstream

Bidirectional and Polymorphic Ventricular Tachycardia Triggered beats arising on this substrate organize into bidirectional and polymorphic ventricular tachycardia.

Show evidence (2 references)

PMID:24827800 SUPPORT Human Clinical

"The presence of frequent PVCs at rest are helpful in distinguishing ATS from typical catecholaminergic polymorphic ventricular tachycardia (CPVT). In typical CPVT, rapid PMVT and BiVT usually manifest during or after exercising."

Supports triggered ectopy arising at rest as the ATS-specific character of the arrhythmogenic substrate, distinguishing it from CPVT.

PMID:39711719 SUPPORT Model Organism

"Kir2.1 mutations impacting the resting membrane potential and cellular excitability create a substrate for life-threatening arrhythmias, raising significant concern about using these drugs in some ATS1 patients."

Links the resting-potential/excitability defect explicitly to formation of an arrhythmogenic substrate in cardiac-specific ATS1 mouse models.

Bidirectional and Polymorphic Ventricular Tachycardia

The characteristic sustained rhythm of ATS is bidirectional ventricular tachycardia, a form of polymorphic ventricular tachycardia in which the QRS axis alternates beat to beat. Frequent premature ventricular contractions, couplets, and bigeminy are the far more common everyday manifestation. Torsade de pointes is comparatively rare in ATS despite the LQT7 label.

cardiomyocyte CL:0000746

Downstream

Ventricular Arrhythmia Ventricular electrical instability is the cardinal cardiac manifestation of the disease, spanning isolated ectopy through sustained tachyarrhythmia.

Bidirectional Ventricular Tachycardia The rhythm itself is the observed clinical phenotype.

Premature Ventricular Contractions Triggered ectopic beats are recorded as frequent premature ventricular contractions.

Prominent U Wave Delayed terminal repolarization from reduced IK1 is registered on the surface electrocardiogram as a prolonged QU interval with a prominent U wave.

Prolonged QT Interval QT prolongation is present in a subset and gave rise to the historical LQT7 designation, though QTc is often normal or only mildly prolonged.

Palpitations Frequent ectopy and runs of ventricular tachycardia are perceived as palpitations.

Arrhythmic Loss of Cardiac Output Sustained or rapid ventricular tachycardia abolishes effective cardiac output.

Show evidence (2 references)

PMID:32947483 SUPPORT Human Clinical

"Bidirectional ventricular tachycardia is the hallmark ventricular arrhythmia, but also premature ventricular contractions, and rarely, polymorphic ventricular tachycardia of torsade de pointes type may be present."

Identifies bidirectional ventricular tachycardia as the hallmark ATS rhythm.

PMID:21148745 SUPPORT Human Clinical

"Our proband displayed dysmorphic features including micrognathia, clinodactyly, and syndactyly and exhibited multiform extrasystoles and bidirectional ventricular tachycardia both at rest and during exercise testing."

Case-level demonstration of bidirectional ventricular tachycardia present at rest as well as with exercise in a molecularly confirmed ATS patient.

Arrhythmic Loss of Cardiac Output

When a ventricular tachyarrhythmia is sustained or degenerates, cardiac output falls and cerebral perfusion is lost, producing syncope and, if the rhythm does not terminate, sudden cardiac death. Life-threatening events are far less common in ATS than the ectopic burden would suggest, but they do occur and are the reason for rhythm surveillance and, in selected patients, defibrillator implantation.

Downstream

Syncope Transient arrhythmia-induced cerebral hypoperfusion causes syncope.

Sudden Cardiac Death A ventricular tachyarrhythmia that does not terminate causes sudden cardiac death.

Show evidence (2 references)

PMID:24861851 SUPPORT Human Clinical

"KCNJ2 mutations cause a variable phenotype, with dysmorphic features seen in all patients studied, a high penetrance of periodic paralysis in males and ventricular arrhythmia with a risk of sudden cardiac death."

Establishes sudden cardiac death as a real risk of the ATS ventricular arrhythmia.

PMID:24861851 SUPPORT Human Clinical

"Two patients (with T75M and T309I mutations) had aborted sudden cardiac death. An implantable cardioverter-defibrillator was utilized in 40% of cases."

Documents aborted sudden cardiac death events and defibrillator use in a molecularly defined ATS cohort.

Reduced Skeletal Muscle Inward Rectifier Current

The second arm of the divergence. Kir2.1 is also the dominant inward-rectifier channel of the skeletal myofiber sarcolemma and transverse tubules, where it holds the resting membrane potential near the potassium equilibrium potential. Myotubes cultured from ATS patients lack the inwardly rectifying barium-sensitive current entirely, and their resting potential shifts in the depolarizing direction. Importantly, ATS myoblasts show no morphological, proliferative, or fusion defect, so the muscle phenotype is electrical rather than dystrophic.

skeletal muscle fiber CL:0008002

regulation of membrane potential GO:0042391 ↕ DYSREGULATED potassium ion transmembrane transport GO:0071805 ↓ DECREASED

Downstream

Paradoxical Sarcolemmal Depolarization and Inexcitability With the resting potential no longer clamped, potassium shifts drive the fiber into sustained depolarization instead of restoring excitability.

Show evidence (2 references)

PMID:19570891 SUPPORT In Vitro

"Current recordings carried out on myotubes revealed the absence of an inwardly rectifying Ba2+-sensitive current in affected patient cells. One consequence of the Ik1 current loss in Andersen's syndrome myotubes is a shift of the resting membrane potential toward depolarizing potentials."

Ex vivo human patient myotubes show loss of the inward rectifier current and consequent depolarization of the resting membrane potential.

PMID:29018970 SUPPORT Model Organism

"Whole-cell voltage-clamp recordings in individual skeletal muscle fibers confirmed the reduction of inwardly rectifying K+ current (IK1) after transduction with ∆314-315 KIR2.1 as compared to WT channels."

In vivo mouse confirmation that an ATS variant reduces skeletal muscle IK1.

Paradoxical Sarcolemmal Depolarization and Inexcitability

Normally, a fall or rise in extracellular potassium is buffered by the strong inward rectifier, which holds resting potential near the potassium equilibrium potential. With Kir2.1 lost, that buffering fails and the fiber depolarizes paradoxically during potassium shifts. Sustained depolarization inactivates the voltage-gated sodium channels and the fiber becomes electrically inexcitable despite being structurally intact, producing flaccid weakness that resolves as the potassium disturbance corrects. This is why attacks in ATS may be hypokalaemic, hyperkalaemic, or normokalaemic: the defect is the loss of buffering, not a fixed direction of potassium sensitivity.

skeletal muscle fiber CL:0008002

skeletal muscle contraction GO:0003009 ↓ DECREASED

Downstream

Periodic Paralysis Episodic fiber inexcitability presents clinically as periodic paralysis.

Episodic Flaccid Weakness Loss of fiber excitability produces flaccid rather than spastic weakness, with preserved muscle structure between attacks.

Muscle Weakness Repeated or persistent electrical dysfunction contributes to mild fixed interictal weakness in many affected individuals.

Show evidence (3 references)

PMID:17395133 SUPPORT Human Clinical

"The skeletal muscle and cardiac symptoms are accounted for, in most cases, by a dominant negative effect of the mutations on potassium channel current, resulting in prolonged depolarization of the action potential."

States the prolonged-depolarization mechanism shared by the cardiac and skeletal-muscle arms of the disease.

PMID:29018970 SUPPORT Model Organism

"Analysis of skeletal muscle function revealed reduced force generation during isometric contraction as well as reduced resistance to muscle fatigue in extensor digitorum longus muscles transduced with AS mutant KIR2.1."

Demonstrates that the IK1 deficit translates into a measurable contractile-function deficit in intact muscle.

PMID:24861851 SUPPORT Human Clinical

"All patients had dysmorphic features; periodic paralysis affected males more frequently than females (80% vs. 20%), and most attacks were normokalemic."

Supports the observation that ATS attacks are not fixed to one direction of potassium disturbance and are frequently normokalaemic.

Disrupted Bioelectric Craniofacial Patterning

The third arm of the divergence, and the least understood. Beyond its role in excitable tissue, Kir2.1-dependent potassium flux establishes a regionalized pattern of resting membrane potential across the anterior ectoderm during early neurulation. This voltage pattern acts as a morphogenetic instruction: in Xenopus, misexpressing human ATS-associated KCNJ2 variants disrupts the voltage map, derails ten craniofacial patterning genes including cranial neural crest and placode markers, and produces craniofacial anomalies in the same structures affected in humans. Critically, the effect is voltage-specific rather than channel-specific: unrelated ion translocators that change membrane voltage reproduce the anomalies, whereas electroneutral or inactive channels do not. The resulting malformations are developmental and fixed, unlike the episodic cardiac and muscular manifestations.

migratory cranial neural crest cell CL:0000333

regulation of membrane potential GO:0042391 ↕ DYSREGULATED embryonic cranial skeleton morphogenesis GO:0048701 ⚠ ABNORMAL

Downstream

Low-Set Ears Disrupted arch and placode-derived patterning affects external ear position.

Hypertelorism Altered midfacial patterning widens interorbital spacing.

Micrognathia Disrupted mandibular arch patterning produces a small or receding mandible.

Broad Forehead Altered anterior ectodermal patterning produces a broad forehead.

Clinodactyly of the 5th Finger Kir2.1-dependent bioelectric patterning also operates in limb development, producing incurving of the fifth digit.

Syndactyly Digit separation is incomplete, most often affecting the toes.

Short Stature Skeletal growth is reduced as part of the developmental phenotype.

Scoliosis Axial skeletal patterning is affected, producing scoliosis.

Show evidence (3 references)

PMID:26864374 SUPPORT Model Organism

"Misexpression in Xenopus of KCNJ2 carrying ATS-associated mutations causes CFAs in the same structures affected in humans, changes the normal pattern of membrane voltage potential regionalization in the developing face and disrupts expression of important craniofacial patterning genes, revealing..."

Provides the mechanistic model for the developmental arm: human ATS KCNJ2 variants disrupt the ectodermal voltage map and craniofacial patterning gene expression in Xenopus.

PMID:26864374 SUPPORT Model Organism

"We predict that the critical time is early during neurulation, and the critical cells are the ectodermal cranial neural crest and placode lineages."

Identifies the neurula-stage critical window and the cranial neural crest and placode lineages.

PMID:24383070 PARTIAL Human Clinical

"Thus far, the molecular mechanism of the dysmorphic features is only poorly understood."

Human review literature explicitly flags the developmental arm as incompletely understood, which is why the Xenopus evidence is carried with an accompanying HUMAN_MODEL_MISMATCH discussion.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

22

Cardiovascular 5

Ventricular Arrhythmia FREQUENT Ventricular arrhythmia HP:0004308

Show evidence (1 reference)

PMID:32947483 SUPPORT Human Clinical

"About 60% of affected individuals have all features of the major triad."

Supports FREQUENT (30-79%) for the triad components: about 60% of affected individuals manifest all three, so each component is at least that common.

Prolonged QT Interval Prolonged QT interval HP:0001657

Show evidence (2 references)

PMID:20301441 SUPPORT Human Clinical

"ventricular arrhythmias and prolonged QT interval"

GeneReviews lists prolonged QT interval as part of the defining ATS triad.

PMID:24383070 SUPPORT Human Clinical

"ATS patients may show a prolongation of the QT interval,which explains the classification as long QT syndrome type 7 (LQT7), and specific neurological or neurocognitive defects."

Explains the origin of the LQT7 classification while noting QT prolongation is only sometimes present.

Palpitations Palpitations HP:0001962

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"Affected individuals present in the first or second decade with either cardiac symptoms (palpitations and/or syncope) or weakness that occurs spontaneously following prolonged rest or following rest after exertion."

GeneReviews names palpitations as a common presenting cardiac symptom.

Syncope Syncope HP:0001279

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"Affected individuals present in the first or second decade with either cardiac symptoms (palpitations and/or syncope) or weakness that occurs spontaneously following prolonged rest or following rest after exertion."

GeneReviews names syncope as a presenting cardiac symptom of ATS.

Sudden Cardiac Death Sudden cardiac death HP:0001645

Show evidence (1 reference)

PMID:24861851 SUPPORT Human Clinical

"Two patients (with T75M and T309I mutations) had aborted sudden cardiac death. An implantable cardioverter-defibrillator was utilized in 40% of cases."

Documents aborted sudden cardiac death in a molecularly confirmed ATS cohort.

Ear 1

Low-Set Ears Low-set ears HP:0000369

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"

GeneReviews lists low-set ears among the defining ATS anomalies.

Eye 1

Hypertelorism Hypertelorism HP:0000316

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"

GeneReviews lists widely spaced eyes (hypertelorism) among the defining ATS anomalies.

Head and Neck 1

Micrognathia Micrognathia HP:0000347

An earlier draft of this entry additionally asserted that micrognathia is a risk marker for life-threatening arrhythmic events in ATS. That claim was removed because no cited source supports it: the largest ATS1 outcome cohort (PMID:32299589, 118 patients from 57 families) identifies a history of syncope, documented sustained ventricular tachycardia, and amiodarone administration as the predictors of life-threatening arrhythmic events, and does not report any dysmorphic feature among them. Those evidenced predictors are recorded in the progression section instead.

Show evidence (2 references)

PMID:20301441 SUPPORT Human Clinical

"anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"

GeneReviews lists a small mandible among the defining ATS anomalies.

PMID:21148745 SUPPORT Human Clinical

"Our proband displayed dysmorphic features including micrognathia, clinodactyly, and syndactyly"

Case-level documentation of micrognathia in a molecularly confirmed ATS patient.

Limbs 1

Syndactyly Syndactyly HP:0001159

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"

GeneReviews lists syndactyly among the defining ATS anomalies.

Metabolism 2

Hypokalemia Hypokalemia HP:0002900

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"For episodic weakness: if serum potassium concentration is low (<3.0 mmol/L), administration of oral potassium"

GeneReviews management guidance presupposes hypokalaemic attacks in ATS.

Hyperkalemia Hyperkalemia HP:0002153

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"if serum potassium concentration is high, ingesting carbohydrates may lower serum potassium levels"

GeneReviews gives specific management for the hyperkalaemic attack, establishing that ATS attacks occur with high potassium as well as low.

Musculoskeletal 2

Muscle Weakness Muscle weakness HP:0001324

Show evidence (2 references)

PMID:20301441 SUPPORT Human Clinical

"Mild permanent weakness is common."

GeneReviews documents mild fixed interictal weakness as a common feature.

PMID:19570891 SUPPORT Human Clinical

"Muscle weakness has been reported in two-thirds of the patients."

Quantifies the frequency of muscle weakness in reported ATS patients.

Scoliosis Scoliosis HP:0002650

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"

GeneReviews lists scoliosis among the defining ATS anomalies.

Growth 1

Short Stature Short stature HP:0004322

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"

GeneReviews lists short stature among the defining ATS anomalies.

Other 8

Bidirectional Ventricular Tachycardia Bidirectional ventricular tachycardia HP:0034040

Show evidence (2 references)

PMID:32947483 SUPPORT Human Clinical

"Bidirectional ventricular tachycardia is the hallmark ventricular arrhythmia, but also premature ventricular contractions, and rarely, polymorphic ventricular tachycardia of torsade de pointes type may be present."

Identifies bidirectional ventricular tachycardia as the hallmark ATS arrhythmia.

PMID:24827800 SUPPORT Human Clinical

"Cardiac manifestations of ATS include frequent premature ventricular contractions (PVC), Q-U interval prolongation, prominent U-waves, and a special type of polymorphic ventricular tachycardia (PMVT) called bidirectional ventricular tachycardia (BiVT)."

Independent confirmation of bidirectional ventricular tachycardia as a core cardiac manifestation.

Premature Ventricular Contractions Premature ventricular contraction HP:0006682

Show evidence (1 reference)

PMID:24827800 SUPPORT Human Clinical

"PVCs at rest are quite frequent in ATS1 patients, however, in LQTS patients, PVCs and asymptomatic VT are uncommon which also contributes to differentiating them."

Documents frequent resting premature ventricular contractions as a characteristic and discriminating ATS finding.

Prominent U Wave Prominent U wave HP:0025072

Show evidence (1 reference)

PMID:32947483 SUPPORT Human Clinical

"Prolongation of the QU/QUc intervals and normal or minimally prolonged QT/QTc intervals with a tendency to ventricular arrhythmias are typical repolarization changes."

Establishes prolonged QU with a normal or minimally prolonged QT as the typical ATS repolarization signature.

Periodic Paralysis FREQUENT Periodic paralysis HP:0003768

Show evidence (2 references)

PMID:20301441 SUPPORT Human Clinical

"Affected individuals present in the first or second decade with either cardiac symptoms (palpitations and/or syncope) or weakness that occurs spontaneously following prolonged rest or following rest after exertion."

GeneReviews describes the characteristic triggers of the weakness attacks.

PMID:32947483 SUPPORT Human Clinical

"About 60% of affected individuals have all features of the major triad."

Supports FREQUENT (30-79%) for the triad components: about 60% of affected individuals manifest all three.

Episodic Flaccid Weakness Episodic flaccid weakness HP:0003752

Show evidence (1 reference)

PMID:32947483 SUPPORT Human Clinical

"The typical muscular change is episodic flaccid muscle weakness."

Directly states the flaccid, episodic character of the weakness.

Broad Forehead Broad forehead HP:0000337

Show evidence (1 reference)

PMID:32947483 PARTIAL Human Clinical

"Patients with ATS have characteristic physical developmental dysmorphisms that affect the face, skull, limbs, thorax, and stature."

Supports the presence of characteristic facial and skull dysmorphism. Marked PARTIAL because the abstract does not enumerate broad forehead specifically; the specific feature is drawn from the wider ATS literature.

Clinodactyly of the 5th Finger Clinodactyly of the 5th finger HP:0004209

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"

GeneReviews lists fifth-digit clinodactyly among the defining ATS anomalies.

Learning Difficulties Specific learning disability HP:0001328

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"Mild learning difficulties and a distinct neurocognitive phenotype (i.e., deficits in executive function and abstract reasoning) have been described."

GeneReviews documents the neurocognitive phenotype of ATS.

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Genetic Associations

3

KCNJ2

Gene: KCNJ2 hgnc:6263 relationship_type: CAUSATIVE

Show evidence (3 references)

PMID:11371347 SUPPORT Human Clinical

"A missense mutation in KCNJ2 (encoding D71V) was identified in the linked family. Eight additional mutations were identified in unrelated patients."

The original linkage and mutation-identification study establishing KCNJ2 as the ATS gene.

PMID:24827800 SUPPORT Human Clinical

"KCNJ2 mutations are detectable in up to 60 % of patients with ATS."

Quantifies the diagnostic yield of KCNJ2 testing in clinically diagnosed ATS.

PMID:17395133 SUPPORT Human Clinical

"Mechanisms of disruption of channel function include abnormal trafficking and assembly of second messengers such as phosphatidylinositol 4,5-bisphosphate, abnormal gating of the channel, and incorrect folding of the Kir2.1 protein."

Enumerates the molecular routes by which KCNJ2 variants produce Kir2.1 loss of function.

KCNJ5

Gene: KCNJ5 hgnc:6266 relationship_type: CAUSATIVE

Show evidence (1 reference)

PMID:32947483 PARTIAL Human Clinical

"ATS type 2 is in turn linked to a rare mutation in the KCNJ5-GIRK4 gene that encodes the G protein-sensitive-activated inwardly rectifying K+ channel Kir3.4 (15%), which carries the acetylcholine-induced potassium current."

Review attributes a minority of ATS to KCNJ5. Marked PARTIAL because this assignment is not consistently replicated; other reviews describe KCNJ2-negative ATS as genetically unresolved rather than KCNJ5-related.

Genetically unsolved ATS

relationship_type: UNKNOWN

Show evidence (2 references)

PMID:24383070 SUPPORT Human Clinical

"In ATS type 2 (ATS2), which does not differ from ATS1 in its clinical symptoms, the genetic defect is unknown."

Establishes that ATS2 is a genetically unresolved residue category, clinically identical to ATS1.

PMID:32947483 SUPPORT Human Clinical

"About 30% of cases are de novo/sporadic, suggesting that additional as-yet unidentified genes also cause the disorder."

Supports the existence of additional, currently unidentified ATS loci.

💊

Medical Actions

7

Oral Potassium Repletion for Hypokalaemic Attacks

Action: oral potassium repletion Ontology label: Pharmacotherapy NCIT:C15986

Agent: potassium chloride CHEBI:32588

For a paralytic attack occurring with documented hypokalaemia, oral potassium is given until the serum concentration normalizes. Potassium must be measured before repletion and cardiac monitoring obtained where possible, because ATS attacks may also be normokalaemic or hyperkalaemic and blanket supplementation would then be unsafe. If serum potassium is high, ingesting carbohydrates instead lowers it.

Mechanism Target:

INHIBITS Paradoxical Sarcolemmal Depolarization and Inexcitability — Correcting the potassium disturbance restores the driving force that the unbuffered sarcolemma can no longer maintain, allowing the fiber to repolarize and regain excitability.

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"For episodic weakness: if serum potassium concentration is low (<3.0 mmol/L), administration of oral potassium (20-30 mEq/L) every 15-30 minutes (not to exceed 200 mEq in a 12-hour period) until the serum concentration normalizes"

GeneReviews gives the specific potassium repletion protocol for hypokalaemic ATS attacks.

Carbonic Anhydrase Inhibitor Prophylaxis

Action: carbonic anhydrase inhibitor prophylaxis Ontology label: Pharmacotherapy NCIT:C15986

Agent: acetazolamide CHEBI:27690

Carbonic anhydrase inhibitors such as acetazolamide, together with daily slow-release potassium supplementation and trigger avoidance, are used to reduce the frequency and severity of paralytic attacks. The evidence in ATS specifically is limited and largely extrapolated from the other periodic paralyses, and electrolyte and renal effects require monitoring.

Mechanism Target:

INHIBITS Paradoxical Sarcolemmal Depolarization and Inexcitability — Prophylaxis is directed at reducing the frequency with which potassium shifts drive the unbuffered sarcolemma into inexcitability.

Show evidence (1 reference)

PMID:20301441 SUPPORT Human Clinical

"Reduction in frequency and severity of episodic attacks of weakness with lifestyle/dietary modification to avoid known triggers; use of carbonic anhydrase inhibitors; daily use of slow-release potassium supplements"

GeneReviews recommends carbonic anhydrase inhibitors and slow-release potassium for attack prophylaxis.

Flecainide

Action: flecainide therapy Ontology label: Pharmacotherapy NCIT:C15986

Agent: flecainide CHEBI:75984

Flecainide is used empirically for significant, frequent ventricular arrhythmia in ATS and has suppressed bidirectional ventricular tachycardia where beta-blockade failed. Its safety is now under active reassessment: a 2024 preprint reviewing 53 ATS1 patients found genuine arrhythmia reduction in only 23%, non-fatal cardiac arrest in 13.5%, and variant-dependent proarrhythmia in mouse and patient-derived iPSC models, concluding that class-Ic drugs may be proarrhythmic in some ATS1 patients. Separately, GeneReviews cautions that class I antiarrhythmics may paradoxically worsen the neuromuscular symptoms, so flecainide is a drug whose benefit must be weighed against two distinct hazards.

Mechanism Target:

INHIBITS Delayed Terminal Repolarization and Triggered Activity — Flecainide suppresses the triggered ectopic activity arising on the IK1-depleted substrate, although its net effect is variant-dependent and may be proarrhythmic for some Kir2.1 variants.

Show evidence (5 references)

PMID:20301441 SUPPORT Human Clinical

"Empiric treatment with flecainide should be considered for significant, frequent ventricular arrhythmias in the setting of reduced left ventricular function."

GeneReviews endorses empiric flecainide for significant ventricular arrhythmia in ATS.

PMID:21148745 SUPPORT Human Clinical

"The patient's symptoms continued after administration of nadolol but subsided after treatment with flecainide."

Case-level evidence of flecainide efficacy where beta-blockade failed.

PMID:39711719 PARTIAL Human Clinical

"Of 53 ATS1 patients reviewed from the literature, 54% responded partially to flecainide, with ventricular arrhythmia (VA) reduction in only 23%."

Tempers the efficacy claim. Marked PARTIAL because this literature review shows only a minority achieve genuine arrhythmia reduction, and the source is a preprint awaiting peer review.

+ 2 more references

Beta-Blocker Therapy

Action: Pharmacotherapy NCIT:C15986

Agent: beta-adrenergic antagonist NCIT:C29576

Beta-adrenergic blockade is widely used in inherited arrhythmia syndromes and is frequently prescribed in ATS on the rationale that suppressing adrenergic drive limits triggered activity. In the largest ATS1 outcome cohort, however, beta-blockers alone did not reduce the rate of life-threatening arrhythmic events relative to no therapy, nor did they in combination with class Ic antiarrhythmic drugs. Beta-blockade is therefore recorded here as a commonly used but unproven strategy in ATS rather than as an established disease-modifying therapy, and it is the comparator arm under formal test in the ongoing N-of-1 trial series NCT06205550.

Mechanism Target:

INHIBITS Delayed Terminal Repolarization and Triggered Activity — The intended mechanism is reduction of adrenergic facilitation of delayed afterdepolarization-driven triggered activity. Outcome data do not show a corresponding reduction in life-threatening arrhythmic events, so the mechanistic rationale should not be read as demonstrated clinical benefit.

Show evidence (2 references)

PMID:32299589 REFUTE Human Clinical

"was not reduced by beta-blockers alone (1.37 per 100 py; p = 1.00), or in combination with Class Ic antiarrhythmic drugs (1.46 per 100 py, p = 1.00)."

Refutes an event-reducing effect of beta-blockade, alone or added to class Ic therapy, in the largest reported ATS1 outcome cohort.

clinicaltrials:NCT06205550 PARTIAL Human Clinical

"For ATS, flecainide monotherapy will be compared with combination therapy of flecainide and a β-blocker or calcium channel blocker."

Documents that beta-blocker add-on to flecainide remains an open question being tested prospectively rather than an established standard.

Implantable Cardioverter-Defibrillator

Action: implantable cardioverter-defibrillator implantation Ontology label: Surgical Procedure NCIT:C15329

An implantable cardioverter-defibrillator is used for survivors of cardiac arrest, for tachycardia-induced syncope, and for selected patients with recurrent haemodynamically significant sustained ventricular tachycardia despite medical therapy. Frequent but tolerated ectopy alone does not warrant implantation.

Mechanism Target:

INHIBITS Arrhythmic Loss of Cardiac Output — The device does not modify the substrate; it terminates a haemodynamically catastrophic rhythm before it becomes fatal.

Show evidence (2 references)

PMID:20301441 SUPPORT Human Clinical

"implantable cardioverter-defibrillator for those with tachycardia-induced syncope"

GeneReviews gives the indication for defibrillator implantation in ATS.

PMID:24861851 SUPPORT Human Clinical

"An implantable cardioverter-defibrillator was utilized in 40% of cases."

Documents real-world defibrillator use in a molecularly confirmed ATS cohort.

Avoidance of QT-Prolonging and Potassium-Wasting Agents

Action: avoidance of contraindicated medications Ontology label: Supportive Care NCIT:C15747

ATS carries specific drug-safety warnings. Medications known to prolong the QT interval should be avoided; salbutamol inhalers may exacerbate cardiac arrhythmias; and thiazide and other potassium-wasting diuretics may provoke drug-induced hypokalaemia, precipitating paralytic attacks and aggravating QT prolongation. Amiodarone deserves separate emphasis: in the largest ATS1 outcome cohort its administration carried by far the strongest association with life-threatening arrhythmic events, and the authors conclude it is proarrhythmic and should be avoided. Because cardiac and skeletal muscle respond differently, a drug that helps one tissue may harm the other, which is the central management difficulty of the disorder.

Mechanism Target:

INHIBITS Delayed Terminal Repolarization and Triggered Activity — Removing QT-prolonging and potassium-wasting exposures prevents further loading of an already destabilized repolarization reserve.

Show evidence (3 references)

PMID:20301441 SUPPORT Human Clinical

"Agents/circumstances to avoid: Medications known to prolong QT intervals; salbutamol inhalers (may exacerbate cardiac arrhythmias); thiazide and other potassium-wasting diuretics (may provoke drug-induced hypokalemia and could aggravate the QT interval prolongation)."

The GeneReviews Agents/Circumstances to Avoid section, recorded verbatim as the drug-safety warning for ATS.

PMID:17395133 SUPPORT Human Clinical

"Because of differences in cardiac and skeletal muscle physiology, drugs that may have a beneficial effect on cardiac function may have a detrimental effect on skeletal muscle and vice versa."

States the cross-tissue therapeutic conflict that makes drug selection in ATS uniquely difficult.

PMID:32299589 SUPPORT Human Clinical

"Amiodarone is proarrhythmic and should be avoided in patients with ATS1."

Adds amiodarone to the ATS drug-avoidance list on the basis of cohort outcome data.

Rhythm Surveillance and Cascade Testing

Action: rhythm surveillance and cascade genetic testing Ontology label: Supportive Care NCIT:C15747

Asymptomatic individuals with a KCNJ2 pathogenic variant undergo annual 12-lead electrocardiography and 24-hour Holter monitoring. Relatives at risk are offered molecular testing if the familial variant is known, or detailed neurologic and cardiologic evaluation with electrocardiography and Holter monitoring if it is not.

Show evidence (2 references)

PMID:20301441 SUPPORT Human Clinical

"Surveillance: Annual screening of asymptomatic individuals with a KCNJ2 pathogenic variant with a 12-lead EKG and 24-hour Holter monitoring."

GeneReviews specifies the surveillance protocol for KCNJ2 variant carriers.

PMID:20301441 SUPPORT Human Clinical

"Evaluation of relatives at risk: Molecular genetic testing if the pathogenic variant is known; if not, detailed neurologic and cardiologic evaluation, 12-lead EKG, and 24-hour Holter monitoring to reduce morbidity and mortality through early diagnosis and treatment of at-risk relatives."

GeneReviews specifies cascade evaluation of at-risk relatives.

🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Andersen-Tawil Syndrome:

Catecholaminergic polymorphic ventricular tachycardia MONDO:0017990

Overlapping Features CPVT shares bidirectional ventricular tachycardia with ATS and is the principal arrhythmic mimic. The discriminator is the resting ectopy burden and the trigger context: frequent premature ventricular contractions at rest favour ATS, whereas CPVT arrhythmia is adrenergically driven and emerges during or after exercise.

Distinguishing Features

Frequent premature ventricular contractions at rest favour ATS over typical CPVT
In CPVT, polymorphic and bidirectional ventricular tachycardia are exercise- or catecholamine-provoked rather than present at rest
Periodic paralysis and the dysmorphic triad are absent in CPVT

Show evidence (2 references)

PMID:24827800 SUPPORT Human Clinical

"The presence of frequent PVCs at rest are helpful in distinguishing ATS from typical catecholaminergic polymorphic ventricular tachycardia (CPVT)."

States the resting-ectopy discriminator between ATS and CPVT.

PMID:24827800 SUPPORT Human Clinical

"In typical CPVT, rapid PMVT and BiVT usually manifest during or after exercising."

Establishes the exercise-provoked trigger context that separates CPVT from ATS.

Long QT syndrome MONDO:0002442

Overlapping Features ATS has historically been labelled LQT7, but the repolarization abnormality is QU rather than QT prolongation and the arrhythmia profile differs. Frequent resting premature ventricular contractions and asymptomatic ventricular tachycardia are characteristic of ATS and uncommon in long QT syndrome, whose torsade de pointes is faster and more often symptomatic.

Distinguishing Features

ATS prolongs QU/QUc with a normal or only minimally prolonged QT/QTc
Frequent resting premature ventricular contractions and asymptomatic ventricular tachycardia are typical of ATS but uncommon in LQTS
Periodic paralysis and the dysmorphic triad are absent in isolated LQTS

Show evidence (2 references)

PMID:24827800 SUPPORT Human Clinical

"PVCs at rest are quite frequent in ATS1 patients, however, in LQTS patients, PVCs and asymptomatic VT are uncommon which also contributes to differentiating them."

States the resting-ectopy discriminator between ATS1 and long QT syndrome.

PMID:32947483 SUPPORT Human Clinical

"Prolongation of the QU/QUc intervals and normal or minimally prolonged QT/QTc intervals with a tendency to ventricular arrhythmias are typical repolarization changes."

Supports the interval-based discriminator: ATS prolongs QU rather than QT, which is why the historical LQT7 label is misleading.

🔬

Clinical Trials

3

NCT00521794 NOT_APPLICABLE COMPLETED

Completed multi-site observational natural-history study (28 participants) characterizing ATS, establishing whether manifestations change over time, and testing whether they correlate with KCNJ2 genotype. This is the genotype-phenotype correlation study underlying much of the longitudinal ATS literature; it is observational, so no trial phase applies.

Target Phenotypes: Periodic paralysis HP:0003768 Ventricular arrhythmia HP:0004308

Show evidence (1 reference)

clinicaltrials:NCT00521794 SUPPORT Human Clinical

"The purpose of this multi-site study is to better characterize ATS, establish whether symptoms change over time, and determine if symptoms are related to a mutation in the KCNJ2 gene."

ClinicalTrials.gov documents a completed longitudinal genotype-phenotype study in ATS.

NCT00839501 PHASE_I TERMINATED

Interventional trial of potassium supplementation and acetazolamide, testing whether either affects the duration of episodic weakness and the cardiac rhythm abnormalities of ATS. Terminated in 2011 for inability to recruit a sufficient number of participants, so it produced no efficacy read-out. This is the reason the potassium-repletion and carbonic anhydrase inhibitor treatments in this entry rest on GeneReviews management guidance rather than on randomized evidence.

Target Phenotypes: Episodic flaccid weakness HP:0003752 Ventricular arrhythmia HP:0004308

Show evidence (2 references)

clinicaltrials:NCT00839501 SUPPORT Human Clinical

"The purpose of this study is to determine whether potassium supplements and/or the medication acetazolamide affect the duration of muscle weakness and heart rhythm abnormalities in people with ATS."

Documents the intended interventions and endpoints of the only registered therapeutic trial of the two mainstay ATS treatments.

clinicaltrials:NCT00839501 PARTIAL Human Clinical

"The cause of some ATS cases remains unknown, and no specific treatments have been established."

Supports the entry's position that ATS therapy is not established on randomized evidence; graded PARTIAL because it states the evidence gap rather than any treatment effect.

NCT06205550 PHASE_II NOT_RECRUITING

Aggregated series of randomized, open-label N-of-1 trials in adults with ATS or multifocal ectopic Purkinje-related premature contractions who are already on flecainide. For ATS, flecainide monotherapy is compared with flecainide plus a beta-blocker or calcium channel blocker, with ventricular ectopy burden on electrocardiographic monitoring as the primary endpoint. Its explicit rationale is the lack of high-quality efficacy evidence for the therapeutic strategies currently used, which is the same gap this entry records around flecainide and beta-blockade.

Target Phenotypes: Premature ventricular contractions HP:0006682 Bidirectional ventricular tachycardia HP:0034040

Show evidence (2 references)

clinicaltrials:NCT06205550 SUPPORT Human Clinical

"Objective: To investigate the efficacy of various therapeutic strategies for reducing ventricular ectopy burden in patients with ATS or MEPPC."

States the objective of the only currently registered interventional antiarrhythmic trial in ATS.

clinicaltrials:NCT06205550 SUPPORT Human Clinical

"A number of therapeutic strategies are suggested in these conditions, but there is a lack of high-quality evidence on their efficacy."

Documents the evidence gap that motivates the trial and that this entry records in its treatment grading.

{ }

Source YAML

click to show

name: Andersen-Tawil Syndrome
creation_date: '2026-07-31T00:00:00Z'
description: >-
  Andersen-Tawil syndrome (ATS) is a rare autosomal dominant multisystem
  channelopathy defined by a clinical triad of ventricular arrhythmia, periodic
  paralysis, and distinctive craniofacial and skeletal dysmorphic features.
  Roughly 50-60% of affected individuals carry a loss-of-function variant in
  KCNJ2, which encodes the strong inward-rectifier potassium channel Kir2.1
  (ATS type 1); a minority carry KCNJ5 (Kir3.4) variants, and a substantial
  fraction remain genetically unsolved (historically termed ATS type 2). ATS is
  historically catalogued as long QT syndrome type 7 (LQT7), but the label is
  misleading: QTc is often normal or only minimally prolonged, and the more
  characteristic electrocardiographic abnormality is a prolonged QU interval
  with prominent U waves, frequent premature ventricular contractions at rest,
  and bidirectional ventricular tachycardia. The entry's most distinctive
  feature is mechanistic: a single channel lesion diverges into three tissue
  compartments, because Kir2.1 sets resting membrane potential and terminal
  repolarization in cardiac muscle, sets resting potential and excitability in
  skeletal muscle, and patterns bioelectric state in the developing
  craniofacial ectoderm.
category: Genetic
disease_term:
  preferred_term: Andersen-Tawil syndrome
  term:
    id: MONDO:0008222
    label: Andersen-Tawil syndrome
synonyms:
- ATS
- Andersen syndrome
- Andersen cardiodysrhythmic periodic paralysis
- long QT syndrome 7
- LQT7
- potassium-sensitive periodic paralysis with ventricular dysrhythmia
parents:
- Cardiac Arrhythmia
- Channelopathy
classifications:
  harrisons_chapter:
  - classification_value: CARDIOVASCULAR
    evidence:
    - reference: PMID:24861851
      reference_title: "Andersen-Tawil syndrome: report of 3 novel mutations and high risk of symptomatic cardiac involvement."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Andersen-Tawil syndrome (ATS) is a potassium channelopathy affecting cardiac and skeletal muscle."
      explanation: >-
        The cardiac arm of the channelopathy (ventricular arrhythmia, QU
        prolongation, sudden cardiac death) places ATS in the cardiovascular
        Part alongside the other inherited arrhythmia syndromes.
  - classification_value: NEUROLOGIC
    evidence:
    - reference: PMID:24861851
      reference_title: "Andersen-Tawil syndrome: report of 3 novel mutations and high risk of symptomatic cardiac involvement."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Andersen-Tawil syndrome (ATS) is a potassium channelopathy affecting cardiac and skeletal muscle."
      explanation: >-
        The skeletal-muscle arm is a primary periodic paralysis, a neuromuscular
        disorder, so ATS is also assigned to the neurologic Part.
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    evidence:
    - reference: PMID:20301441
      reference_title: "Andersen-Tawil Syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "ATS is inherited in an autosomal dominant manner."
      explanation: >-
        ATS is a Mendelian single-gene disorder, so it also belongs to the
        genetics Part.
  channelopathy_category:
    classification_value: cardiac channelopathy
    notes: >-
      ATS is a mixed cardiac and skeletal-muscle inward-rectifier
      channelopathy: the same Kir2.1 loss of function reduces IK1 in both
      tissues. ChannelopathyOrganSystemEnum is single-valued in the schema, so
      only the cardiac assignment can be recorded here; the skeletal-muscle
      channelopathy arm is modeled explicitly in the pathophysiology nodes
      "Reduced Skeletal Muscle Inward Rectifier Current" and "Paradoxical
      Sarcolemmal Depolarization and Inexcitability". The cardiac value is
      chosen because it is the arm that carries the mortality risk and the
      reason this entry joins the Inherited_Arrhythmia_Syndromes grouping.
    evidence:
    - reference: PMID:24861851
      reference_title: "Andersen-Tawil syndrome: report of 3 novel mutations and high risk of symptomatic cardiac involvement."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "Andersen-Tawil syndrome (ATS) is a potassium channelopathy affecting cardiac and skeletal muscle."
      explanation: >-
        Supports the potassium-channelopathy classification and its cardiac
        involvement; graded PARTIAL because the source explicitly names both
        cardiac and skeletal muscle while this single-valued slot can only
        record the cardiac assignment.
notes: >-
  Curated as a distinct disease entry rather than as a subtype of Familial Long
  QT Syndrome. Although MONDO places Andersen-Tawil syndrome under familial
  long QT syndrome (via the historical LQT7 designation), ATS is a multisystem
  disorder whose skeletal-muscle and developmental manifestations are not
  captured by an LQTS subtype row, and whose electrocardiographic signature
  (prolonged QU with prominent U waves and frequent resting ectopy, often with
  a normal QTc) differs from classical LQTS. Bidirectional ventricular
  tachycardia makes catecholaminergic polymorphic ventricular tachycardia
  (RYR2 CPVT) the key clinical differential; the distinguishing features are
  frequent ectopy at rest in ATS versus exercise-emergent arrhythmia in CPVT,
  plus the ATS dysmorphism and periodic paralysis.
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0008222
      label: Andersen-Tawil syndrome
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0008222 is the primary disease term for this entry, cross-referenced
      to OMIM:170390 and Orphanet:37553 with KCNJ2 as the asserted causal gene.
references:
- reference: PMID:20301441
  title: "Andersen-Tawil Syndrome."
  tags:
  - GeneReviews
inheritance:
- name: Autosomal Dominant
  description: >-
    ATS is inherited in an autosomal dominant manner with variable expressivity
    and incomplete penetrance. Up to half of affected individuals carry a de
    novo pathogenic variant, so a negative family history does not exclude the
    diagnosis. Expressivity is strikingly variable even within a single family,
    and not all affected individuals manifest the complete triad.
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ATS is inherited in an autosomal dominant manner. At least 50% of individuals diagnosed with ATS have an affected parent. Up to 50% of affected individuals have ATS as the result of a de novo pathogenic variant."
    explanation: GeneReviews states the autosomal dominant inheritance pattern and the high de novo rate.
  - reference: PMID:24827800
    reference_title: "Electrocardiogram in Andersen-Tawil syndrome. New electrocardiographic criteria for diagnosis of type-1 Andersen-Tawil syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Andersen - Tawil syndrome (ATS) is an autosomal - dominant or sporadic disorder characterized by ventricular arrhythmias, periodic paralysis, and distinctive facial and skeletal dysmorphism."
    explanation: Independent review confirms autosomal dominant or sporadic inheritance alongside the defining triad.
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Each child of an individual with ATS has a 50% chance of inheriting the disorder."
    explanation: GeneReviews gives the per-child transmission risk used in genetic counseling of an affected parent.
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Prenatal diagnosis for pregnancies at increased risk is possible if the KCNJ2 pathogenic variant has been identified in an affected family member."
    explanation: >-
      GeneReviews states that prenatal diagnosis is available once the familial
      KCNJ2 variant is known, which is the reproductive-options half of the
      counseling discussion.
prevalence:
- population: Worldwide
  measure_type: POINT_PREVALENCE
  prevalence_class: ULTRA_RARE
  notes: >-
    ATS is consistently described as a very rare orphan channelopathy. Deep
    research summaries commonly quote an order-of-magnitude estimate near 1 per
    1,000,000, but no abstract-level source with a citable numeric interval was
    available, so only the qualitative band is asserted here.
  evidence:
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Andersen-Tawil syndrome (ATS) is a very rare orphan genetic multisystem channelopathy without structural heart disease (with rare exceptions)."
    explanation: Review characterizes ATS as a very rare orphan disorder, supporting the ULTRA_RARE qualitative band.
genetic:
- name: KCNJ2
  notes: >-
    KCNJ2 encodes the alpha subunit of the strong inward-rectifier potassium
    channel Kir2.1, which assembles as a homotetramer. Pathogenic variants are
    predominantly heterozygous missense changes distributed across the channel,
    with in-frame deletions also reported. Loss of function arises through
    impaired plasma-membrane trafficking, reduced conductance or altered
    gating, and weakened coupling to phosphatidylinositol 4,5-bisphosphate
    (PIP2). Because mutant and wild-type subunits coassemble into the same
    tetramer, many variants exert a dominant-negative effect that suppresses
    current well below the 50% expected from simple haploinsufficiency.
    KCNJ2 variants account for roughly 50-60% of clinically diagnosed ATS
    (ATS type 1).
  gene_term:
    preferred_term: KCNJ2
    term:
      id: hgnc:6263
      label: KCNJ2
  relationship_type: CAUSATIVE
  evidence:
  - reference: PMID:11371347
    reference_title: "Mutations in Kir2.1 cause the developmental and episodic electrical phenotypes of Andersen's syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A missense mutation in KCNJ2 (encoding D71V) was identified in the linked family. Eight additional mutations were identified in unrelated patients."
    explanation: The original linkage and mutation-identification study establishing KCNJ2 as the ATS gene.
  - reference: PMID:24827800
    reference_title: "Electrocardiogram in Andersen-Tawil syndrome. New electrocardiographic criteria for diagnosis of type-1 Andersen-Tawil syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "KCNJ2 mutations are detectable in up to 60 % of patients with ATS."
    explanation: Quantifies the diagnostic yield of KCNJ2 testing in clinically diagnosed ATS.
  - reference: PMID:17395133
    reference_title: "Management and treatment of Andersen-Tawil syndrome (ATS)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mechanisms of disruption of channel function include abnormal trafficking and assembly of second messengers such as phosphatidylinositol 4,5-bisphosphate, abnormal gating of the channel, and incorrect folding of the Kir2.1 protein."
    explanation: Enumerates the molecular routes by which KCNJ2 variants produce Kir2.1 loss of function.
  case_fractions:
  - population: Clinically diagnosed ATS
    case_fraction_low: 50.0
    case_fraction_high: 60.0
    notes: KCNJ2 (ATS type 1) accounts for approximately 50-60% of clinically diagnosed ATS.
    evidence:
    - reference: PMID:32947483
      reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "ATS type 1 is inherited in an autosomal dominant fashion and is caused by mutations in the KCNJ2 gene, which encodes the α subunit of the K+ channel protein Kir2.1 (in ≈ 50-60% of cases)."
      explanation: Gives the share of ATS cases explained by KCNJ2.
- name: KCNJ5
  notes: >-
    A minority of ATS has been attributed to variants in KCNJ5, which encodes
    Kir3.4 (GIRK4), the G-protein-gated inwardly rectifying potassium channel
    carrying the acetylcholine-activated potassium current. This assignment is
    reported in review literature but rests on far fewer families than the
    KCNJ2 evidence and should be treated as a less well established locus.
  gene_term:
    preferred_term: KCNJ5
    term:
      id: hgnc:6266
      label: KCNJ5
  relationship_type: CAUSATIVE
  evidence:
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "ATS type 2 is in turn linked to a rare mutation in the KCNJ5-GIRK4 gene that encodes the G protein-sensitive-activated inwardly rectifying K+ channel Kir3.4 (15%), which carries the acetylcholine-induced potassium current."
    explanation: >-
      Review attributes a minority of ATS to KCNJ5. Marked PARTIAL because this
      assignment is not consistently replicated; other reviews describe
      KCNJ2-negative ATS as genetically unresolved rather than KCNJ5-related.
- name: Genetically unsolved ATS
  notes: >-
    A substantial fraction of clinically diagnosed ATS has no identified
    pathogenic variant. Historically labelled ATS type 2, this is a clinical
    residue category rather than a defined locus: affected individuals are
    clinically indistinguishable from ATS type 1.
  relationship_type: UNKNOWN
  evidence:
  - reference: PMID:24383070
    reference_title: "Andersen-Tawil syndrome: clinical and molecular aspects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In ATS type 2 (ATS2), which does not differ from ATS1 in its clinical symptoms, the genetic defect is unknown."
    explanation: Establishes that ATS2 is a genetically unresolved residue category, clinically identical to ATS1.
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "About 30% of cases are de novo/sporadic, suggesting that additional as-yet unidentified genes also cause the disorder."
    explanation: Supports the existence of additional, currently unidentified ATS loci.
mechanistic_hypotheses:
- hypothesis_group_id: single_channel_three_tissue_divergence
  hypothesis_label: Single-Channel Three-Tissue Divergence Model
  status: CANONICAL
  description: >-
    One Kir2.1 loss-of-function lesion produces three clinically unrelated
    manifestations because the same channel serves three distinct roles in
    three tissues: terminal repolarization and resting potential in
    cardiomyocytes and Purkinje fibers (yielding ventricular ectopy and
    bidirectional ventricular tachycardia); resting potential and excitability
    in skeletal myofibers (yielding potassium-sensitive periodic paralysis);
    and bioelectric patterning of the anterior ectoderm during neurulation
    (yielding craniofacial and skeletal dysmorphism). The cardiac and
    skeletal-muscle arms are excitability phenomena; the developmental arm is
    a non-excitable, voltage-mediated morphogenetic phenomenon.
  evidence:
  - reference: PMID:11371347
    reference_title: "Mutations in Kir2.1 cause the developmental and episodic electrical phenotypes of Andersen's syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These findings suggest that Kir2.1 plays an important role in developmental signaling in addition to its previously recognized function in controlling cell excitability in skeletal muscle and heart."
    explanation: >-
      The founding paper explicitly frames the divergence: one channel with an
      excitability role in heart and skeletal muscle plus a separate
      developmental-signalling role.
  - reference: PMID:24383070
    reference_title: "Andersen-Tawil syndrome: clinical and molecular aspects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The loss-of-function mutations in KCNJ2 in ATS1 affect the excitability of both skeletal and cardiac muscle, which underlies the cardiac arrhythmias and periodic paralysis associated with ATS. Thus far, the molecular mechanism of the dysmorphic features is only poorly understood."
    explanation: >-
      Confirms the two excitability arms and flags the developmental arm as the
      least understood branch of the divergence.
discussions:
- discussion_id: gap_ats_developmental_mechanism_in_human
  prompt: >-
    Is the craniofacial and skeletal dysmorphism of Andersen-Tawil syndrome
    caused by loss of Kir2.1-dependent bioelectric patterning of the anterior
    ectoderm during human neurulation, as demonstrated in Xenopus, and does the
    same voltage-mediated mechanism operate in human cranial neural crest and
    placode lineages?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Disrupted Bioelectric Craniofacial Patterning
  rationale: >-
    The bioelectric mechanism for ATS dysmorphism is established in Xenopus
    laevis by misexpression of human ATS-associated KCNJ2 variants, optogenetic
    voltage manipulation, and rescue with unrelated ion translocators. No
    equivalent human tissue experiment exists, and human review literature
    continues to describe the dysmorphism mechanism as poorly understood. The
    mismatch matters because the frog work predicts a narrow, early neurula
    critical window and therefore a specific (and otherwise implausible)
    therapeutic opportunity for ion-flux-modifying drugs, a prediction that
    cannot be acted on without human-relevant confirmation.
  proposed_experiments:
  - experiment_id: exp_ats_human_ncc_voltage_patterning
    name: Voltage and patterning-gene readout in human ATS cranial neural crest
    description: >-
      Measure resting membrane potential regionalization and craniofacial
      patterning gene expression in human iPSC-derived cranial neural crest
      and placodal ectoderm carrying ATS KCNJ2 variants versus isogenic
      corrected controls.
  - experiment_id: exp_ats_human_kcnj2_ectoderm_expression
    name: Human anterior-ectoderm KCNJ2 expression atlas query
    description: >-
      Determine whether human KCNJ2 is expressed in the anterior ectoderm at
      the human developmental stage corresponding to the Xenopus neurula
      critical window, using human embryonic single-cell atlases.
  - experiment_id: exp_ats_voltage_rescue_organoid
    name: Pharmacological voltage-normalization rescue in mutant human neural crest organoids
    description: >-
      Test whether pharmacological normalization of membrane voltage in
      KCNJ2-mutant human neural crest organoids restores the disrupted
      craniofacial patterning gene expression domains.
- discussion_id: gap_ats_flecainide_variant_specific_safety
  prompt: >-
    Is flecainide safe and effective across Andersen-Tawil syndrome type 1, or
    is its effect variant-specific, with some Kir2.1 variants converting a
    class-Ic antiarrhythmic into a proarrhythmic agent?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Delayed Terminal Repolarization and Triggered Activity
  rationale: >-
    Flecainide is widely used in ATS1 and is endorsed empirically by
    GeneReviews, yet a 2024 preprint reported that only 23% of reviewed
    patients had a genuine arrhythmia reduction, 13.5% suffered non-fatal
    cardiac arrest, and mouse and patient-derived iPSC models showed
    variant-dependent proarrhythmia. If confirmed, therapy selection in ATS
    would need to be genotype-stratified rather than uniform. The evidence is
    currently preprint-level and requires peer-reviewed replication.
  proposed_experiments:
  - experiment_id: exp_ats_genotype_stratified_aad_registry
    name: Prospective genotype-stratified antiarrhythmic registry in ATS1
    description: >-
      Conduct a prospective, genotype-stratified registry of antiarrhythmic
      response and adverse events in ATS1, powered to compare
      trafficking-defective versus gating-defective Kir2.1 variants.
  - experiment_id: exp_ats_ipsc_flecainide_panel
    name: Flecainide effect panel across ATS1 patient-derived iPSC cardiomyocyte lines
    description: >-
      Systematically measure the effect of flecainide on IK1 and INa across a
      panel of patient-derived iPSC cardiomyocyte lines representing the
      common ATS1 variant classes.
pathophysiology:
- name: KCNJ2 Loss-of-Function Variant
  description: >-
    A germline, usually heterozygous loss-of-function variant in KCNJ2 alters
    the Kir2.1 strong inward-rectifier potassium channel. Reported mechanisms
    include defective trafficking of the channel to the surface membrane,
    altered gating, misfolding, and weakened coupling to PIP2. This is the
    upstream trigger of the entire ATS phenotype, and it is the ATS-specific
    substitution into the generic channelopathy module trigger node.
  role: trigger
  conforms_to: "cardiac_ion_channel_repolarization#Cardiac Ion-Channel or Calcium-Handling Variant"
  genes:
  - preferred_term: KCNJ2
    term:
      id: hgnc:6263
      label: KCNJ2
  molecular_functions:
  - preferred_term: inward rectifier potassium channel activity
    term:
      id: GO:0005242
      label: inward rectifier potassium channel activity
    modifier: DECREASED
  evidence:
  - reference: PMID:11371347
    reference_title: "Mutations in Kir2.1 cause the developmental and episodic electrical phenotypes of Andersen's syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We have mapped an Andersen's locus to chromosome 17q23 near the inward rectifying potassium channel gene KCNJ2."
    explanation: Establishes KCNJ2 as the mapped ATS locus, the upstream trigger of the mechanism chain.
  - reference: PMID:21148745
    reference_title: "Biophysical and molecular characterization of a novel de novo KCNJ2 mutation associated with Andersen-Tawil syndrome and catecholaminergic polymorphic ventricular tachycardia mimicry."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Immunocytochemical analysis indicates that impaired trafficking of R260P-KCNJ2 channels."
    explanation: Demonstrates defective surface trafficking as one route to Kir2.1 loss of function.
  downstream:
  - target: Dominant-Negative Kir2.1 Tetramer Dysfunction
    description: >-
      Mutant subunits are transcribed and translated and coassemble with
      wild-type subunits into the obligate Kir2.1 tetramer.
    causal_link_type: DIRECT
- name: Dominant-Negative Kir2.1 Tetramer Dysfunction
  description: >-
    Kir2.1 functions as a homotetramer, so mutant and wild-type subunits
    coassemble into mixed channels. A single mutant subunit can poison the
    tetramer, so current falls far below the 50% predicted by
    haploinsufficiency. This dominant-negative amplification explains both the
    autosomal dominant inheritance and the severity of the current deficit, and
    it is the single molecular lesion from which the three tissue-specific arms
    of the disease diverge.
  role: central_effector
  molecular_functions:
  - preferred_term: inward rectifier potassium channel activity
    term:
      id: GO:0005242
      label: inward rectifier potassium channel activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: potassium ion transmembrane transport
    term:
      id: GO:0071805
      label: potassium ion transmembrane transport
    modifier: DECREASED
  evidence:
  - reference: PMID:11371347
    reference_title: "Mutations in Kir2.1 cause the developmental and episodic electrical phenotypes of Andersen's syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Expression of two of these mutations in Xenopus oocytes revealed loss of function and a dominant negative effect in Kir2.1 current as assayed by voltage-clamp."
    explanation: Direct voltage-clamp demonstration of the dominant-negative effect on Kir2.1 current.
  - reference: PMID:21148745
    reference_title: "Biophysical and molecular characterization of a novel de novo KCNJ2 mutation associated with Andersen-Tawil syndrome and catecholaminergic polymorphic ventricular tachycardia mimicry."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The R260P mutation produces a strong dominant negative effect leading to marked suppression of IK1 secondary to a trafficking defect."
    explanation: Quantified dominant-negative suppression of IK1 by a heterozygously expressed ATS variant.
  - reference: PMID:29018970
    reference_title: "Andersen's syndrome mutants produce a knockdown of inwardly rectifying K(+) channel in mouse skeletal muscle in vivo."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "AS has been directly linked to over 40 different autosomal dominant negative loss-of-function mutations in the KCNJ2 gene, encoding for the tetrameric strong inward rectifying K+ channel KIR2.1."
    explanation: Confirms the tetrameric architecture that makes dominant-negative suppression possible.
  downstream:
  - target: Reduced Cardiac Inward Rectifier Current
    description: >-
      Kir2.1 is the principal carrier of cardiac IK1 in working ventricular
      myocardium and Purkinje fibres, so tetramer dysfunction lowers IK1.
    causal_link_type: DIRECT
  - target: Reduced Skeletal Muscle Inward Rectifier Current
    description: >-
      The same channel sets resting potential in skeletal myofibers, so the
      identical lesion produces a parallel current deficit in muscle.
    causal_link_type: DIRECT
  - target: Disrupted Bioelectric Craniofacial Patterning
    description: >-
      Beyond excitable tissue, Kir2.1-dependent potassium flux patterns resting
      membrane voltage in the anterior ectoderm during early neurulation.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - loss of regionalized resting membrane potential in the anterior ectoderm
    - disrupted expression of craniofacial patterning genes
  - target: Learning Difficulties
    description: >-
      A distinct neurocognitive phenotype accompanies the classic triad. The
      intermediate steps linking Kir2.1 loss to executive-function and
      abstract-reasoning deficits are not established.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- name: Reduced Cardiac Inward Rectifier Current
  description: >-
    Loss of Kir2.1 lowers the cardiac inward-rectifier current IK1. IK1 has two
    jobs in the ventricular myocyte: it clamps the phase-4 resting membrane
    potential near the potassium equilibrium potential, and its strong inward
    rectification means it supplies most of the repolarizing current in the
    terminal (phase 3) portion of the action potential while contributing
    almost nothing during the plateau. Reducing it therefore destabilizes the
    resting potential and prolongs terminal repolarization, which is registered
    on the surface electrocardiogram as a prolonged QU interval with prominent
    U waves rather than as marked QTc prolongation.
  role: central_effector
  conforms_to: "cardiac_ion_channel_repolarization#Altered Action Potential and Calcium Handling"
  cell_types:
  - preferred_term: cardiomyocyte
    term:
      id: CL:0000746
      label: cardiac muscle cell
  - preferred_term: cardiac Purkinje fibre cell
    term:
      id: CL:0002068
      label: Purkinje myocyte
  biological_processes:
  - preferred_term: membrane repolarization during cardiac muscle cell action potential
    term:
      id: GO:0086013
      label: membrane repolarization during cardiac muscle cell action potential
    modifier: DECREASED
  - preferred_term: regulation of membrane potential
    term:
      id: GO:0042391
      label: regulation of membrane potential
    modifier: DYSREGULATED
  evidence:
  - reference: PMID:38528561
    reference_title: "Transcriptome and open chromatin analysis reveals the process of myocardial cell development and key pathogenic target proteins in Long QT syndrome type 7."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The spontaneous pulsation rate of myocardial cells in the mutation group was significantly lower than that in the repair CRISPR group, the action potential duration was prolonged, and the Kir2.1 current of the inward rectifier potassium ion channel was decreased, which is consistent with the clinical symptoms of ATS patients."
    explanation: >-
      Isogenic CRISPR-corrected patient iPSC cardiomyocytes show reduced Kir2.1
      current and prolonged action potential duration, tying the KCNJ2 variant
      causally to the cardiac electrophysiologic defect.
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Prolongation of the QU/QUc intervals and normal or minimally prolonged QT/QTc intervals with a tendency to ventricular arrhythmias are typical repolarization changes."
    explanation: >-
      Establishes that the surface electrocardiographic signature is QU
      prolongation with a normal or near-normal QTc, the reason LQT7 is a
      misleading label for ATS.
  downstream:
  - target: Delayed Terminal Repolarization and Triggered Activity
    description: >-
      Loss of terminal repolarizing current prolongs late phase 3 and leaves
      the myocyte vulnerable to afterdepolarization-driven triggered beats.
    causal_link_type: DIRECT
- name: Delayed Terminal Repolarization and Triggered Activity
  description: >-
    With IK1 reduced, the late phase-3 repolarizing brake is weakened and the
    resting potential is less firmly clamped, so residual depolarizing drive
    (including sodium-calcium exchanger current responding to cytosolic
    calcium) more readily reaches threshold. The result is delayed
    afterdepolarizations and triggered beats arising at rest, which is why ATS
    produces heavy resting ventricular ectopy rather than the
    exercise-restricted arrhythmia of catecholaminergic polymorphic
    ventricular tachycardia. This is the ATS-specific instance of the
    arrhythmogenic substrate node of the cardiac channelopathy module, and it
    is the pharmacological target of the variant-specific flecainide debate.
  role: amplifier
  conforms_to: "cardiac_ion_channel_repolarization#Arrhythmogenic Substrate and Triggered Activity"
  cell_types:
  - preferred_term: cardiomyocyte
    term:
      id: CL:0000746
      label: cardiac muscle cell
  biological_processes:
  - preferred_term: cardiac muscle cell action potential
    term:
      id: GO:0086001
      label: cardiac muscle cell action potential
    modifier: ABNORMAL
  evidence:
  - reference: PMID:24827800
    reference_title: "Electrocardiogram in Andersen-Tawil syndrome. New electrocardiographic criteria for diagnosis of type-1 Andersen-Tawil syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presence of frequent PVCs at rest are helpful in distinguishing ATS from typical catecholaminergic polymorphic ventricular tachycardia (CPVT). In typical CPVT, rapid PMVT and BiVT usually manifest during or after exercising."
    explanation: >-
      Supports triggered ectopy arising at rest as the ATS-specific character of
      the arrhythmogenic substrate, distinguishing it from CPVT.
  - reference: PMID:39711719
    reference_title: "Kir2.1 mutations differentially increase the risk of flecainide proarrhythmia in Andersen Tawil Syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Kir2.1 mutations impacting the resting membrane potential and cellular excitability create a substrate for life-threatening arrhythmias, raising significant concern about using these drugs in some ATS1 patients."
    explanation: >-
      Links the resting-potential/excitability defect explicitly to formation of
      an arrhythmogenic substrate in cardiac-specific ATS1 mouse models.
  downstream:
  - target: Bidirectional and Polymorphic Ventricular Tachycardia
    description: >-
      Triggered beats arising on this substrate organize into bidirectional and
      polymorphic ventricular tachycardia.
    causal_link_type: DIRECT
- name: Bidirectional and Polymorphic Ventricular Tachycardia
  description: >-
    The characteristic sustained rhythm of ATS is bidirectional ventricular
    tachycardia, a form of polymorphic ventricular tachycardia in which the QRS
    axis alternates beat to beat. Frequent premature ventricular contractions,
    couplets, and bigeminy are the far more common everyday manifestation.
    Torsade de pointes is comparatively rare in ATS despite the LQT7 label.
  role: effector
  conforms_to: "cardiac_ion_channel_repolarization#Ventricular Tachyarrhythmia"
  cell_types:
  - preferred_term: cardiomyocyte
    term:
      id: CL:0000746
      label: cardiac muscle cell
  evidence:
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bidirectional ventricular tachycardia is the hallmark ventricular arrhythmia, but also premature ventricular contractions, and rarely, polymorphic ventricular tachycardia of torsade de pointes type may be present."
    explanation: Identifies bidirectional ventricular tachycardia as the hallmark ATS rhythm.
  - reference: PMID:21148745
    reference_title: "Biophysical and molecular characterization of a novel de novo KCNJ2 mutation associated with Andersen-Tawil syndrome and catecholaminergic polymorphic ventricular tachycardia mimicry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our proband displayed dysmorphic features including micrognathia, clinodactyly, and syndactyly and exhibited multiform extrasystoles and bidirectional ventricular tachycardia both at rest and during exercise testing."
    explanation: >-
      Case-level demonstration of bidirectional ventricular tachycardia present
      at rest as well as with exercise in a molecularly confirmed ATS patient.
  downstream:
  - target: Ventricular Arrhythmia
    description: >-
      Ventricular electrical instability is the cardinal cardiac manifestation
      of the disease, spanning isolated ectopy through sustained tachyarrhythmia.
    causal_link_type: DIRECT
  - target: Bidirectional Ventricular Tachycardia
    description: The rhythm itself is the observed clinical phenotype.
    causal_link_type: DIRECT
  - target: Premature Ventricular Contractions
    description: Triggered ectopic beats are recorded as frequent premature ventricular contractions.
    causal_link_type: DIRECT
  - target: Prominent U Wave
    description: >-
      Delayed terminal repolarization from reduced IK1 is registered on the
      surface electrocardiogram as a prolonged QU interval with a prominent U wave.
    causal_link_type: DIRECT
  - target: Prolonged QT Interval
    description: >-
      QT prolongation is present in a subset and gave rise to the historical
      LQT7 designation, though QTc is often normal or only mildly prolonged.
    causal_link_type: DIRECT
  - target: Palpitations
    description: Frequent ectopy and runs of ventricular tachycardia are perceived as palpitations.
    causal_link_type: DIRECT
  - target: Arrhythmic Loss of Cardiac Output
    description: >-
      Sustained or rapid ventricular tachycardia abolishes effective cardiac
      output.
    causal_link_type: DIRECT
- name: Arrhythmic Loss of Cardiac Output
  description: >-
    When a ventricular tachyarrhythmia is sustained or degenerates, cardiac
    output falls and cerebral perfusion is lost, producing syncope and, if the
    rhythm does not terminate, sudden cardiac death. Life-threatening events
    are far less common in ATS than the ectopic burden would suggest, but they
    do occur and are the reason for rhythm surveillance and, in selected
    patients, defibrillator implantation.
  role: outcome
  conforms_to: "cardiac_ion_channel_repolarization#Syncope and Sudden Cardiac Death"
  evidence:
  - reference: PMID:24861851
    reference_title: "Andersen-Tawil syndrome: report of 3 novel mutations and high risk of symptomatic cardiac involvement."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "KCNJ2 mutations cause a variable phenotype, with dysmorphic features seen in all patients studied, a high penetrance of periodic paralysis in males and ventricular arrhythmia with a risk of sudden cardiac death."
    explanation: Establishes sudden cardiac death as a real risk of the ATS ventricular arrhythmia.
  - reference: PMID:24861851
    reference_title: "Andersen-Tawil syndrome: report of 3 novel mutations and high risk of symptomatic cardiac involvement."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two patients (with T75M and T309I mutations) had aborted sudden cardiac death. An implantable cardioverter-defibrillator was utilized in 40% of cases."
    explanation: Documents aborted sudden cardiac death events and defibrillator use in a molecularly defined ATS cohort.
  downstream:
  - target: Syncope
    description: Transient arrhythmia-induced cerebral hypoperfusion causes syncope.
    causal_link_type: DIRECT
  - target: Sudden Cardiac Death
    description: A ventricular tachyarrhythmia that does not terminate causes sudden cardiac death.
    causal_link_type: DIRECT
- name: Reduced Skeletal Muscle Inward Rectifier Current
  description: >-
    The second arm of the divergence. Kir2.1 is also the dominant
    inward-rectifier channel of the skeletal myofiber sarcolemma and transverse
    tubules, where it holds the resting membrane potential near the potassium
    equilibrium potential. Myotubes cultured from ATS patients lack the
    inwardly rectifying barium-sensitive current entirely, and their resting
    potential shifts in the depolarizing direction. Importantly, ATS myoblasts
    show no morphological, proliferative, or fusion defect, so the muscle
    phenotype is electrical rather than dystrophic.
  role: central_effector
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: regulation of membrane potential
    term:
      id: GO:0042391
      label: regulation of membrane potential
    modifier: DYSREGULATED
  - preferred_term: potassium ion transmembrane transport
    term:
      id: GO:0071805
      label: potassium ion transmembrane transport
    modifier: DECREASED
  evidence:
  - reference: PMID:19570891
    reference_title: "Mechanisms underlying Andersen's syndrome pathology in skeletal muscle are revealed in human myotubes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Current recordings carried out on myotubes revealed the absence of an inwardly rectifying Ba2+-sensitive current in affected patient cells. One consequence of the Ik1 current loss in Andersen's syndrome myotubes is a shift of the resting membrane potential toward depolarizing potentials."
    explanation: >-
      Ex vivo human patient myotubes show loss of the inward rectifier current
      and consequent depolarization of the resting membrane potential.
  - reference: PMID:29018970
    reference_title: "Andersen's syndrome mutants produce a knockdown of inwardly rectifying K(+) channel in mouse skeletal muscle in vivo."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Whole-cell voltage-clamp recordings in individual skeletal muscle fibers confirmed the reduction of inwardly rectifying K+ current (IK1) after transduction with ∆314-315 KIR2.1 as compared to WT channels."
    explanation: In vivo mouse confirmation that an ATS variant reduces skeletal muscle IK1.
  downstream:
  - target: Paradoxical Sarcolemmal Depolarization and Inexcitability
    description: >-
      With the resting potential no longer clamped, potassium shifts drive the
      fiber into sustained depolarization instead of restoring excitability.
    causal_link_type: DIRECT
- name: Paradoxical Sarcolemmal Depolarization and Inexcitability
  description: >-
    Normally, a fall or rise in extracellular potassium is buffered by the
    strong inward rectifier, which holds resting potential near the potassium
    equilibrium potential. With Kir2.1 lost, that buffering fails and the fiber
    depolarizes paradoxically during potassium shifts. Sustained depolarization
    inactivates the voltage-gated sodium channels and the fiber becomes
    electrically inexcitable despite being structurally intact, producing
    flaccid weakness that resolves as the potassium disturbance corrects. This
    is why attacks in ATS may be hypokalaemic, hyperkalaemic, or normokalaemic:
    the defect is the loss of buffering, not a fixed direction of potassium
    sensitivity.
  role: effector
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: skeletal muscle contraction
    term:
      id: GO:0003009
      label: skeletal muscle contraction
    modifier: DECREASED
  evidence:
  - reference: PMID:17395133
    reference_title: "Management and treatment of Andersen-Tawil syndrome (ATS)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The skeletal muscle and cardiac symptoms are accounted for, in most cases, by a dominant negative effect of the mutations on potassium channel current, resulting in prolonged depolarization of the action potential."
    explanation: >-
      States the prolonged-depolarization mechanism shared by the cardiac and
      skeletal-muscle arms of the disease.
  - reference: PMID:29018970
    reference_title: "Andersen's syndrome mutants produce a knockdown of inwardly rectifying K(+) channel in mouse skeletal muscle in vivo."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Analysis of skeletal muscle function revealed reduced force generation during isometric contraction as well as reduced resistance to muscle fatigue in extensor digitorum longus muscles transduced with AS mutant KIR2.1."
    explanation: >-
      Demonstrates that the IK1 deficit translates into a measurable
      contractile-function deficit in intact muscle.
  - reference: PMID:24861851
    reference_title: "Andersen-Tawil syndrome: report of 3 novel mutations and high risk of symptomatic cardiac involvement."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients had dysmorphic features; periodic paralysis affected males more frequently than females (80% vs. 20%), and most attacks were normokalemic."
    explanation: >-
      Supports the observation that ATS attacks are not fixed to one direction
      of potassium disturbance and are frequently normokalaemic.
  downstream:
  - target: Periodic Paralysis
    description: Episodic fiber inexcitability presents clinically as periodic paralysis.
    causal_link_type: DIRECT
  - target: Episodic Flaccid Weakness
    description: >-
      Loss of fiber excitability produces flaccid rather than spastic weakness,
      with preserved muscle structure between attacks.
    causal_link_type: DIRECT
  - target: Muscle Weakness
    description: >-
      Repeated or persistent electrical dysfunction contributes to mild fixed
      interictal weakness in many affected individuals.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- name: Disrupted Bioelectric Craniofacial Patterning
  description: >-
    The third arm of the divergence, and the least understood. Beyond its role
    in excitable tissue, Kir2.1-dependent potassium flux establishes a
    regionalized pattern of resting membrane potential across the anterior
    ectoderm during early neurulation. This voltage pattern acts as a
    morphogenetic instruction: in Xenopus, misexpressing human ATS-associated
    KCNJ2 variants disrupts the voltage map, derails ten craniofacial
    patterning genes including cranial neural crest and placode markers, and
    produces craniofacial anomalies in the same structures affected in humans.
    Critically, the effect is voltage-specific rather than channel-specific:
    unrelated ion translocators that change membrane voltage reproduce the
    anomalies, whereas electroneutral or inactive channels do not. The
    resulting malformations are developmental and fixed, unlike the episodic
    cardiac and muscular manifestations.
  role: effector
  cell_types:
  - preferred_term: migratory cranial neural crest cell
    term:
      id: CL:0000333
      label: migratory neural crest cell
  biological_processes:
  - preferred_term: regulation of membrane potential
    term:
      id: GO:0042391
      label: regulation of membrane potential
    modifier: DYSREGULATED
  - preferred_term: embryonic cranial skeleton morphogenesis
    term:
      id: GO:0048701
      label: embryonic cranial skeleton morphogenesis
    modifier: ABNORMAL
  evidence:
  - reference: PMID:26864374
    reference_title: "Bioelectric signalling via potassium channels: a mechanism for craniofacial dysmorphogenesis in KCNJ2-associated Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Misexpression in Xenopus of KCNJ2 carrying ATS-associated mutations causes CFAs in the same structures affected in humans, changes the normal pattern of membrane voltage potential regionalization in the developing face and disrupts expression of important craniofacial patterning genes, revealing the endogenous control of craniofacial patterning by bioelectric cell states."
    explanation: >-
      Provides the mechanistic model for the developmental arm: human ATS KCNJ2
      variants disrupt the ectodermal voltage map and craniofacial patterning
      gene expression in Xenopus.
  - reference: PMID:26864374
    reference_title: "Bioelectric signalling via potassium channels: a mechanism for craniofacial dysmorphogenesis in KCNJ2-associated Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We predict that the critical time is early during neurulation, and the critical cells are the ectodermal cranial neural crest and placode lineages."
    explanation: Identifies the neurula-stage critical window and the cranial neural crest and placode lineages.
  - reference: PMID:24383070
    reference_title: "Andersen-Tawil syndrome: clinical and molecular aspects."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Thus far, the molecular mechanism of the dysmorphic features is only poorly understood."
    explanation: >-
      Human review literature explicitly flags the developmental arm as
      incompletely understood, which is why the Xenopus evidence is carried with
      an accompanying HUMAN_MODEL_MISMATCH discussion.
  downstream:
  - target: Low-Set Ears
    description: Disrupted arch and placode-derived patterning affects external ear position.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Hypertelorism
    description: Altered midfacial patterning widens interorbital spacing.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Micrognathia
    description: Disrupted mandibular arch patterning produces a small or receding mandible.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Broad Forehead
    description: Altered anterior ectodermal patterning produces a broad forehead.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Clinodactyly of the 5th Finger
    description: >-
      Kir2.1-dependent bioelectric patterning also operates in limb development,
      producing incurving of the fifth digit.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Syndactyly
    description: Digit separation is incomplete, most often affecting the toes.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Short Stature
    description: Skeletal growth is reduced as part of the developmental phenotype.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Scoliosis
    description: Axial skeletal patterning is affected, producing scoliosis.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
phenotypes:
- category: Cardiovascular
  name: Ventricular Arrhythmia
  description: >-
    Ventricular electrical instability is one of the three cardinal
    manifestations of ATS, ranging from asymptomatic ectopy to sustained
    tachyarrhythmia.
  phenotype_term:
    preferred_term: Ventricular arrhythmia
    term:
      id: HP:0004308
      label: Ventricular arrhythmia
  frequency: FREQUENT
  evidence:
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "About 60% of affected individuals have all features of the major triad."
    explanation: >-
      Supports FREQUENT (30-79%) for the triad components: about 60% of affected
      individuals manifest all three, so each component is at least that common.
- category: Cardiovascular
  name: Bidirectional Ventricular Tachycardia
  description: >-
    Polymorphic ventricular tachycardia in which the QRS axis alternates from
    beat to beat. This is the hallmark ATS rhythm and the feature that most
    closely mimics catecholaminergic polymorphic ventricular tachycardia.
  phenotype_term:
    preferred_term: Bidirectional ventricular tachycardia
    term:
      id: HP:0034040
      label: Bidirectional ventricular tachycardia
  evidence:
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bidirectional ventricular tachycardia is the hallmark ventricular arrhythmia, but also premature ventricular contractions, and rarely, polymorphic ventricular tachycardia of torsade de pointes type may be present."
    explanation: Identifies bidirectional ventricular tachycardia as the hallmark ATS arrhythmia.
  - reference: PMID:24827800
    reference_title: "Electrocardiogram in Andersen-Tawil syndrome. New electrocardiographic criteria for diagnosis of type-1 Andersen-Tawil syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac manifestations of ATS include frequent premature ventricular contractions (PVC), Q-U interval prolongation, prominent U-waves, and a special type of polymorphic ventricular tachycardia (PMVT) called bidirectional ventricular tachycardia (BiVT)."
    explanation: Independent confirmation of bidirectional ventricular tachycardia as a core cardiac manifestation.
- category: Cardiovascular
  name: Premature Ventricular Contractions
  description: >-
    Frequent ventricular ectopic beats, characteristically present at rest,
    often in couplets or bigeminy. Resting ectopic burden is one of the most
    useful discriminators from catecholaminergic polymorphic ventricular
    tachycardia, in which ectopy is exercise-emergent.
  phenotype_term:
    preferred_term: Premature ventricular contraction
    term:
      id: HP:0006682
      label: Premature ventricular contraction
  evidence:
  - reference: PMID:24827800
    reference_title: "Electrocardiogram in Andersen-Tawil syndrome. New electrocardiographic criteria for diagnosis of type-1 Andersen-Tawil syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PVCs at rest are quite frequent in ATS1 patients, however, in LQTS patients, PVCs and asymptomatic VT are uncommon which also contributes to differentiating them."
    explanation: >-
      Documents frequent resting premature ventricular contractions as a
      characteristic and discriminating ATS finding.
- category: Cardiovascular
  name: Prominent U Wave
  description: >-
    A prominent U wave with a prolonged QU/QUc interval is the characteristic
    electrocardiographic signature of ATS and reflects delayed terminal
    repolarization from reduced IK1. It is a more sensitive marker than QTc,
    which is frequently normal.
  phenotype_term:
    preferred_term: Prominent U wave
    term:
      id: HP:0025072
      label: Prominent U wave
  evidence:
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Prolongation of the QU/QUc intervals and normal or minimally prolonged QT/QTc intervals with a tendency to ventricular arrhythmias are typical repolarization changes."
    explanation: Establishes prolonged QU with a normal or minimally prolonged QT as the typical ATS repolarization signature.
- category: Cardiovascular
  name: Prolonged QT Interval
  description: >-
    QT prolongation occurs in a subset of affected individuals and is the basis
    of the historical LQT7 designation. In practice QTc is often normal or only
    minimally prolonged, so a normal QTc does not exclude ATS and the QU
    interval is the more informative measurement.
  phenotype_term:
    preferred_term: Prolonged QT interval
    term:
      id: HP:0001657
      label: Prolonged QT interval
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ventricular arrhythmias and prolonged QT interval"
    explanation: GeneReviews lists prolonged QT interval as part of the defining ATS triad.
  - reference: PMID:24383070
    reference_title: "Andersen-Tawil syndrome: clinical and molecular aspects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ATS patients may show a prolongation of the QT interval,which explains the classification as long QT syndrome type 7 (LQT7), and specific neurological or neurocognitive defects."
    explanation: Explains the origin of the LQT7 classification while noting QT prolongation is only sometimes present.
- category: Cardiovascular
  name: Palpitations
  description: Perceived awareness of ectopic beats or runs of ventricular tachycardia, often a presenting symptom.
  phenotype_term:
    preferred_term: Palpitations
    term:
      id: HP:0001962
      label: Palpitations
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals present in the first or second decade with either cardiac symptoms (palpitations and/or syncope) or weakness that occurs spontaneously following prolonged rest or following rest after exertion."
    explanation: GeneReviews names palpitations as a common presenting cardiac symptom.
- category: Cardiovascular
  name: Syncope
  description: Transient loss of consciousness from arrhythmia-induced cerebral hypoperfusion; often the sentinel cardiac event.
  phenotype_term:
    preferred_term: Syncope
    term:
      id: HP:0001279
      label: Syncope
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals present in the first or second decade with either cardiac symptoms (palpitations and/or syncope) or weakness that occurs spontaneously following prolonged rest or following rest after exertion."
    explanation: GeneReviews names syncope as a presenting cardiac symptom of ATS.
- category: Cardiovascular
  name: Sudden Cardiac Death
  description: >-
    Unexpected death from a ventricular tachyarrhythmia that does not
    terminate. Life-threatening events are uncommon relative to the ectopic
    burden but are documented and drive risk stratification and defibrillator
    decisions.
  phenotype_term:
    preferred_term: Sudden cardiac death
    term:
      id: HP:0001645
      label: Sudden cardiac death
  evidence:
  - reference: PMID:24861851
    reference_title: "Andersen-Tawil syndrome: report of 3 novel mutations and high risk of symptomatic cardiac involvement."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two patients (with T75M and T309I mutations) had aborted sudden cardiac death. An implantable cardioverter-defibrillator was utilized in 40% of cases."
    explanation: Documents aborted sudden cardiac death in a molecularly confirmed ATS cohort.
- category: Neuromuscular
  name: Periodic Paralysis
  description: >-
    Recurrent episodes of flaccid muscle weakness. Attacks may occur with low,
    normal, or high serum potassium, and are commonly precipitated by prolonged
    rest, rest after exertion, fasting, carbohydrate-rich meals, or cold.
  phenotype_term:
    preferred_term: Periodic paralysis
    term:
      id: HP:0003768
      label: Periodic paralysis
  frequency: FREQUENT
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals present in the first or second decade with either cardiac symptoms (palpitations and/or syncope) or weakness that occurs spontaneously following prolonged rest or following rest after exertion."
    explanation: GeneReviews describes the characteristic triggers of the weakness attacks.
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "About 60% of affected individuals have all features of the major triad."
    explanation: >-
      Supports FREQUENT (30-79%) for the triad components: about 60% of affected
      individuals manifest all three.
- category: Neuromuscular
  name: Episodic Flaccid Weakness
  description: >-
    The specific character of the ATS paralytic attack: flaccid rather than
    spastic weakness, with structurally normal muscle, reflecting electrical
    inexcitability of the sarcolemma rather than muscle destruction.
  phenotype_term:
    preferred_term: Episodic flaccid weakness
    term:
      id: HP:0003752
      label: Episodic flaccid weakness
  evidence:
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The typical muscular change is episodic flaccid muscle weakness."
    explanation: Directly states the flaccid, episodic character of the weakness.
- category: Neuromuscular
  name: Muscle Weakness
  description: >-
    Mild fixed interictal weakness is common, distinguishing ATS from purely
    episodic periodic paralyses in which strength between attacks is normal.
  phenotype_term:
    preferred_term: Muscle weakness
    term:
      id: HP:0001324
      label: Muscle weakness
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mild permanent weakness is common."
    explanation: GeneReviews documents mild fixed interictal weakness as a common feature.
  - reference: PMID:19570891
    reference_title: "Mechanisms underlying Andersen's syndrome pathology in skeletal muscle are revealed in human myotubes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Muscle weakness has been reported in two-thirds of the patients."
    explanation: Quantifies the frequency of muscle weakness in reported ATS patients.
- category: Metabolic
  name: Hypokalemia
  description: >-
    Some ATS paralytic attacks occur with low serum potassium. Potassium
    sensitivity is variable rather than fixed, and a normal interictal potassium
    does not exclude the diagnosis.
  phenotype_term:
    preferred_term: Hypokalemia
    term:
      id: HP:0002900
      label: Hypokalemia
  context: >-
    Recorded as the biochemical setting of a paralytic attack rather than as a
    downstream consequence of the Kir2.1 lesion. The primary defect is loss of
    potassium buffering, so the ictal potassium level defines the attack
    subtype and is deliberately not wired as a downstream edge.
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "For episodic weakness: if serum potassium concentration is low (<3.0 mmol/L), administration of oral potassium"
    explanation: GeneReviews management guidance presupposes hypokalaemic attacks in ATS.
- category: Metabolic
  name: Hyperkalemia
  description: >-
    ATS attacks may also occur with high serum potassium, which is why blanket
    potassium supplementation is unsafe and attacks must be characterized
    biochemically before treatment.
  phenotype_term:
    preferred_term: Hyperkalemia
    term:
      id: HP:0002153
      label: Hyperkalemia
  context: >-
    Recorded as the biochemical setting of a paralytic attack rather than as a
    downstream consequence of the Kir2.1 lesion. Attacks may be hypokalaemic,
    normokalaemic, or hyperkalaemic, which is why potassium must be measured
    before treating an attack.
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "if serum potassium concentration is high, ingesting carbohydrates may lower serum potassium levels"
    explanation: >-
      GeneReviews gives specific management for the hyperkalaemic attack,
      establishing that ATS attacks occur with high potassium as well as low.
- category: Craniofacial
  name: Low-Set Ears
  description: Low-set ears are one of the recognized ATS dysmorphic features.
  phenotype_term:
    preferred_term: Low-set ears
    term:
      id: HP:0000369
      label: Low-set ears
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"
    explanation: GeneReviews lists low-set ears among the defining ATS anomalies.
- category: Craniofacial
  name: Hypertelorism
  description: Widely spaced eyes, a consistent element of the ATS facial gestalt.
  phenotype_term:
    preferred_term: Hypertelorism
    term:
      id: HP:0000316
      label: Hypertelorism
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"
    explanation: GeneReviews lists widely spaced eyes (hypertelorism) among the defining ATS anomalies.
- category: Craniofacial
  name: Micrognathia
  description: >-
    A small or receding mandible ("small mandible" in the GeneReviews anomaly
    list), one of the defining dysmorphic features of the ATS triad.
  notes: >-
    An earlier draft of this entry additionally asserted that micrognathia is a
    risk marker for life-threatening arrhythmic events in ATS. That claim was
    removed because no cited source supports it: the largest ATS1 outcome
    cohort (PMID:32299589, 118 patients from 57 families) identifies a history
    of syncope, documented sustained ventricular tachycardia, and amiodarone
    administration as the predictors of life-threatening arrhythmic events, and
    does not report any dysmorphic feature among them. Those evidenced
    predictors are recorded in the progression section instead.
  phenotype_term:
    preferred_term: Micrognathia
    term:
      id: HP:0000347
      label: Micrognathia
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"
    explanation: GeneReviews lists a small mandible among the defining ATS anomalies.
  - reference: PMID:21148745
    reference_title: "Biophysical and molecular characterization of a novel de novo KCNJ2 mutation associated with Andersen-Tawil syndrome and catecholaminergic polymorphic ventricular tachycardia mimicry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our proband displayed dysmorphic features including micrognathia, clinodactyly, and syndactyly"
    explanation: Case-level documentation of micrognathia in a molecularly confirmed ATS patient.
- category: Craniofacial
  name: Broad Forehead
  description: A broad forehead is part of the characteristic ATS craniofacial gestalt.
  phenotype_term:
    preferred_term: Broad forehead
    term:
      id: HP:0000337
      label: Broad forehead
  evidence:
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with ATS have characteristic physical developmental dysmorphisms that affect the face, skull, limbs, thorax, and stature."
    explanation: >-
      Supports the presence of characteristic facial and skull dysmorphism.
      Marked PARTIAL because the abstract does not enumerate broad forehead
      specifically; the specific feature is drawn from the wider ATS literature.
- category: Skeletal
  name: Clinodactyly of the 5th Finger
  description: Incurving of the fifth finger, one of the most consistently reported ATS limb anomalies.
  phenotype_term:
    preferred_term: Clinodactyly of the 5th finger
    term:
      id: HP:0004209
      label: Clinodactyly of the 5th finger
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"
    explanation: GeneReviews lists fifth-digit clinodactyly among the defining ATS anomalies.
- category: Skeletal
  name: Syndactyly
  description: Incomplete separation of digits, most often of the toes.
  phenotype_term:
    preferred_term: Syndactyly
    term:
      id: HP:0001159
      label: Syndactyly
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"
    explanation: GeneReviews lists syndactyly among the defining ATS anomalies.
- category: Skeletal
  name: Short Stature
  description: Reduced adult height as part of the ATS developmental phenotype.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"
    explanation: GeneReviews lists short stature among the defining ATS anomalies.
- category: Skeletal
  name: Scoliosis
  description: Lateral curvature of the spine, part of the ATS axial skeletal phenotype.
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis"
    explanation: GeneReviews lists scoliosis among the defining ATS anomalies.
- category: Neurocognitive
  name: Learning Difficulties
  description: >-
    Mild learning difficulties with a distinct neurocognitive profile,
    particularly deficits in executive function and abstract reasoning, are
    described in ATS and are frequently overlooked in a disorder framed around
    its triad.
  phenotype_term:
    preferred_term: Specific learning disability
    term:
      id: HP:0001328
      label: Specific learning disability
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mild learning difficulties and a distinct neurocognitive phenotype (i.e., deficits in executive function and abstract reasoning) have been described."
    explanation: GeneReviews documents the neurocognitive phenotype of ATS.
treatments:
- name: Oral Potassium Repletion for Hypokalaemic Attacks
  description: >-
    For a paralytic attack occurring with documented hypokalaemia, oral
    potassium is given until the serum concentration normalizes. Potassium must
    be measured before repletion and cardiac monitoring obtained where
    possible, because ATS attacks may also be normokalaemic or hyperkalaemic
    and blanket supplementation would then be unsafe. If serum potassium is
    high, ingesting carbohydrates instead lowers it.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: oral potassium repletion
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: potassium chloride
      term:
        id: CHEBI:32588
        label: potassium chloride
  target_mechanisms:
  - target: Paradoxical Sarcolemmal Depolarization and Inexcitability
    treatment_effect: INHIBITS
    description: >-
      Correcting the potassium disturbance restores the driving force that the
      unbuffered sarcolemma can no longer maintain, allowing the fiber to
      repolarize and regain excitability.
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "For episodic weakness: if serum potassium concentration is low (<3.0 mmol/L), administration of oral potassium (20-30 mEq/L) every 15-30 minutes (not to exceed 200 mEq in a 12-hour period) until the serum concentration normalizes"
    explanation: GeneReviews gives the specific potassium repletion protocol for hypokalaemic ATS attacks.
- name: Carbonic Anhydrase Inhibitor Prophylaxis
  description: >-
    Carbonic anhydrase inhibitors such as acetazolamide, together with daily
    slow-release potassium supplementation and trigger avoidance, are used to
    reduce the frequency and severity of paralytic attacks. The evidence in ATS
    specifically is limited and largely extrapolated from the other periodic
    paralyses, and electrolyte and renal effects require monitoring.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: carbonic anhydrase inhibitor prophylaxis
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: acetazolamide
      term:
        id: CHEBI:27690
        label: acetazolamide
  target_mechanisms:
  - target: Paradoxical Sarcolemmal Depolarization and Inexcitability
    treatment_effect: INHIBITS
    description: >-
      Prophylaxis is directed at reducing the frequency with which potassium
      shifts drive the unbuffered sarcolemma into inexcitability.
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Reduction in frequency and severity of episodic attacks of weakness with lifestyle/dietary modification to avoid known triggers; use of carbonic anhydrase inhibitors; daily use of slow-release potassium supplements"
    explanation: GeneReviews recommends carbonic anhydrase inhibitors and slow-release potassium for attack prophylaxis.
- name: Flecainide
  description: >-
    Flecainide is used empirically for significant, frequent ventricular
    arrhythmia in ATS and has suppressed bidirectional ventricular tachycardia
    where beta-blockade failed. Its safety is now under active reassessment:
    a 2024 preprint reviewing 53 ATS1 patients found genuine arrhythmia
    reduction in only 23%, non-fatal cardiac arrest in 13.5%, and
    variant-dependent proarrhythmia in mouse and patient-derived iPSC models,
    concluding that class-Ic drugs may be proarrhythmic in some ATS1 patients.
    Separately, GeneReviews cautions that class I antiarrhythmics may
    paradoxically worsen the neuromuscular symptoms, so flecainide is a drug
    whose benefit must be weighed against two distinct hazards.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: flecainide therapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: flecainide
      term:
        id: CHEBI:75984
        label: flecainide
  target_mechanisms:
  - target: Delayed Terminal Repolarization and Triggered Activity
    treatment_effect: INHIBITS
    description: >-
      Flecainide suppresses the triggered ectopic activity arising on the
      IK1-depleted substrate, although its net effect is variant-dependent and
      may be proarrhythmic for some Kir2.1 variants.
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Empiric treatment with flecainide should be considered for significant, frequent ventricular arrhythmias in the setting of reduced left ventricular function."
    explanation: GeneReviews endorses empiric flecainide for significant ventricular arrhythmia in ATS.
  - reference: PMID:21148745
    reference_title: "Biophysical and molecular characterization of a novel de novo KCNJ2 mutation associated with Andersen-Tawil syndrome and catecholaminergic polymorphic ventricular tachycardia mimicry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient's symptoms continued after administration of nadolol but subsided after treatment with flecainide."
    explanation: Case-level evidence of flecainide efficacy where beta-blockade failed.
  - reference: PMID:39711719
    reference_title: "Kir2.1 mutations differentially increase the risk of flecainide proarrhythmia in Andersen Tawil Syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Of 53 ATS1 patients reviewed from the literature, 54% responded partially to flecainide, with ventricular arrhythmia (VA) reduction in only 23%."
    explanation: >-
      Tempers the efficacy claim. Marked PARTIAL because this literature review
      shows only a minority achieve genuine arrhythmia reduction, and the source
      is a preprint awaiting peer review.
  - reference: PMID:39711719
    reference_title: "Kir2.1 mutations differentially increase the risk of flecainide proarrhythmia in Andersen Tawil Syndrome."
    supports: REFUTE
    evidence_source: MODEL_ORGANISM
    snippet: "Class-Ic AADs are only partially effective and might be proarrhythmic in some ATS1 patients."
    explanation: >-
      Directly challenges uniform flecainide safety in ATS1, with
      variant-dependent proarrhythmia demonstrated in cardiac-specific mouse
      models and patient-derived iPSC cardiomyocyte monolayers.
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Prevention of secondary complications: Cautious use of antiarrhythmic drugs (particularly class I drugs) that may paradoxically exacerbate the neuromuscular symptoms."
    explanation: >-
      Records the GeneReviews drug-safety warning that class I antiarrhythmics
      may worsen the skeletal-muscle arm of the disease.
- name: Beta-Blocker Therapy
  description: >-
    Beta-adrenergic blockade is widely used in inherited arrhythmia syndromes
    and is frequently prescribed in ATS on the rationale that suppressing
    adrenergic drive limits triggered activity. In the largest ATS1 outcome
    cohort, however, beta-blockers alone did not reduce the rate of
    life-threatening arrhythmic events relative to no therapy, nor did they in
    combination with class Ic antiarrhythmic drugs. Beta-blockade is therefore
    recorded here as a commonly used but unproven strategy in ATS rather than
    as an established disease-modifying therapy, and it is the comparator arm
    under formal test in the ongoing N-of-1 trial series NCT06205550.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: beta-adrenergic antagonist
      term:
        id: NCIT:C29576
        label: Beta-Adrenergic Antagonist
  target_mechanisms:
  - target: Delayed Terminal Repolarization and Triggered Activity
    treatment_effect: INHIBITS
    description: >-
      The intended mechanism is reduction of adrenergic facilitation of
      delayed afterdepolarization-driven triggered activity. Outcome data do
      not show a corresponding reduction in life-threatening arrhythmic
      events, so the mechanistic rationale should not be read as demonstrated
      clinical benefit.
  evidence:
  - reference: PMID:32299589
    reference_title: Natural History and Risk Stratification in Andersen-Tawil Syndrome Type 1.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "was not reduced by beta-blockers alone (1.37 per 100 py; p = 1.00), or in combination with Class Ic antiarrhythmic drugs (1.46 per 100 py, p = 1.00)."
    explanation: >-
      Refutes an event-reducing effect of beta-blockade, alone or added to
      class Ic therapy, in the largest reported ATS1 outcome cohort.
  - reference: clinicaltrials:NCT06205550
    reference_title: "Optimal Drug Therapy for the Suppression of Ventricular Arrhythmias in Andersen-Tawil Syndrome and Multifocal Ectopic Purkinje-related Premature Contractions: a Series of N-of-1 Trials"
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "For ATS, flecainide monotherapy will be compared with combination therapy of flecainide and a β-blocker or calcium channel blocker."
    explanation: >-
      Documents that beta-blocker add-on to flecainide remains an open question
      being tested prospectively rather than an established standard.
- name: Implantable Cardioverter-Defibrillator
  description: >-
    An implantable cardioverter-defibrillator is used for survivors of cardiac
    arrest, for tachycardia-induced syncope, and for selected patients with
    recurrent haemodynamically significant sustained ventricular tachycardia
    despite medical therapy. Frequent but tolerated ectopy alone does not
    warrant implantation.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: implantable cardioverter-defibrillator implantation
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_mechanisms:
  - target: Arrhythmic Loss of Cardiac Output
    treatment_effect: INHIBITS
    description: >-
      The device does not modify the substrate; it terminates a
      haemodynamically catastrophic rhythm before it becomes fatal.
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "implantable cardioverter-defibrillator for those with tachycardia-induced syncope"
    explanation: GeneReviews gives the indication for defibrillator implantation in ATS.
  - reference: PMID:24861851
    reference_title: "Andersen-Tawil syndrome: report of 3 novel mutations and high risk of symptomatic cardiac involvement."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "An implantable cardioverter-defibrillator was utilized in 40% of cases."
    explanation: Documents real-world defibrillator use in a molecularly confirmed ATS cohort.
- name: Avoidance of QT-Prolonging and Potassium-Wasting Agents
  description: >-
    ATS carries specific drug-safety warnings. Medications known to prolong the
    QT interval should be avoided; salbutamol inhalers may exacerbate cardiac
    arrhythmias; and thiazide and other potassium-wasting diuretics may provoke
    drug-induced hypokalaemia, precipitating paralytic attacks and aggravating
    QT prolongation. Amiodarone deserves separate emphasis: in the largest
    ATS1 outcome cohort its administration carried by far the strongest
    association with life-threatening arrhythmic events, and the authors
    conclude it is proarrhythmic and should be avoided. Because cardiac and
    skeletal muscle respond differently, a drug that helps one tissue may harm
    the other, which is the central management difficulty of the disorder.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: avoidance of contraindicated medications
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Delayed Terminal Repolarization and Triggered Activity
    treatment_effect: INHIBITS
    description: >-
      Removing QT-prolonging and potassium-wasting exposures prevents further
      loading of an already destabilized repolarization reserve.
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Agents/circumstances to avoid: Medications known to prolong QT intervals; salbutamol inhalers (may exacerbate cardiac arrhythmias); thiazide and other potassium-wasting diuretics (may provoke drug-induced hypokalemia and could aggravate the QT interval prolongation)."
    explanation: The GeneReviews Agents/Circumstances to Avoid section, recorded verbatim as the drug-safety warning for ATS.
  - reference: PMID:17395133
    reference_title: "Management and treatment of Andersen-Tawil syndrome (ATS)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Because of differences in cardiac and skeletal muscle physiology, drugs that may have a beneficial effect on cardiac function may have a detrimental effect on skeletal muscle and vice versa."
    explanation: States the cross-tissue therapeutic conflict that makes drug selection in ATS uniquely difficult.
  - reference: PMID:32299589
    reference_title: Natural History and Risk Stratification in Andersen-Tawil Syndrome Type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Amiodarone is proarrhythmic and should be avoided in patients with ATS1."
    explanation: Adds amiodarone to the ATS drug-avoidance list on the basis of cohort outcome data.
- name: Rhythm Surveillance and Cascade Testing
  description: >-
    Asymptomatic individuals with a KCNJ2 pathogenic variant undergo annual
    12-lead electrocardiography and 24-hour Holter monitoring. Relatives at
    risk are offered molecular testing if the familial variant is known, or
    detailed neurologic and cardiologic evaluation with electrocardiography and
    Holter monitoring if it is not.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: rhythm surveillance and cascade genetic testing
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Surveillance: Annual screening of asymptomatic individuals with a KCNJ2 pathogenic variant with a 12-lead EKG and 24-hour Holter monitoring."
    explanation: GeneReviews specifies the surveillance protocol for KCNJ2 variant carriers.
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Evaluation of relatives at risk: Molecular genetic testing if the pathogenic variant is known; if not, detailed neurologic and cardiologic evaluation, 12-lead EKG, and 24-hour Holter monitoring to reduce morbidity and mortality through early diagnosis and treatment of at-risk relatives."
    explanation: GeneReviews specifies cascade evaluation of at-risk relatives.
progression:
- phase: Established disease course and long-term arrhythmic risk
  notes: >-
    Quantitative natural-history data come from the largest reported ATS1
    cohort (118 patients from 57 families, 23 centres). The cumulative
    probability of a first life-threatening arrhythmic event was 7.9% at five
    years over a median 6.2-year follow-up. Evidenced predictors of such events
    are a history of unexplained syncope, documented sustained ventricular
    tachycardia, and administration of amiodarone; dysmorphic features are not
    among the reported predictors.
  evidence:
  - reference: PMID:32299589
    reference_title: Natural History and Risk Stratification in Andersen-Tawil Syndrome Type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Over a median follow-up of 6.2 years (interquartile range: 2.7 to 16.5 years), 17 patients experienced a first LAE, with a cumulative probability of 7.9% at 5 years."
    explanation: Quantifies the five-year cumulative risk of a first life-threatening arrhythmic event in molecularly defined ATS1.
  - reference: PMID:32299589
    reference_title: Natural History and Risk Stratification in Andersen-Tawil Syndrome Type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A history of unexplained syncope or of documented sustained ventricular tachycardia is associated with a higher risk of LAE."
    explanation: Identifies the two clinical predictors of life-threatening arrhythmic events, and is the source that excludes dysmorphic features from the risk model.
  - reference: PMID:32299589
    reference_title: Natural History and Risk Stratification in Andersen-Tawil Syndrome Type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Amiodarone is proarrhythmic and should be avoided in patients with ATS1."
    explanation: Identifies the third and strongest evidenced risk association, which is iatrogenic rather than constitutional.
diagnosis:
- name: Clinical and electrocardiographic diagnostic criteria
  description: >-
    ATS is diagnosed by recognizing the characteristic triad of periodic
    paralysis, ventricular arrhythmia with repolarization abnormality, and
    dysmorphic features, combined with the electrocardiographic signature. The
    diagnosis can be established on clinical and EKG grounds alone, so a
    negative molecular result does not exclude it. Because only about 60% of
    affected individuals express all three components, incomplete presentations
    still qualify when the electrocardiographic phenotype is characteristic.
  results: >-
    Characteristic clinical and EKG findings, with or without an identified
    KCNJ2 pathogenic variant, establish the diagnosis of ATS.
  diagnosis_term:
    preferred_term: clinical evaluation for the ATS triad
    term:
      id: NCIT:C124351
      label: Clinical Evaluation
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of ATS is established in an individual with characteristic clinical and EKG findings and/or identification of a pathogenic variant in KCNJ2."
    explanation: The GeneReviews DIAGNOSIS/TESTING statement, which is the authoritative diagnostic rule for ATS.
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A triad of periodic muscle paralysis, repolarization changes in the electrocardiogram, and structural body changes characterize ATS."
    explanation: Names the three clinical components that constitute the diagnostic triad.
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "About 60% of affected individuals have all features of the major triad."
    explanation: >-
      Supports the caveat that a complete triad is not required: roughly 40% of
      affected individuals present incompletely, so triad-based criteria must
      tolerate partial expression.
- name: Resting and ambulatory electrocardiography
  description: >-
    Twelve-lead electrocardiography is the core cardiac diagnostic test in
    suspected ATS. The type-1 ATS electrocardiographic phenotype comprises
    frequent premature ventricular contractions, Q-U interval prolongation,
    prominent U waves, and bidirectional ventricular tachycardia, with QT/QTc
    typically normal or only minimally prolonged. Dedicated electrocardiographic
    criteria for type-1 ATS have been proposed on this basis.
  results: >-
    Frequent resting premature ventricular contractions, QU/QUc prolongation,
    prominent U waves, and bidirectional ventricular tachycardia with a normal
    or minimally prolonged QT support type-1 ATS.
  diagnosis_term:
    preferred_term: electrocardiography
    term:
      id: NCIT:C38053
      label: Electrocardiography
  evidence:
  - reference: PMID:24827800
    reference_title: "Electrocardiogram in Andersen-Tawil syndrome. New electrocardiographic criteria for diagnosis of type-1 Andersen-Tawil syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac manifestations of ATS include frequent premature ventricular contractions (PVC), Q-U interval prolongation, prominent U-waves, and a special type of polymorphic ventricular tachycardia (PMVT) called bidirectional ventricular tachycardia (BiVT)."
    explanation: Enumerates the electrocardiographic findings that constitute the diagnostic cardiac phenotype of ATS.
  - reference: PMID:24827800
    reference_title: "Electrocardiogram in Andersen-Tawil syndrome. New electrocardiographic criteria for diagnosis of type-1 Andersen-Tawil syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The article describes the new electrocardiographic criteria proposed for diagnosis of type-1 Andersen-Tawil syndrome."
    explanation: Establishes that formal electrocardiographic diagnostic criteria exist specifically for type-1 ATS.
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Prolongation of the QU/QUc intervals and normal or minimally prolonged QT/QTc intervals with a tendency to ventricular arrhythmias are typical repolarization changes."
    explanation: >-
      Specifies that the diagnostic repolarization abnormality is QU rather
      than QT prolongation, which is why measuring QU is required and why a
      normal QTc does not exclude ATS.
- name: Ambulatory Holter rhythm monitoring
  description: >-
    Twenty-four-hour Holter monitoring complements the resting
    electrocardiogram by capturing the intermittent ectopy and bidirectional
    ventricular tachycardia that define the ATS rhythm phenotype. It is also
    the test used to evaluate at-risk relatives when the familial KCNJ2 variant
    is not known, and for annual surveillance of asymptomatic carriers.
  results: >-
    Detection of a high burden of multifocal premature ventricular contractions
    or bidirectional ventricular tachycardia on ambulatory monitoring supports
    the diagnosis and identifies affected relatives.
  diagnosis_term:
    preferred_term: Holter monitoring
    term:
      id: NCIT:C38064
      label: Holter Monitoring
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Evaluation of relatives at risk: Molecular genetic testing if the pathogenic variant is known; if not, detailed neurologic and cardiologic evaluation, 12-lead EKG, and 24-hour Holter monitoring to reduce morbidity and mortality through early diagnosis and treatment of at-risk relatives."
    explanation: GeneReviews specifies EKG plus 24-hour Holter monitoring as the diagnostic evaluation of at-risk relatives without a known variant.
- name: KCNJ2 molecular genetic testing
  description: >-
    Molecular testing of KCNJ2 (sequence analysis, with deletion/duplication
    analysis when sequencing is uninformative) confirms type-1 ATS and enables
    cascade testing of relatives. Detection rate is limited: KCNJ2 pathogenic
    variants are found in up to about 60% of clinically diagnosed patients, so
    a negative result does not exclude ATS and the clinical/EKG route to
    diagnosis remains available.
  results: >-
    Identification of a pathogenic KCNJ2 variant establishes type-1 ATS and
    permits predictive testing of relatives; a negative result leaves the
    clinical diagnosis intact.
  diagnosis_term:
    preferred_term: molecular genetic testing
    term:
      id: NCIT:C19770
      label: Molecular Analysis
  evidence:
  - reference: PMID:20301441
    reference_title: "Andersen-Tawil Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of ATS is established in an individual with characteristic clinical and EKG findings and/or identification of a pathogenic variant in KCNJ2."
    explanation: GeneReviews makes identification of a pathogenic KCNJ2 variant an alternative sufficient route to diagnosis.
  - reference: PMID:24827800
    reference_title: "Electrocardiogram in Andersen-Tawil syndrome. New electrocardiographic criteria for diagnosis of type-1 Andersen-Tawil syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "KCNJ2 mutations are detectable in up to 60 % of patients with ATS."
    explanation: Quantifies the molecular detection rate, establishing the sensitivity limit of genetic testing in ATS.
differential_diagnoses:
- name: Catecholaminergic polymorphic ventricular tachycardia
  description: >-
    CPVT shares bidirectional ventricular tachycardia with ATS and is the
    principal arrhythmic mimic. The discriminator is the resting ectopy burden
    and the trigger context: frequent premature ventricular contractions at
    rest favour ATS, whereas CPVT arrhythmia is adrenergically driven and
    emerges during or after exercise.
  disease_term:
    preferred_term: catecholaminergic polymorphic ventricular tachycardia
    term:
      id: MONDO:0017990
      label: catecholaminergic polymorphic ventricular tachycardia
  distinguishing_features:
  - Frequent premature ventricular contractions at rest favour ATS over typical CPVT
  - In CPVT, polymorphic and bidirectional ventricular tachycardia are exercise- or catecholamine-provoked rather than present at rest
  - Periodic paralysis and the dysmorphic triad are absent in CPVT
  evidence:
  - reference: PMID:24827800
    reference_title: "Electrocardiogram in Andersen-Tawil syndrome. New electrocardiographic criteria for diagnosis of type-1 Andersen-Tawil syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presence of frequent PVCs at rest are helpful in distinguishing ATS from typical catecholaminergic polymorphic ventricular tachycardia (CPVT)."
    explanation: States the resting-ectopy discriminator between ATS and CPVT.
  - reference: PMID:24827800
    reference_title: "Electrocardiogram in Andersen-Tawil syndrome. New electrocardiographic criteria for diagnosis of type-1 Andersen-Tawil syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In typical CPVT, rapid PMVT and BiVT usually manifest during or after exercising."
    explanation: Establishes the exercise-provoked trigger context that separates CPVT from ATS.
- name: Long QT syndrome
  description: >-
    ATS has historically been labelled LQT7, but the repolarization
    abnormality is QU rather than QT prolongation and the arrhythmia profile
    differs. Frequent resting premature ventricular contractions and
    asymptomatic ventricular tachycardia are characteristic of ATS and uncommon
    in long QT syndrome, whose torsade de pointes is faster and more often
    symptomatic.
  disease_term:
    preferred_term: long QT syndrome
    term:
      id: MONDO:0002442
      label: long QT syndrome
  distinguishing_features:
  - ATS prolongs QU/QUc with a normal or only minimally prolonged QT/QTc
  - Frequent resting premature ventricular contractions and asymptomatic ventricular tachycardia are typical of ATS but uncommon in LQTS
  - Periodic paralysis and the dysmorphic triad are absent in isolated LQTS
  evidence:
  - reference: PMID:24827800
    reference_title: "Electrocardiogram in Andersen-Tawil syndrome. New electrocardiographic criteria for diagnosis of type-1 Andersen-Tawil syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PVCs at rest are quite frequent in ATS1 patients, however, in LQTS patients, PVCs and asymptomatic VT are uncommon which also contributes to differentiating them."
    explanation: States the resting-ectopy discriminator between ATS1 and long QT syndrome.
  - reference: PMID:32947483
    reference_title: "Andersen-Tawil Syndrome: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Prolongation of the QU/QUc intervals and normal or minimally prolonged QT/QTc intervals with a tendency to ventricular arrhythmias are typical repolarization changes."
    explanation: >-
      Supports the interval-based discriminator: ATS prolongs QU rather than
      QT, which is why the historical LQT7 label is misleading.
clinical_trials:
- name: NCT00521794
  phase: NOT_APPLICABLE
  status: COMPLETED
  description: >-
    Completed multi-site observational natural-history study (28 participants)
    characterizing ATS, establishing whether manifestations change over time,
    and testing whether they correlate with KCNJ2 genotype. This is the
    genotype-phenotype correlation study underlying much of the longitudinal
    ATS literature; it is observational, so no trial phase applies.
  target_phenotypes:
  - preferred_term: Periodic paralysis
    term:
      id: HP:0003768
      label: Periodic paralysis
  - preferred_term: Ventricular arrhythmia
    term:
      id: HP:0004308
      label: Ventricular arrhythmia
  evidence:
  - reference: clinicaltrials:NCT00521794
    reference_title: "Andersen-Tawil Syndrome: Genotype-Phenotype Correlation and Longitudinal Study"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The purpose of this multi-site study is to better characterize ATS, establish whether symptoms change over time, and determine if symptoms are related to a mutation in the KCNJ2 gene."
    explanation: ClinicalTrials.gov documents a completed longitudinal genotype-phenotype study in ATS.
- name: NCT00839501
  phase: PHASE_I
  status: TERMINATED
  description: >-
    Interventional trial of potassium supplementation and acetazolamide,
    testing whether either affects the duration of episodic weakness and the
    cardiac rhythm abnormalities of ATS. Terminated in 2011 for inability to
    recruit a sufficient number of participants, so it produced no efficacy
    read-out. This is the reason the potassium-repletion and carbonic
    anhydrase inhibitor treatments in this entry rest on GeneReviews management
    guidance rather than on randomized evidence.
  target_phenotypes:
  - preferred_term: Episodic flaccid weakness
    term:
      id: HP:0003752
      label: Episodic flaccid weakness
  - preferred_term: Ventricular arrhythmia
    term:
      id: HP:0004308
      label: Ventricular arrhythmia
  notes: >-
    ClinicalTrials.gov records the reason for termination as inability to
    recruit a sufficient number of participants. That field is not part of the
    cached study summary, so it is recorded here as a note rather than as an
    evidence snippet.
  evidence:
  - reference: clinicaltrials:NCT00839501
    reference_title: Therapeutic Trial of Potassium and Acetazolamide in Andersen-Tawil Syndrome
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The purpose of this study is to determine whether potassium supplements and/or the medication acetazolamide affect the duration of muscle weakness and heart rhythm abnormalities in people with ATS."
    explanation: Documents the intended interventions and endpoints of the only registered therapeutic trial of the two mainstay ATS treatments.
  - reference: clinicaltrials:NCT00839501
    reference_title: Therapeutic Trial of Potassium and Acetazolamide in Andersen-Tawil Syndrome
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "The cause of some ATS cases remains unknown, and no specific treatments have been established."
    explanation: >-
      Supports the entry's position that ATS therapy is not established on
      randomized evidence; graded PARTIAL because it states the evidence gap
      rather than any treatment effect.
- name: NCT06205550
  phase: PHASE_II
  status: NOT_RECRUITING
  notes: >-
    ClinicalTrials.gov reports the overall status as "Not yet recruiting". The
    schema's trial-status enum has no NOT_YET_RECRUITING value, so
    NOT_RECRUITING is used as the nearest permissible term and the exact
    registry value is recorded here.
  description: >-
    Aggregated series of randomized, open-label N-of-1 trials in adults with
    ATS or multifocal ectopic Purkinje-related premature contractions who are
    already on flecainide. For ATS, flecainide monotherapy is compared with
    flecainide plus a beta-blocker or calcium channel blocker, with ventricular
    ectopy burden on electrocardiographic monitoring as the primary endpoint.
    Its explicit rationale is the lack of high-quality efficacy evidence for
    the therapeutic strategies currently used, which is the same gap this
    entry records around flecainide and beta-blockade.
  target_phenotypes:
  - preferred_term: Premature ventricular contractions
    term:
      id: HP:0006682
      label: Premature ventricular contraction
  - preferred_term: Bidirectional ventricular tachycardia
    term:
      id: HP:0034040
      label: Bidirectional ventricular tachycardia
  evidence:
  - reference: clinicaltrials:NCT06205550
    reference_title: "Optimal Drug Therapy for the Suppression of Ventricular Arrhythmias in Andersen-Tawil Syndrome and Multifocal Ectopic Purkinje-related Premature Contractions: a Series of N-of-1 Trials"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Objective: To investigate the efficacy of various therapeutic strategies for reducing ventricular ectopy burden in patients with ATS or MEPPC."
    explanation: States the objective of the only currently registered interventional antiarrhythmic trial in ATS.
  - reference: clinicaltrials:NCT06205550
    reference_title: "Optimal Drug Therapy for the Suppression of Ventricular Arrhythmias in Andersen-Tawil Syndrome and Multifocal Ectopic Purkinje-related Premature Contractions: a Series of N-of-1 Trials"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A number of therapeutic strategies are suggested in these conditions, but there is a lack of high-quality evidence on their efficacy."
    explanation: Documents the evidence gap that motivates the trial and that this entry records in its treatment grading.

📚

References & Deep Research

References

1

PMID:20301441

Andersen-Tawil Syndrome.

No top-level findings curated for this source.

Deep Research

1

Falcon ▸

Disease Characteristics Research Template

Edison Scientific Literature 12 citations 2026-07-31T17:35:37.852334

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Characteristics Research Template

Target Disease

Disease Name: Andersen-Tawil Syndrome
MONDO ID: (if available)
Category: Genetic

Research Objectives

Please provide a comprehensive research report on Andersen-Tawil Syndrome covering all of the disease characteristics listed below. This report will be used to populate a disease knowledge base entry. Be thorough and cite primary literature (PMID preferred) for all claims.

For each section, suggested databases/resources are listed. These are the first places you should search for information on each topic.

1. Disease Information

Search first: OMIM, Orphanet, ICD-10/ICD-11, MeSH, PubMed

What is the disease? Provide a concise overview.
What are the key identifiers? (OMIM, Orphanet, ICD-10/ICD-11, MeSH, Mondo)
What are the common synonyms and alternative names?
Is the information derived from individual patients (e.g., EHR) or aggregated disease-level resources?

2. Etiology

Disease Causal Factors: What are the primary causes? (genetic, environmental, infectious, mechanistic)
Risk Factors:

Search first: PubMed, Cochrane Library, UpToDate, clinical guidelines, ClinVar, ClinGen, GWAS Catalog, PheGenI, CTD, CDC, WHO, epidemiological databases
Genetic risk factors (causal variants, susceptibility loci, modifier genes)
Environmental risk factors (toxins, lifestyle, occupational exposures, age, sex, family history)
Protective Factors:

Search first: PubMed, Cochrane Library, clinical trial databases, GWAS Catalog, gnomAD, WHO, CDC, nutrition databases
Genetic protective factors (protective variants, modifier alleles)
Environmental protective factors (diet, lifestyle, exposures that reduce risk)
Gene-Environment Interactions: How do genetic and environmental factors interact to influence disease?

Search first: CTD, PubMed, PheGenI, GxE databases

3. Phenotypes

Search first: HPO (Human Phenotype Ontology), OMIM, Orphanet, PubMed, clinicaltrials.gov, MedDRA, SNOMED CT, DECIPHER, LOINC

For each phenotype, provide: - Phenotype type: symptoms, clinical signs, physical manifestations, behavioral changes, or laboratory abnormalities

For symptoms/signs: HPO, OMIM, Orphanet, PubMed For behavioral changes: HPO, DSM, RDoC (Research Domain Criteria), PubMed For laboratory abnormalities: LOINC, SNOMED CT, LabTests Online, PubMed - Phenotype characteristics: Search first: OMIM, Orphanet, HPO, PubMed - Age of symptom onset (neonatal, childhood, adult-onset, late-onset) - Symptom severity (mild, moderate, severe, variable) - Symptom progression (stable, progressive, episodic, fluctuating) - Frequency among affected individuals (percentage or qualitative) - Quality of life impact: Effects on daily functioning and well-being (per-phenotype when possible) Search first: EQ-5D database, SF-36, WHO QOL databases, PubMed - Suggest HPO (Human Phenotype Ontology) terms for each phenotype

4. Genetic/Molecular Information

Causal Genes: Gene mutations or chromosomal abnormalities responsible for disease (gene symbols, OMIM IDs)

Search first: OMIM, ClinVar, HGMD, Ensembl, NCBI Gene
Pathogenic Variants:
Affected genes (gene symbols, HGNC IDs) > Search first: OMIM, NCBI Gene, Ensembl, HGNC, UniProt, GeneCards
Variant classification (pathogenic, likely pathogenic, VUS per ACMG/AMP guidelines) > Search first: ClinVar, ClinGen, ACMG/AMP guidelines, VarSome
Variant type/class (missense, frameshift, nonsense, splice-site, structural)
Allele frequency in population databases > Search first: gnomAD, 1000 Genomes, ExAC, TOPMed, dbSNP
Somatic vs germline origin > Search first: COSMIC (somatic), ClinVar, ICGC, TCGA
Functional consequences (loss of function, gain of function, dominant negative)
Modifier Genes: Genes that modify disease severity or expression
Epigenetic Information: DNA methylation, histone modifications, chromatin changes affecting disease

Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth
Chromosomal Abnormalities: Large-scale genetic changes (aneuploidy, translocations, inversions)

Search first: DECIPHER, ClinVar, ECARUCA, UCSC Genome Browser

5. Environmental Information

Environmental Factors: Non-genetic contributing factors (toxins, radiation, pollution, occupational exposure)

Search first: CTD (Comparative Toxicogenomics Database), TOXNET, PubMed, EPA databases
Lifestyle Factors: Behavioral factors (smoking, diet, exercise, alcohol consumption)

Search first: CDC databases, WHO, PubMed, NHANES
Infectious Agents: If applicable, pathogens causing or triggering disease (bacteria, viruses, fungi, parasites)

Search first: NCBI Taxonomy, ViPR, BV-BRC, MicrobeDB, GIDEON

6. Mechanism / Pathophysiology

Molecular Pathways: Specific signaling cascades or biochemical pathways involved (Wnt, MAPK, mTOR, PI3K-AKT, etc.)

Search first: KEGG, Reactome, WikiPathways, PathBank, BioCyc
Cellular Processes: Cell-level mechanisms (apoptosis, autophagy, cell cycle dysregulation, inflammation, etc.)

Search first: Gene Ontology (GO), Reactome, KEGG, PubMed
Protein Dysfunction: How protein structure or function is altered (misfolding, aggregation, loss of function, gain of function)

Search first: UniProt, PDB (Protein Data Bank), InterPro, Pfam, AlphaFold
Metabolic Changes: Alterations in metabolic processes (energy metabolism, lipid metabolism, amino acid metabolism)

Search first: KEGG, BioCyc, HMDB (Human Metabolome Database), BRENDA
Immune System Involvement: Role of immune response (autoimmunity, immunodeficiency, chronic inflammation)

Search first: ImmPort, Immunome Database, IEDB, Gene Ontology
Tissue Damage Mechanisms: How tissues/ are injured (oxidative stress, ischemia, fibrosis, necrosis)

Search first: PubMed, Gene Ontology, Reactome
Biochemical Abnormalities: Specific molecular defects (enzyme deficiencies, receptor dysfunction, ion channel defects)

Search first: BRENDA, UniProt, KEGG, OMIM, PubMed
Epigenetic Changes: DNA methylation, histone modifications affecting gene expression in disease

Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth
Molecular Profiling (if available):
Transcriptomics/gene expression changes > Search first: GEO (Gene Expression Omnibus), ArrayExpress, GTEx, Human Cell Atlas, SRA
Proteomics findings > Search first: PRIDE, ProteomeXchange, Human Protein Atlas, STRING, BioGRID
Metabolomics signatures > Search first: MetaboLights, Metabolomics Workbench, HMDB, METLIN
Lipidomics alterations > Search first: LIPID MAPS, SwissLipids, LipidHome, Metabolomics Workbench
Genomic structural features > Search first: UCSC Genome Browser, Ensembl, NCBI, dbVar, DGV
Advanced Technologies (if applicable):
Single-cell analysis findings (cell-type specific mechanisms, cellular heterogeneity) > Search first: Human Cell Atlas, Single Cell Portal, GEO, CELLxGENE
Spatial transcriptomics findings > Search first: GEO, Spatial Research, Vizgen, 10x Genomics data
Multi-omics integration results > Search first: TCGA, ICGC, cBioPortal, LinkedOmics, PubMed
Functional genomics screens (CRISPR, RNAi) > Search first: DepMap, GenomeRNAi, PubMed, BioGRID ORCS

For each mechanism, describe: - The causal chain from initial trigger to clinical manifestation - Which mechanisms are upstream vs downstream - What cell types and biological processes are involved - Suggest GO terms for biological processes and CL terms for cell types

7. Anatomical Structures Affected

Organ Level:
Primary organs directly affected
Secondary organ involvement (complications, secondary effects)
Body systems involved (cardiovascular, nervous, digestive, respiratory, endocrine, etc.)

Search first: Uberon, FMA (Foundational Model of Anatomy), OMIM, HPO, ICD-11, MeSH, SNOMED CT
Tissue and Cell Level:
Specific tissue types affected (epithelial, connective, muscle, nervous)
Specific cell populations targeted (with Cell Ontology terms)

Search first: Uberon, Human Protein Atlas, Cell Ontology, Human Cell Atlas, CellMarker, PanglaoDB
Subcellular Level:
Cellular compartments involved (mitochondria, nucleus, ER, lysosomes) (with GO Cellular Component terms)

Search first: Gene Ontology (Cellular Component), UniProt, Human Protein Atlas
Localization:
Specific anatomical sites (with UBERON terms) > Search first: FMA, Uberon, NeuroNames (for brain), SNOMED CT
Lateralization (unilateral, bilateral, asymmetric) > Search first: HPO, clinical literature, imaging databases

8. Temporal Development

Onset:
Typical age of onset (congenital, pediatric, adult, geriatric)
Onset pattern (acute, subacute, chronic, insidious)

Search first: OMIM, Orphanet, HPO, PubMed
Progression:
Disease stages (early, intermediate, advanced, end-stage) > Search first: Cancer Staging Manual (AJCC), WHO classifications, PubMed
Progression rate (rapid, slow, variable)
Disease course pattern (episodic, relapsing-remitting, progressive, stable)
Disease duration (self-limited, chronic lifelong)

Search first: Disease registries, longitudinal cohort databases, natural history studies, PubMed, Orphanet, OMIM
Patterns:
Remission patterns (spontaneous, treatment-induced) > Search first: Clinical trial databases, disease registries, PubMed
Critical periods (time windows of vulnerability or opportunity for intervention) > Search first: PubMed, developmental biology databases, clinical guidelines

9. Inheritance and Population

Epidemiology:
Prevalence (cases per 100,000 at given time)
Incidence (new cases per 100,000 per year)

Search first: Orphanet, CDC, WHO, GBD (Global Burden of Disease), national registries, SEER, disease registries
For Genetic Etiology:
Inheritance pattern (AD, AR, X-linked, mitochondrial, multifactorial, polygenic) > Search first: OMIM, Orphanet, ClinVar, GTR (Genetic Testing Registry)
Penetrance (complete, incomplete, age-dependent) > Search first: ClinVar, OMIM, PubMed, ClinGen
Expressivity (variable, consistent) > Search first: OMIM, ClinVar, PubMed
Genetic anticipation (increasing severity in successive generations) > Search first: OMIM, PubMed (especially for repeat expansion disorders)
Germline mosaicism > Search first: ClinVar, OMIM, genetic counseling literature, PubMed
Founder effects (population-specific mutations) > Search first: gnomAD, population genetics databases, PubMed
Consanguinity role > Search first: OMIM, population studies, genetic counseling resources
Carrier frequency > Search first: gnomAD, carrier screening databases, GeneReviews, GTR
Population Demographics:
Affected populations (ethnic or demographic groups with higher prevalence) > Search first: gnomAD, 1000 Genomes, PAGE Study, PubMed, population registries
Geographic distribution (endemic areas, regional variation) > Search first: WHO, CDC, GBD, Orphanet, geographic epidemiology databases
Geographic distribution of specific variants
Sex ratio (male:female) > Search first: Disease registries, OMIM, PubMed, epidemiological databases
Age distribution of affected individuals > Search first: CDC, disease registries, SEER, Orphanet

10. Diagnostics

Clinical Tests:
Laboratory tests (blood, urine, tissue chemistry, specific enzyme assays) > Search first: LOINC, LabTests Online, PubMed
Biomarkers (proteins, metabolites, genetic markers, circulating biomarkers) > Search first: FDA Biomarker List, BEST (Biomarkers, EndpointS, and other Tools), PubMed
Imaging studies (X-ray, CT, MRI, PET, ultrasound) > Search first: RadLex, DICOM, Radiopaedia, imaging databases
Functional tests (pulmonary function, cardiac stress tests) > Search first: LOINC, clinical guidelines, PubMed
Electrophysiology (EEG, EMG, ECG, nerve conduction studies) > Search first: LOINC, clinical neurophysiology databases, PubMed
Biopsy findings (histopathology, immunohistochemistry) > Search first: SNOMED CT, College of American Pathologists resources, PubMed
Pathology findings (microscopic examination) > Search first: SNOMED CT, Digital Pathology databases, PubMed
Genetic Testing:

Search first: GTR (Genetic Testing Registry), GeneReviews, ClinGen
Overview of recommended genetic testing approach
Whole genome sequencing (WGS) utility > Search first: GTR, ClinVar, GEL (Genomics England), gnomAD
Whole exome sequencing (WES) utility > Search first: GTR, ClinVar, OMIM, GeneMatcher
Gene panels (which panels, which genes) > Search first: GTR, ClinVar, laboratory-specific databases
Single gene testing > Search first: GTR, ClinVar, OMIM, GeneReviews
Chromosomal microarray (CMA) > Search first: DECIPHER, ClinVar, dbVar, ECARUCA
Karyotyping > Search first: Chromosome Abnormality Database, ClinVar, cytogenetics resources
FISH > Search first: ClinVar, cytogenetics databases, PubMed
Mitochondrial DNA testing > Search first: MITOMAP, MSeqDR, ClinVar, GTR
Repeat expansion testing > Search first: GTR, ClinVar, repeat expansion databases, PubMed
Omics-Based Diagnostics (if applicable):
RNA sequencing / transcriptomics > Search first: GEO, ArrayExpress, GTEx, RNA-seq databases
Proteomics > Search first: PRIDE, ProteomeXchange, FDA Biomarker database
Metabolomics > Search first: MetaboLights, Metabolomics Workbench, HMDB
Epigenomics > Search first: GEO, ENCODE, Roadmap Epigenomics, MethBase
Liquid biopsy > Search first: COSMIC, ClinVar, liquid biopsy databases, PubMed
Clinical Criteria:
Standardized diagnostic criteria (DSM, ICD, society guidelines) > Search first: DSM-5, ICD-11, clinical society guidelines, UpToDate
Differential diagnosis (other conditions to rule out, with distinguishing features) > Search first: DynaMed, UpToDate, clinical decision support systems
Screening:
Screening methods for asymptomatic individuals (newborn screening, carrier screening, cascade screening) > Search first: ACMG recommendations, CDC newborn screening, GTR

11. Outcome/Prognosis

Survival and Mortality:
Survival rate (5-year, 10-year, overall) > Search first: SEER, cancer registries, disease-specific registries, PubMed
Life expectancy (with and without treatment if applicable) > Search first: Orphanet, disease registries, actuarial databases, PubMed
Mortality rate > Search first: CDC, WHO, GBD, national mortality databases
Disease-specific mortality (deaths directly attributable to disease) > Search first: Disease registries, CDC Wonder, GBD, PubMed
Morbidity and Function:
Morbidity (disease-related disability and health impacts) > Search first: GBD, WHO, disability databases, PubMed
Disability outcomes (long-term functional impairments) > Search first: ICF (International Classification of Functioning), disability registries
Quality of life measures (EQ-5D, SF-36, PROMIS, disease-specific tools) > Search first: EQ-5D database, SF-36, PROMIS, PubMed
Disease Course:
Complications (secondary problems: infections, organ failure, etc.) > Search first: ICD codes, disease registries, clinical databases, PubMed
Recovery potential (likelihood and extent of recovery, with vs without treatment) > Search first: Natural history studies, rehabilitation databases, PubMed
Prediction:
Prognostic factors (age, disease severity, biomarkers, treatment response) > Search first: Prognostic models databases, clinical calculators, PubMed
Prognostic biomarkers (molecular markers predicting disease course) > Search first: FDA Biomarker database, PubMed, cancer prognostic databases

12. Treatment

Pharmacotherapy:
Pharmacological treatments (drug names, drug classes, mechanisms of action) > Search first: DrugBank, RxNorm, ATC classification, DailyMed, FDA databases
Pharmacogenomics (how genetic variants affect drug metabolism, efficacy, toxicity) > Search first: PharmGKB, CPIC (Clinical Pharmacogenetics), FDA Table of PGx Biomarkers
Advanced Therapeutics:
Gene therapy (viral vectors, CRISPR, gene replacement, gene editing) > Search first: ClinicalTrials.gov, FDA gene therapy database, ASGCT resources
Cell therapy (stem cell transplant, CAR-T, cellular therapeutics) > Search first: ClinicalTrials.gov, FDA cell therapy database, FACT standards
RNA-based therapies (ASOs, siRNA, mRNA therapies) > Search first: ClinicalTrials.gov, FDA approvals, PubMed
Targeted therapies (treatments directed at specific molecular targets) > Search first: My Cancer Genome, OncoKB, ClinicalTrials.gov, FDA approvals
Immunotherapies (checkpoint inhibitors, monoclonal antibodies) > Search first: Cancer Immunotherapy Database, FDA approvals, ClinicalTrials.gov
Surgical and Interventional:
Surgical interventions (types of surgery, timing, outcomes) > Search first: CPT codes, surgical registries, clinical guidelines, PubMed
Supportive and Rehabilitative:
Supportive care (symptom management, pain control, nutrition) > Search first: Clinical guidelines, Cochrane Library, PubMed
Rehabilitation (physical therapy, occupational therapy, speech therapy) > Search first: Rehabilitation medicine databases, clinical guidelines, PubMed
Experimental:
Experimental treatments in clinical trials (with NCT identifiers if available) > Search first: ClinicalTrials.gov, EU Clinical Trials Register, WHO ICTRP
Treatment Outcomes:
Treatment response rates > Search first: Clinical trial databases, FDA reviews, systematic reviews, PubMed
Side effects and adverse events > Search first: FDA Adverse Event Reporting System (FAERS), MedWatch, PubMed
Treatment Strategy:
Treatment algorithms (clinical pathways, decision trees) > Search first: Clinical practice guidelines, NCCN Guidelines, UpToDate
Combination therapies > Search first: ClinicalTrials.gov, treatment guidelines, PubMed
Personalized medicine approaches (genotype-guided treatment) > Search first: My Cancer Genome, CIViC, PharmGKB, precision medicine databases

For each treatment, suggest NCIT (NCI Thesaurus) clinical-intervention terms where applicable.

13. Prevention

Prevention Levels:
Primary prevention (preventing disease occurrence: vaccination, risk factor modification) > Search first: CDC, WHO, USPSTF recommendations, Cochrane Library
Secondary prevention (early detection and treatment: screening programs, early intervention) > Search first: USPSTF, CDC screening guidelines, WHO
Tertiary prevention (preventing complications in those with disease) > Search first: Clinical guidelines, disease management protocols, PubMed
Immunization: Vaccine strategies (if applicable)

Search first: CDC vaccine schedules, WHO immunization, FDA vaccine database
Screening and Early Detection:
Screening programs (population-based: newborn screening, cancer screening) > Search first: CDC screening programs, USPSTF, cancer screening databases
Genetic screening (carrier screening, preimplantation genetic diagnosis, prenatal testing) > Search first: ACMG recommendations, ACOG guidelines, GTR
Risk stratification (identifying high-risk individuals for targeted prevention) > Search first: Risk prediction models, clinical calculators, PubMed
Behavioral Interventions: Lifestyle modifications to reduce risk

Search first: CDC, WHO, behavioral intervention databases, Cochrane Library
Counseling: Genetic counseling (risk assessment, family planning guidance)

Search first: NSGC resources, ACMG guidelines, GeneReviews
Public Health:
Public health interventions (sanitation, vector control, health education) > Search first: CDC, WHO, public health databases, PubMed
Environmental interventions (reducing environmental risk factors) > Search first: EPA databases, WHO environmental health, PubMed
Prophylaxis: Preventive medications or procedures

Search first: Clinical guidelines, FDA approvals, PubMed

14. Other Species / Natural Disease

Taxonomy: Species affected (with NCBI Taxon identifiers)

Search first: NCBI Taxonomy
Breed: Specific breeds affected (with VBO identifiers if applicable)

Search first: VBO (Vertebrate Breed Ontology)
Gene: Orthologous genes in other species (with NCBI Gene IDs)

Search first: NCBI Gene
Natural Disease:
Naturally occurring disease in other species (companion animals, wildlife) > Search first: OMIA (Online Mendelian Inheritance in Animals), VetCompass, PubMed
Veterinary relevance and importance in animal health > Search first: OMIA, veterinary databases, PubMed
Comparative Biology:
Comparative pathology (similarities and differences across species) > Search first: OMIA, comparative pathology databases, PubMed
Evolutionary conservation of disease mechanisms > Search first: HomoloGene, OrthoMCL, Alliance of Genome Resources
Transmission (if applicable):
Zoonotic potential > Search first: CDC zoonotic diseases, WHO zoonoses, GIDEON
Cross-species susceptibility > Search first: NCBI Taxonomy, veterinary databases, PubMed

15. Model Organisms

Model Types:
Model organism type (mammalian, invertebrate, cellular, in vitro) > Search first: Alliance of Genome Resources, model organism databases
Specific model systems (mouse, rat, zebrafish, Drosophila, C. elegans, yeast, cell lines, organoids, iPSCs) > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, SGD, ATCC, Cellosaurus
Induced models (drug treatment, surgical intervention, environmental manipulation) > Search first: MGI, model organism databases, PubMed
Genetic Models:
Types available (knockout, knock-in, transgenic, conditional, humanized) > Search first: MGI, IMPC, KOMP, EuMMCR, IMSR
Model Characteristics:
Phenotype recapitulation (how well model reproduces human disease features) > Search first: Model organism databases, comparative studies, PubMed
Model limitations (aspects of human disease not captured) > Search first: Model organism databases, PubMed, review articles
Applications:
Research applications (what aspects of disease can be studied) > Search first: Model organism databases, PubMed
Resources:
Model databases > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, IMSR, EMMA, MMRRC

Citation Requirements

Cite primary literature (PMID preferred) for all mechanistic and clinical claims
Prioritize recent reviews and landmark papers
Include direct quotes from abstracts where possible to support key statements
Distinguish evidence source types: human clinical, model organism, in vitro, computational

Output Format

Structure your response as a comprehensive narrative organized by the sections above. For each section, provide: - Factual content with specific details (numbers, percentages, gene names, variant nomenclature) - Ontology term suggestions (HPO, GO, CL, UBERON, CHEBI, NCIT, MONDO) where applicable - Evidence citations with PMIDs - Direct quotes from abstracts to support key claims - Clear indication when information is not available or not applicable for this disease

This report will be used to populate a disease knowledge base entry with: - Pathophysiology descriptions with causal chains - Gene/protein annotations (HGNC, GO terms) - Phenotype associations (HP terms) with frequencies - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Treatment annotations (NCIT terms) - Evidence items with PMIDs and exact abstract quotes - Epidemiology, prognosis, diagnostic, and prevention information - Animal model descriptions with phenotype recapitulation details

Andersen–Tawil syndrome: disease-characteristics research report

Scope and evidence note. This report synthesizes disease-level resources, human cohorts, primary functional studies, clinical-trial records, and recent 2023–2024 work. Andersen–Tawil syndrome (ATS) is exceptionally rare, so most treatment evidence is observational, from small cohorts or case reports rather than randomized trials. The December 2024 flecainide study discussed below is a preprint, not yet peer reviewed in the retrieved record.

Executive summary

ATS is a multisystem, usually autosomal-dominant ion-channel disorder defined by a variably expressed triad of: (1) ventricular arrhythmias with characteristic prominent U waves, (2) potassium-sensitive episodic paralysis, and (3) developmental craniofacial, dental, and limb abnormalities. Most molecularly confirmed disease is caused by heterozygous loss-of-function variants in KCNJ2, encoding the Kir2.1 inward-rectifier potassium channel. Reduced IK1 destabilizes resting membrane potential and terminal repolarization in cardiomyocytes and skeletal myofibers, explaining ventricular ectopy and impaired muscle excitability. Prevalence is commonly estimated near 1 per million, although underdiagnosis is likely. Ventricular arrhythmias occur in approximately 60–90%, while severe cardiac events remain much less common than ectopy but are clinically consequential; a recent review reported a 5-year cumulative sudden-cardiac-death probability of 7.9%. (pupaza2023assessmentofsudden pages 9-11, OpenTargets Search: Andersen-Tawil syndrome-KCNJ2)

Domain	Established finding	Quantitative evidence	Evidence type / source / date	Knowledge-base ontology suggestions
Definition / triad	Andersen-Tawil syndrome (ATS) is a rare inherited ion-channel disorder classically defined by ventricular arrhythmias, episodic weakness/periodic paralysis, and characteristic dysmorphic features.	Prevalence commonly cited as ~1 per 1,000,000; symptom onset within first 2 decades in 42.3%; ventricular arrhythmias in 60–90%; polymorphic VT 48%; bidirectional VT 44%.	Peer-reviewed review, Diagnostics (Nov 2023) (pupaza2023assessmentofsudden pages 9-11)	MONDO: Andersen-Tawil syndrome; HPO: Cardiac arrhythmia, Periodic paralysis, Facial dysmorphism
Genetics / KCNJ2 / Kir2.1	ATS1 is caused predominantly by heterozygous loss-of-function variants in KCNJ2, encoding inward rectifier potassium channel Kir2.1; disease is usually autosomal dominant, with sporadic/de novo cases also reported.	Open Targets disease-target association score 0.8407 for KCNJ2–ATS; 5 supporting evidence items; KCNJ2 mutations account for majority of ATS1 and ~60% of ATS overall in older primary studies.	Database evidence, Open Targets / MONDO_0008222; peer-reviewed primary study, Circ Cardiovasc Genet (Feb 2011); review, Diagnostics (Nov 2023) (OpenTargets Search: Andersen-Tawil syndrome-KCNJ2, barajasmartinez2011biophysicalandmolecular pages 7-8, pupaza2023assessmentofsudden pages 9-11)	HGNC: KCNJ2; protein: Kir2.1; GO: inward rectifier potassium channel activity; GO: regulation of membrane potential
Variant spectrum	Numerous pathogenic KCNJ2 variants are distributed throughout Kir2.1; dominant-negative effects and trafficking defects are established mechanisms for some variants.	“More than 90 mutations” summarized in 2024 preprint; historical literature cited >40 mutations by 2015 cohort report; example de novo R260P showed strong dominant-negative effect.	Preprint, medRxiv (Dec 2024); peer-reviewed cohort, Muscle & Nerve (Feb 2015); peer-reviewed primary study, Circ Cardiovasc Genet (Feb 2011) (cruz2024kir2.1mutationsdifferentially pages 3-6, kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5, barajasmartinez2011biophysicalandmolecular pages 7-8)	Sequence variant classes: missense, in-frame deletion; SO terms for missense variant / inframe deletion
Cardiac phenotype	Cardiac manifestations include PVCs, ventricular ectopy, prolonged QT/QU intervals with prominent U waves, polymorphic and bidirectional VT, and occasional cardiac arrest/SCD.	In one 15-patient cohort: ventricular arrhythmias 75%, BVT in 6/12 Holters, normal QTc in 76%, prominent U waves in 84%; 37 cardiac arrests in 259-patient meta-analysis.	Peer-reviewed cohort, Muscle & Nerve (Feb 2015); peer-reviewed meta-analysis (Jan 2026) (kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5, garcia2026genderspecificcardiacfeatures pages 1-2)	HPO: Premature ventricular contractions, Bidirectional ventricular tachycardia, Syncope, Abnormal U wave, Long QT interval
Periodic paralysis	Episodic muscle weakness is a core but variably penetrant feature; attacks may be potassium-sensitive and show sex-related variability.	In 15-patient cohort, PP observed in 7 patients across 6 kinships; attacks reported in 20% of females vs 80% of males in that series; females less likely to present with PP in 259-patient meta-analysis (p=0.02).	Peer-reviewed cohort, Muscle & Nerve (Feb 2015); peer-reviewed meta-analysis (Jan 2026) (kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5, garcia2026genderspecificcardiacfeatures pages 1-2)	HPO: Periodic paralysis, Episodic weakness, Hypokalemia (when present)
Dysmorphism	Developmental/craniofacial and limb anomalies are common and aid recognition.	In 15-patient cohort, dysmorphic features noted in 100%; study protocol lists low-set ears, hypertelorism, micrognathia, clinodactyly, syndactyly, hand/foot micromelia as diagnostic features.	Peer-reviewed cohort, Muscle & Nerve (Feb 2015); ClinicalTrials.gov observational study description (2007) (kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5, NCT00521794 chunk 1)	HPO: Hypertelorism, Micrognathia, Clinodactyly, Syndactyly, Low-set ears
Diagnostics	Practical diagnosis relies on recognition of at least 2 of 3 domains: episodic weakness, cardiac conduction/ventricular arrhythmia findings, and dysmorphic features; ECG/Holter and molecular confirmation are key.	Trial protocol diagnostic rule: ≥2 of 3 features; observational natural-history study enrolled 28 participants across 7 sites for standardized longitudinal phenotyping.	ClinicalTrials.gov observational study NCT00521794, completed; supporting clinical review 2023 (NCT00521794 chunk 1, pupaza2023assessmentofsudden pages 9-11)	HPO set above; LOINC/ECG concepts: QTc prolongation, ventricular ectopy; NCIT: genetic testing
Mechanism / pathophysiology	Reduced IK1 from dysfunctional Kir2.1 destabilizes resting membrane potential and repolarization, promoting ventricular ectopy and arrhythmia; some variants also alter sodium current/channelosome behavior.	2024 preprint reports mutation-specific reductions in IK1 and differential effects on INa with increased ventricular arrhythmia inducibility in multiple mouse models; 2011 R260P study showed trafficking defect with markedly reduced IK1.	Preprint, medRxiv (Dec 2024); peer-reviewed primary study, Circ Cardiovasc Genet (Feb 2011); peer-reviewed review, Naunyn Schmiedebergs Arch Pharmacol (Apr 2024) (cruz2024kir2.1mutationsdifferentially pages 3-6, barajasmartinez2011biophysicalandmolecular pages 7-8, cruz2024kir2.1mutationsdifferentially pages 22-24)	GO: cardiac muscle cell action potential, membrane repolarization, potassium ion transmembrane transport; CL: cardiomyocyte
Treatments / arrhythmia management	Management is individualized; beta-blockers are commonly used, flecainide may reduce arrhythmia burden in some patients, ICD is used in high-risk cases, and class-Ic safety is under active reassessment.	In 15-patient cohort, all arrhythmic patients received beta-blockers and 40% received ICDs; 2024 preprint literature review of 53 ATS1 patients found 54% partial flecainide response, VA reduction in 23%, ineffectiveness in 23%, non-fatal cardiac arrest in 13.5%.	Peer-reviewed cohort, Muscle & Nerve (Feb 2015); preprint, medRxiv (Dec 2024) (kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5, cruz2024kir2.1mutationsdifferentially pages 20-22)	NCIT: Beta-Adrenergic Receptor Blocker Therapy, Flecainide, Implantable Cardioverter-Defibrillator
Prognosis / risk	Most patients have chronic morbidity; life-threatening arrhythmias occur in a minority but are clinically important, with sex differences emerging in newer syntheses.	5-year cumulative SCD probability reported as 7.9%; risk factors summarized in 2023 review include syncope, sustained VT, amiodarone use, micrognathia, periodic paralysis, prolonged Tpeak-Tend; females had higher cardiac arrest risk in 2026 meta-analysis (p=0.02).	Peer-reviewed review, Diagnostics (Nov 2023); peer-reviewed meta-analysis (Jan 2026) (pupaza2023assessmentofsudden pages 9-11, garcia2026genderspecificcardiacfeatures pages 1-2)	HPO: Sudden cardiac death, Syncope; prognostic annotation: sustained VT history
2024 hiPSC multi-omics	A 2024 hiPSC-CM disease model combined RNA-seq and ATAC-seq to identify developmental and electrophysiologic ATS mechanisms beyond the primary channel defect.	Mutant iPSC-CMs had lower spontaneous pulsation, prolonged APD, reduced Kir2.1 current; ZNF528 was continuously downregulated from day 4; 7 potassium-related pathways downregulated (p<0.05); KCNJ2, CTTN, ATP1B1 were consistently downregulated targets.	Peer-reviewed primary study, Journal of Translational Medicine (Mar 2024) (chen2024transcriptomeandopen pages 1-3, chen2024transcriptomeandopen pages 3-4)	GO: potassium ion import/inward rectifier activity pathways; gene entities: ZNF528, CTTN, ATP1B1; CL: induced pluripotent stem cell-derived cardiomyocyte
2024 flecainide precision-safety study	Mutation-specific flecainide safety/efficacy is a major 2024 development; some KCNJ2 variants may confer proarrhythmic risk under class-Ic therapy.	In reviewed 53 ATS1 patients: partial response 54%; VA reduction only 23%; persistent VA in 20–50% of responders; non-fatal cardiac arrest 13.5%; mouse/iPSC models showed increased rotor incidence or inducibility for several variants, while S136F appeared milder.	Preprint primary/translational study, medRxiv (Dec 2024) — not peer reviewed at time cited (cruz2024kir2.1mutationsdifferentially pages 20-22, cruz2024kir2.1mutationsdifferentially pages 3-6)	NCIT: Flecainide; variant-level drug response annotation; GO: conduction velocity / arrhythmogenesis
Clinical trials	ATS-specific interventional evidence remains sparse; available studies focus on natural history and exploratory therapy.	NCT00521794 observational natural-history study: completed, n=28; NCT00839501 potassium + acetazolamide trial: terminated, phase 1, n=3; NCT06205550 N-of-1 in ATS and MEPPC: not yet recruiting, phase 2, planned n=10.	ClinicalTrials.gov records (2007 onward) (NCT00521794 chunk 1)	NCIT: Potassium, Acetazolamide; study-design metadata; evidence-source tag: clinical trial registry

Table: This table summarizes the most actionable evidence domains for Andersen-Tawil syndrome, including established findings, quantitative support, evidence provenance, and ontology-oriented mapping suggestions. It distinguishes peer-reviewed evidence from the 2024 flecainide preprint and highlights current trial activity.

1. Disease information

Definition and identifiers

Preferred name: Andersen–Tawil syndrome.
MONDO: MONDO:0008222.
OMIM: commonly represented as Andersen syndrome, 170390; the KCNJ2-associated subtype is often termed ATS type 1.
Orphanet: ORPHA:37553, “cardiodysrhythmic potassium-sensitive periodic paralysis.”
Gene: KCNJ2, Ensembl ENSG00000123700, encoding potassium inwardly rectifying channel subfamily J member 2/Kir2.1. Open Targets identifies KCNJ2 as the sole high-confidence associated target in its ATS record, supported by five evidence items and an association score of 0.8407. (OpenTargets Search: Andersen-Tawil syndrome-KCNJ2)
ICD: ATS generally lacks a uniquely specific ICD-10-CM code and may be coded under periodic paralysis, long-QT/other cardiac arrhythmia, or congenital-malformation categories depending on manifestation. ICD-11 should likewise be verified against the jurisdictional release rather than inferred from the historical label “LQT7.”
Synonyms: Andersen syndrome; Andersen–Tawil syndrome type 1; cardiodysrhythmic potassium-sensitive periodic paralysis; potassium-sensitive periodic paralysis with ventricular dysrhythmia; long-QT syndrome type 7/LQT7. “LQT7” is historically used but can mislead because many patients have a normal QTc and instead exhibit prolonged terminal repolarization/QU and prominent U waves.

The evidence is principally aggregated disease-level evidence, not EHR-derived individual-patient data. Some frequency estimates derive from assembled case reports and small cohorts and therefore are susceptible to referral and publication bias.

2. Etiology, risk, protection, and gene–environment interaction

Causal factors

The established cause of ATS1 is a germline heterozygous loss-of-function KCNJ2 variant. Inheritance is usually autosomal dominant, but de novo/sporadic cases occur. Older functional studies estimated KCNJ2 variants in about 60% of clinically diagnosed cases; KCNJ2-negative patients remain genetically heterogeneous or unresolved and are sometimes termed ATS2, although this is a clinical category rather than a single established locus. (pupaza2023assessmentofsudden pages 9-11, barajasmartinez2011biophysicalandmolecular pages 7-8)

No infectious, toxic, occupational, inflammatory, or lifestyle exposure is an established primary cause. Physiologic exposures instead act as attack triggers on the inherited electrical substrate: rest after exertion, prolonged rest, fasting, carbohydrate-rich meals, cold, emotional stress, and shifts in serum potassium may precipitate weakness or arrhythmia. A 2024 patient-derived model originated from a woman whose weakness was triggered by exercise and cold, illustrating this interaction but not proving population-wide trigger frequencies. (chen2024transcriptomeandopen pages 3-4)

Risk and protective factors

Genetic risk: a pathogenic/likely pathogenic KCNJ2 variant; family history; de novo variants; and potentially variant-specific effects on trafficking, PIP2 coupling, channel gating, or Kir2.1–Nav1.5 channelosome behavior.
Clinical cardiac risk: prior syncope, sustained ventricular tachycardia, prolonged Tpeak–Tend, and previous cardiac arrest. A 2023 review also associated micrognathia, periodic paralysis, and amiodarone use with life-threatening events, but treatment association may reflect confounding by severity. (pupaza2023assessmentofsudden pages 9-11)
Sex: evidence is evolving. A 2026 meta-analysis of 259 cardiac cases found more complex ventricular arrhythmias and cardiac arrest among females, whereas males more often had periodic paralysis. Because this synthesis selected cases with cardiac manifestations and pooled case reports, it is hypothesis-generating rather than a population estimate. (garcia2026genderspecificcardiacfeatures pages 1-2, garcia2026genderspecificcardiacfeatures pages 10-11)
Protective factors: no validated protective allele or modifier gene is established. Trigger avoidance, maintenance of an individualized safe potassium range, avoidance of arrhythmogenic/QT-active drugs, and surveillance may reduce attacks or complications but do not prevent inheritance.

3. Phenotypes

Core manifestations

Ventricular electrical instability. Findings include frequent premature ventricular contractions, couplets/bigeminy, polymorphic ventricular ectopy, nonsustained or sustained polymorphic VT, and particularly bidirectional VT. Prominent U waves and prolonged QU are characteristic; QTc can be normal. Estimated ventricular-arrhythmia prevalence is 60–90%, with polymorphic VT reported in 48% and bidirectional VT in 44% in one recent synthesis. In a 15-person KCNJ2 cohort, 75% had ventricular arrhythmia, 6/12 monitored patients had bidirectional VT, 84% had prominent U waves, and 76% had normal QTc. (pupaza2023assessmentofsudden pages 9-11, kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5)
Suggested HPO: Premature ventricular contractions, Bidirectional ventricular tachycardia, Polymorphic ventricular tachycardia, Syncope, Abnormal U wave, Prolonged QT interval, and Sudden cardiac death.
Periodic paralysis/episodic weakness. Attacks are flaccid, episodic, and variable in duration and potassium association; ictal potassium may be low, normal, or high. Between attacks, strength may initially be normal, although fixed/progressive myopathy has been described. In one small cohort, 7/15 had periodic paralysis; attacks occurred in 80% of males versus 20% of females, demonstrating sex-related variability but not a generalizable prevalence estimate. (kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5)
Suggested HPO: Periodic paralysis, Episodic flaccid weakness, Hypokalemia when documented, Muscle weakness, and Myopathy.
Developmental dysmorphism. Common features include hypertelorism, broad forehead, low-set ears, small or receding mandible/micrognathia, dental abnormalities, clinodactyly, syndactyly, short digits or small hands/feet, short stature, and scoliosis. Dysmorphism was recorded in 100% of one intensively phenotyped 15-person cohort but is less consistently recognized in routine practice. (kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5, NCT00521794 chunk 1)
Suggested HPO: Hypertelorism, Micrognathia, Low-set ears, Clinodactyly, Syndactyly, Short stature, and Scoliosis.

Onset, severity, course, and quality of life

Features are often congenital or recognizable in childhood, while episodic weakness and arrhythmia commonly emerge during childhood or adolescence. A 2023 review reported onset before 19 years in 42.3%, but delayed diagnosis into adulthood is common. Severity and expressivity vary markedly within families: some individuals have one component, others the complete triad. Arrhythmia and weakness are generally episodic; developmental abnormalities are stable; fixed myopathy can slowly progress in a minority. (pupaza2023assessmentofsudden pages 9-11)

No validated ATS-specific quality-of-life instrument or robust EQ-5D/SF-36 dataset was found. Nevertheless, recurrent weakness can impair mobility, schooling, work, and exercise; palpitations, syncope, ICD shocks, and fear of sudden death impose substantial psychosocial burden.

4. Genetic and molecular information

Causal gene and variant biology

KCNJ2 is the established causal gene. Pathogenic variants are germline and predominantly heterozygous missense variants, with in-frame deletions and other classes also reported. More than 90 variants were summarized in the 2024 preprint, distributed across Kir2.1; curated clinical classification must be performed variant-by-variant in ClinVar/ClinGen rather than assuming every rare KCNJ2 change is pathogenic. Population frequency should be extremely low or absent in gnomAD for a fully penetrant pathogenic allele, but no universal frequency cutoff substitutes for ACMG/AMP evaluation. (cruz2024kir2.1mutationsdifferentially pages 3-6)

Functional consequences include:

impaired plasma-membrane trafficking;
reduced channel conductance or altered gating;
weakened phosphatidylinositol-4,5-bisphosphate (PIP2) coupling;
dominant-negative suppression because mutant and wild-type subunits coassemble as tetramers;
perturbation of Kir2.1–Nav1.5 macromolecular complexes, reducing both IK1 and, for some variants, sodium current and conduction.

The de novo p.Arg260Pro (R260P) variant caused defective trafficking and a strong dominant-negative reduction of IK1 in heterologous cells. Documented experimental variants also include C122Y, G215D, R67W, S136F, and Δ314–315; these are mechanistically heterogeneous and should not be treated as pharmacologically interchangeable. (barajasmartinez2011biophysicalandmolecular pages 7-8, cruz2024kir2.1mutationsdifferentially pages 20-22)

No reproducible modifier gene, protective variant, anticipation, epigenetic syndrome, recurrent chromosomal rearrangement, or founder effect is established. Germline mosaicism is biologically possible in apparently de novo families but is not quantified. Somatic mutation is not the disease mechanism.

5. Environmental and lifestyle information

Environmental factors modify expression, not occurrence. Patients should identify personal triggers using attack/food/activity records. Abrupt potassium shifts, dehydration, fasting, large carbohydrate loads, cold, vigorous exercise followed by rest, and emotional stress may provoke episodes. Smoking, alcohol, pollution, radiation, occupational toxins, and infectious agents are not established causes. Medication review is important because drugs affecting potassium balance, conduction, or repolarization may worsen either phenotype.

No vaccine or anti-infective strategy is disease-specific. Ordinary immunization remains appropriate unless an individual cardiac or neuromuscular circumstance dictates otherwise.

6. Mechanism and pathophysiology

Causal chain

Upstream: pathogenic KCNJ2 variant → defective Kir2.1 assembly, trafficking, PIP2-dependent gating, or channelosome organization → reduced inward-rectifier potassium current (IK1).

Cardiac downstream: reduced IK1 → less stable ventricular-myocyte resting membrane potential and impaired terminal repolarization → altered sodium-channel availability/conduction and calcium cycling → delayed afterdepolarizations, ectopy, re-entry, polymorphic/bidirectional VT, syncope, and occasionally cardiac arrest. Kir2.1 is particularly important in ventricular cardiomyocytes and Purkinje cells. (pupaza2023assessmentofsudden pages 9-11, cruz2024kir2.1mutationsdifferentially pages 3-6)

Skeletal-muscle downstream: reduced Kir2.1-mediated potassium conductance → unstable myofiber resting potential and paradoxical depolarization/inexcitability during potassium or metabolic shifts → episodic flaccid weakness; repeated or persistent electrical dysfunction may contribute to fixed myopathy.

Developmental downstream: Kir2.1 has non-excitable developmental roles; disturbed membrane bioelectric signaling plausibly contributes to craniofacial and limb patterning. The precise human developmental chain remains less defined than cardiac electrophysiology.

Suggested annotations include GO: inward rectifier potassium channel activity, potassium ion transmembrane transport, regulation of membrane potential, cardiac muscle cell action potential, and cardiac muscle cell repolarization; cellular targets include cardiomyocyte, cardiac Purkinje cell, and skeletal muscle fiber/myocyte.

Molecular profiling and 2024 advance

Chen et al. generated patient hiPSCs carrying KCNJ2 c.199C>T, corrected the variant by CRISPR/HDR, differentiated cardiomyocytes, and performed electrophysiology, RNA-seq, ATAC-seq, WGCNA, and pathway analysis across six developmental time points. Mutant cells beat more slowly, had prolonged action potentials and reduced Kir2.1 current. ZNF528 was persistently downregulated from cardiac mesoderm day 4; seven potassium-related pathways were suppressed (all p<0.05), and KCNJ2, CTTN, and ATP1B1 emerged as consistently downregulated proteins. This provides peer-reviewed, patient-specific multi-omic evidence for developmental regulatory effects beyond the primary channel lesion, but it is a single cellular model and not yet a clinical biomarker. (chen2024transcriptomeandopen pages 1-3, chen2024transcriptomeandopen pages 3-4)

The authors’ abstract conclusion was that the study identified transcription factors and targets related to “electrophysiology and developmental pathogenicity” and potential therapeutic candidates not dependent on gene editing. (chen2024transcriptomeandopen pages 1-3)

No validated ATS metabolomic, lipidomic, immune, inflammatory, or spatial-transcriptomic signature is currently established.

7. Anatomical structures affected

Heart: ventricular myocardium and specialized conduction system/Purkinje network; usually structurally normal. Suggested UBERON: heart, cardiac ventricle, ventricular myocardium, cardiac conduction system.
Skeletal muscle: limb and axial skeletal muscle; clinically bilateral/generalized rather than consistently lateralized. Suggested UBERON: skeletal muscle organ, limb muscle.
Craniofacial skeleton and dentition: mandible/maxilla, ears, facial spacing, teeth.
Limbs/digits and spine: hands, feet, fingers/toes, and vertebral column.
Subcellular: plasma membrane/sarcolemma, Kir2.1 tetrameric channel complex, and associated PIP2/channelosome domains; sarcoplasmic-reticulum effects have also been modeled. Suggested GO cellular-component terms: plasma membrane, sarcolemma, potassium channel complex, and intercalated disc/channelosome where experimentally supported.

8. Temporal development

ATS is congenital genetically and developmentally, but clinical onset is variable. Dysmorphism is present from birth; weakness and arrhythmia commonly become evident in childhood or adolescence. The course is lifelong and fluctuating rather than conventionally staged. Periods without attacks are remission intervals, not cure. Critical opportunities are early recognition after unexplained weakness, characteristic ventricular ectopy, syncope, or identification of an affected relative; early rhythm surveillance and cascade testing may prevent avoidable complications.

9. Inheritance and population

Prevalence is estimated at approximately 1 per 1,000,000; reliable incidence, carrier-frequency, geographic, and ancestry-specific estimates are unavailable. No endemic region or consistently enriched ancestry is established. (garcia2026genderspecificcardiacfeatures pages 1-2, pupaza2023assessmentofsudden pages 9-11)

Inheritance is autosomal dominant with variable expressivity and incomplete penetrance. Each child of a heterozygous affected individual has a 50% probability of inheriting the variant, although phenotype cannot be predicted reliably. De novo cases occur. No anticipation or meaningful role for consanguinity is expected in the usual dominant disorder. Small cohorts suggest periodic paralysis may be more penetrant in males while complex arrhythmia may be more prominent in females, but estimates remain vulnerable to ascertainment bias. (kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5, garcia2026genderspecificcardiacfeatures pages 1-2)

10. Diagnostics

Clinical assessment

A historical practical rule is the presence of at least two of three domains: potassium-sensitive episodic weakness; ventricular electrical abnormalities; and typical dysmorphism. NCT00521794 operationalized this approach and followed 28 participants over two years with standardized strength, cardiac, electrodiagnostic, and optional genetic assessments. (NCT00521794 chunk 1)

Recommended work-up comprises:

Three-generation pedigree and examination for subtle facial/digital features.
Resting 12-lead ECG, emphasizing U waves and QU as well as QTc.
Ambulatory ECG/Holter to quantify PVCs and detect polymorphic/bidirectional VT; exercise testing may reveal or characterize ectopy but requires specialist supervision.
Echocardiography to exclude structural disease and assess ectopy-induced cardiomyopathy.
During weakness: serum potassium, magnesium, glucose, renal function, thyroid testing, creatine kinase, and ECG. Normal interictal potassium does not exclude ATS.
Neuromuscular examination and long-exercise EMG testing where available. Muscle biopsy is not routinely diagnostic; MRI may document chronic myopathy.

Genetic testing

First-line molecular testing is KCNJ2 sequencing with deletion/duplication analysis, or a curated periodic-paralysis/inherited-arrhythmia panel including KCNJ2. A pathogenic/likely pathogenic variant confirms ATS1 in the appropriate phenotype. If negative, re-review phenotype and consider broader panel/WES/WGS for phenocopies or unresolved ATS-like disease. CMA, karyotype, FISH, mitochondrial DNA, and repeat-expansion tests are not routine unless other features indicate them. RNA-seq/ATAC-seq remain research tools, not clinical diagnostics.

Cascade testing should be offered to relatives after identification of a familial pathogenic variant. A VUS must not be used alone for predictive diagnosis or irreversible intervention.

Differential diagnosis

CACNA1S/SCN4A hypokalemic or hyperkalemic periodic paralysis: weakness without the characteristic ATS dysmorphism/ventricular phenotype.
Thyrotoxic periodic paralysis: acquired biochemical hyperthyroidism, often without childhood dysmorphism.
Catecholaminergic polymorphic VT: exercise/emotion-induced bidirectional or polymorphic VT, usually RYR2-related and without periodic paralysis/dysmorphism; ATS can mimic CPVT. (barajasmartinez2011biophysicalandmolecular pages 7-8)
Conventional long-QT syndromes: characteristic QT prolongation and genotype-specific triggers, but not the ATS triad.
Short-QT syndrome type 3: KCNJ2 gain-of-function rather than ATS loss-of-function.
Other causes of ventricular ectopy, U waves, hypokalemia, syncope, neuromuscular weakness, and congenital dysmorphism.

11. Outcome and prognosis

Most patients survive into adulthood, but no robust disease-specific life-expectancy or 5-/10-year overall-survival estimates exist. Morbidity includes recurrent paralysis, fixed weakness/myopathy, syncope, ventricular arrhythmia, treatment adverse effects, device complications, and rare ectopy-induced cardiomyopathy. A 2023 review estimated 5-year cumulative SCD risk at 7.9%. (pupaza2023assessmentofsudden pages 9-11)

One 15-person referral cohort reported syncope/cardiac arrest in 50–60%, but this should not be generalized because of very small sample size and referral enrichment. In the same series, only 25% were clinically asymptomatic. (kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5)

Adverse prognostic markers include previous cardiac arrest, sustained VT, syncope, high/complex ectopic burden, and possible prolonged Tpeak–Tend. Formal prognostic biomarkers, validated risk calculators, and disease-specific patient-reported outcome instruments are lacking.

12. Treatment

Treatment should be coordinated between inherited-arrhythmia cardiology and neuromuscular specialists. No therapy corrects all three disease domains, and no drug is universally effective.

Weakness

During an attack, measure potassium and obtain cardiac monitoring before replacement whenever possible. Oral potassium may help documented hypokalemic attacks but can be hazardous when potassium is normal/high or arrhythmia is active.
Preventive options include individualized potassium management and carbonic-anhydrase inhibitors such as acetazolamide or dichlorphenamide, extrapolated mainly from periodic-paralysis practice. Evidence in ATS is limited, and electrolyte/renal adverse effects require monitoring.
Physical and occupational therapy, fall prevention, mobility aids, and graded activity support function; strenuous trigger activity followed by abrupt rest may need modification.

Suggested NCIT interventions: Potassium Supplementation, Acetazolamide, Physical Therapy, and Occupational Therapy.

Arrhythmia

Beta-blockers are frequently used, especially for symptomatic or adrenergically influenced arrhythmia, but response is variable and excessive bradycardia may worsen ectopy. In one cohort, all arrhythmic patients received beta-blockers, most often bisoprolol. (kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5)
Flecainide has reduced PVC/VT burden in multiple reports and may be combined with a beta-blocker. The R260P case remained symptomatic on nadolol but responded to flecainide. (barajasmartinez2011biophysicalandmolecular pages 7-8)
Treatment must now be viewed as potentially variant-specific. A December 2024 preprint review of 53 treated ATS1 patients reported partial response in 54%, ventricular-arrhythmia reduction in only 23%, ineffectiveness in 23%, and nonfatal cardiac arrest in 13.5%. Mouse and patient-specific iPSC-CM models showed that flecainide could reduce conduction velocity and increase inducible arrhythmia/rotors for several variants, whereas S136F behaved more favorably. The authors concluded: “Class-Ic AADs are only partially effective and might be proarrhythmic in some ATS1 patients.” These provocative findings require peer-reviewed replication and should prompt close ECG/Holter monitoring rather than abrupt unsupervised discontinuation. (cruz2024kir2.1mutationsdifferentially pages 20-22, cruz2024kir2.1mutationsdifferentially pages 3-6)
An ICD is appropriate for survivors of cardiac arrest and selected patients with recurrent hemodynamically significant sustained VT despite therapy. Frequent but tolerated ectopy alone does not automatically justify implantation. In one enriched cohort, 40% received ICDs. (kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5)
Catheter ablation can be considered for a dominant, mappable PVC/VT focus or ectopy-induced cardiomyopathy, but multifocal disease limits efficacy.
Amiodarone is not a preferred routine ATS therapy; observational association with adverse events may reflect both pharmacology and confounding by indication.

Suggested NCIT terms: Beta-Adrenergic Receptor Blocker Therapy, Flecainide, Implantable Cardioverter-Defibrillator, and Catheter Ablation.

Trials and advanced therapy

NCT00521794: completed observational natural-history study, 28 participants.
NCT00839501: phase 1 potassium/acetazolamide study, terminated after 3 participants.
NCT06205550: phase 2 N-of-1 study in ATS and MEPPC, planned enrollment 10 and listed as not yet recruiting in the retrieved record.
No approved ATS gene, RNA, cell, or CRISPR therapy exists. Gene addition is conceptually complicated by dominant-negative alleles and the need to target both cardiac and skeletal muscle safely. The 2024 CRISPR-corrected iPSC model is a mechanistic platform, not a clinical intervention. (chen2024transcriptomeandopen pages 1-3, chen2024transcriptomeandopen pages 3-4)

13. Prevention

Primary prevention of the genotype is not possible after conception. Reproductive options include preconception counseling, prenatal diagnosis, and preimplantation genetic testing when a familial pathogenic variant is known.

Secondary prevention includes cascade genetic testing, ECG/Holter assessment of carriers, and evaluation of asymptomatic children because disease can begin early. ATS is not part of standard biochemical newborn screening; genomic newborn screening remains investigational.

Tertiary prevention includes individualized trigger avoidance, electrolyte management, medication-interaction review, rhythm surveillance, emergency plans for prolonged paralysis/syncope, and ICD therapy in appropriately selected high-risk patients. Family members should understand autosomal-dominant recurrence risk and the inability to predict severity from inheritance alone.

14. Other species and natural disease

Kir2.1/KCNJ2 function is evolutionarily conserved across vertebrates. However, no well-established, naturally occurring companion-animal ATS with a validated breed association was identified in the retrieved evidence. Consequently, no VBO breed term, zoonotic potential, transmission pathway, or veterinary public-health concern applies. ATS is inherited, not contagious.

15. Model organisms and experimental systems

Heterologous cells: HEK-cell expression permits trafficking, current-density, and dominant-negative testing. R260P markedly reduced IK1 and membrane trafficking. Strength: clean variant biophysics; limitation: lacks mature cardiac architecture. (barajasmartinez2011biophysicalandmolecular pages 7-8)
Mouse models: cardiac AAV/transduction models expressing C122Y, G215D, Δ314–315, R67W, or S136F reproduce variant-dependent ECG and arrhythmia phenotypes. Flecainide increased inducibility in most tested mutants but reduced arrhythmia in S136F, supporting pharmacogenetic heterogeneity. Limitation: cardiac-restricted, acute expression and murine electrophysiology do not reproduce the full human developmental/neuromuscular syndrome. (cruz2024kir2.1mutationsdifferentially pages 20-22, cruz2024kir2.1mutationsdifferentially pages 3-6)
Patient-specific hiPSC cardiomyocytes: reproduce reduced IK1, prolonged action potential, slow beating, conduction abnormalities, and re-entry; CRISPR-isogenic repair strengthens causal inference. Limitations include fetal-like electrophysiology and absence of whole-organ autonomic and mechanical context. (chen2024transcriptomeandopen pages 1-3, chen2024transcriptomeandopen pages 3-4)
In-silico structural/docking models: predict mutation-specific changes around the Kir2.1 Cys311 flecainide pharmacophore. These generate hypotheses and cannot independently establish clinical drug response. (cruz2024kir2.1mutationsdifferentially pages 20-22)
Needed next models: skeletal-muscle iPSC/myotube systems, dual cardiac–skeletal organoids, mature engineered tissues, and knock-in animals carrying patient variants under endogenous regulation.

Evidence-quality conclusions and knowledge gaps

The causal KCNJ2–Kir2.1–IK1 relationship is supported by convergent human genetic, heterologous-cell, animal, and isogenic iPSC evidence. Clinical frequencies and treatment effects are less certain because ATS is rare, expressivity is broad, and published cohorts are referral-enriched. The most important 2024 advances were (1) developmental RNA/ATAC profiling that implicated ZNF528, CTTN, and ATP1B1 and (2) mutation-specific experimental evidence questioning uniform flecainide safety. The latter remains preprint-level evidence and should be treated as a signal for prospective, genotype-stratified trials—not as definitive proof that flecainide is broadly harmful. (cruz2024kir2.1mutationsdifferentially pages 20-22, chen2024transcriptomeandopen pages 1-3)

Priority research needs are an international prospective registry; standardized phenotype, quality-of-life, and attack outcomes; ClinGen-level variant curation; variant-stratified antiarrhythmic studies; validated SCD-risk prediction; skeletal-muscle models; and therapeutic approaches capable of addressing dominant-negative disease in both heart and skeletal muscle.

References

(pupaza2023assessmentofsudden pages 9-11): Adelina Pupaza, Eliza Cinteza, Corina Maria Vasile, Alin Nicolescu, and Radu Vatasescu. Assessment of sudden cardiac death risk in pediatric primary electrical disorders: a comprehensive overview. Diagnostics, 13:3551, Nov 2023. URL: https://doi.org/10.3390/diagnostics13233551, doi:10.3390/diagnostics13233551. This article has 7 citations.
(OpenTargets Search: Andersen-Tawil syndrome-KCNJ2): Open Targets Query (Andersen-Tawil syndrome-KCNJ2, 2 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
(barajasmartinez2011biophysicalandmolecular pages 7-8): Hector Barajas-Martinez, Dan Hu, Gustavo Ontiveros, Gabriel Caceres, Mayurika Desai, Elena Burashnikov, Jorge Scaglione, and Charles Antzelevitch. Biophysical and molecular characterization of a novel de novo kcnj2 mutation associated with andersen-tawil syndrome and catecholaminergic polymorphic ventricular tachycardia mimicry. Circulation: Cardiovascular Genetics, 4:51–57, Feb 2011. URL: https://doi.org/10.1161/circgenetics.110.957696, doi:10.1161/circgenetics.110.957696. This article has 50 citations.
(cruz2024kir2.1mutationsdifferentially pages 3-6): Francisco M. Cruz, Ana I. Moreno-Manuel, Sánchez Pérez Patricia, Juan Manuel Ruiz-Robles, Paula García Socuellamos, Lilian K. Gutiérrez, María Linarejos Vera-Pedrosa, Amaia Talavera Gutierrez, Gema Mondéjar Parreño, Álvaro Macías, Isabel Martínez-Carrascoso, Francisco J Bermúdez-Jiménez, Salvador Arias Santiago, Fernando Martínez de Benito, Aitana Braza-Boils, Carmen Valenzuela, CA Morillo, Esther Zorio, Juan Jiménez-Jaimez, and José Jalife. Kir2.1 mutations differentially increase the risk of flecainide proarrhythmia in andersen tawil syndrome. MedRxiv, Dec 2024. URL: https://doi.org/10.1101/2024.12.10.24318629, doi:10.1101/2024.12.10.24318629. This article has 1 citations.
(kostera‐pruszczyk2015andersen–tawilsyndromereport pages 4-5): Anna Kostera‐Pruszczyk, Anna Potulska‐Chromik, Piotr Pruszczyk, Katarzyna Bieganowska, Maria Miszczak‐Knecht, Piotr Bienias, krzysztof szczałuba, Hsien‐Yang Lee, Emily Quinn, Rafal Ploski, Anna Kaminska, and Louis J. Ptáček. Andersen–tawil syndrome: report of 3 novel mutations and high risk of symptomatic cardiac involvement. Muscle & Nerve, 51:192-196, Feb 2015. URL: https://doi.org/10.1002/mus.24293, doi:10.1002/mus.24293. This article has 28 citations and is from a peer-reviewed journal.
(garcia2026genderspecificcardiacfeatures pages 1-2): Alan Garcia, Abdul Mueez Alam Kayani, Ricky Lemus-Zamora, Daniel Alejandro Navarro-Martinez, Eduardo Tellez-Garcia, Richard Salama-Frisbie, Jorge Gomez Flores, Eduardo Aviles, and Brijesh Patel. Gender-specific cardiac features in andersen–tawil syndrome: a comprehensive meta-analysis of case reports and series. Journal of Interventional Cardiac Electrophysiology, Jan 2026. URL: https://doi.org/10.1007/s10840-026-02237-6, doi:10.1007/s10840-026-02237-6. This article has 1 citations and is from a peer-reviewed journal.
(NCT00521794 chunk 1): Robert Griggs, MD. Characteristics of Andersen-Tawil Syndrome. University of Rochester. 2007. ClinicalTrials.gov Identifier: NCT00521794
(cruz2024kir2.1mutationsdifferentially pages 22-24): Francisco M. Cruz, Ana I. Moreno-Manuel, Sánchez Pérez Patricia, Juan Manuel Ruiz-Robles, Paula García Socuellamos, Lilian K. Gutiérrez, María Linarejos Vera-Pedrosa, Amaia Talavera Gutierrez, Gema Mondéjar Parreño, Álvaro Macías, Isabel Martínez-Carrascoso, Francisco J Bermúdez-Jiménez, Salvador Arias Santiago, Fernando Martínez de Benito, Aitana Braza-Boils, Carmen Valenzuela, CA Morillo, Esther Zorio, Juan Jiménez-Jaimez, and José Jalife. Kir2.1 mutations differentially increase the risk of flecainide proarrhythmia in andersen tawil syndrome. MedRxiv, Dec 2024. URL: https://doi.org/10.1101/2024.12.10.24318629, doi:10.1101/2024.12.10.24318629. This article has 1 citations.
(cruz2024kir2.1mutationsdifferentially pages 20-22): Francisco M. Cruz, Ana I. Moreno-Manuel, Sánchez Pérez Patricia, Juan Manuel Ruiz-Robles, Paula García Socuellamos, Lilian K. Gutiérrez, María Linarejos Vera-Pedrosa, Amaia Talavera Gutierrez, Gema Mondéjar Parreño, Álvaro Macías, Isabel Martínez-Carrascoso, Francisco J Bermúdez-Jiménez, Salvador Arias Santiago, Fernando Martínez de Benito, Aitana Braza-Boils, Carmen Valenzuela, CA Morillo, Esther Zorio, Juan Jiménez-Jaimez, and José Jalife. Kir2.1 mutations differentially increase the risk of flecainide proarrhythmia in andersen tawil syndrome. MedRxiv, Dec 2024. URL: https://doi.org/10.1101/2024.12.10.24318629, doi:10.1101/2024.12.10.24318629. This article has 1 citations.
(chen2024transcriptomeandopen pages 1-3): Peipei Chen, Junyu Long, Tianrui Hua, Zhifa Zheng, Ying Xiao, Lianfeng Chen, Kang Yu, Wei Wu, and Shuyang Zhang. Transcriptome and open chromatin analysis reveals the process of myocardial cell development and key pathogenic target proteins in long qt syndrome type 7. Journal of Translational Medicine, Mar 2024. URL: https://doi.org/10.1186/s12967-024-05125-7, doi:10.1186/s12967-024-05125-7. This article has 1 citations and is from a peer-reviewed journal.
(chen2024transcriptomeandopen pages 3-4): Peipei Chen, Junyu Long, Tianrui Hua, Zhifa Zheng, Ying Xiao, Lianfeng Chen, Kang Yu, Wei Wu, and Shuyang Zhang. Transcriptome and open chromatin analysis reveals the process of myocardial cell development and key pathogenic target proteins in long qt syndrome type 7. Journal of Translational Medicine, Mar 2024. URL: https://doi.org/10.1186/s12967-024-05125-7, doi:10.1186/s12967-024-05125-7. This article has 1 citations and is from a peer-reviewed journal.
(garcia2026genderspecificcardiacfeatures pages 10-11): Alan Garcia, Abdul Mueez Alam Kayani, Ricky Lemus-Zamora, Daniel Alejandro Navarro-Martinez, Eduardo Tellez-Garcia, Richard Salama-Frisbie, Jorge Gomez Flores, Eduardo Aviles, and Brijesh Patel. Gender-specific cardiac features in andersen–tawil syndrome: a comprehensive meta-analysis of case reports and series. Journal of Interventional Cardiac Electrophysiology, Jan 2026. URL: https://doi.org/10.1007/s10840-026-02237-6, doi:10.1007/s10840-026-02237-6. This article has 1 citations and is from a peer-reviewed journal.

Artifacts

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OpenScientist Report

Classifications

Mappings

Inheritance

Mechanistic Hypotheses

Discussions and Knowledge Gaps

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Differential Diagnoses

Clinical Trials

Source YAML

References & Deep Research

References

Deep Research

Disease Characteristics Research Template

Target Disease

Research Objectives

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome/Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Citation Requirements

Output Format

Andersen–Tawil syndrome: disease-characteristics research report

Executive summary

1. Disease information

Definition and identifiers

2. Etiology, risk, protection, and gene–environment interaction

Causal factors

Risk and protective factors

3. Phenotypes

Core manifestations

Onset, severity, course, and quality of life

4. Genetic and molecular information

Causal gene and variant biology

5. Environmental and lifestyle information

6. Mechanism and pathophysiology

Causal chain

Molecular profiling and 2024 advance

7. Anatomical structures affected

8. Temporal development

9. Inheritance and population

10. Diagnostics

Clinical assessment

Genetic testing

Differential diagnosis

11. Outcome and prognosis

12. Treatment

Weakness

Arrhythmia

Trials and advanced therapy

13. Prevention

14. Other species and natural disease

15. Model organisms and experimental systems

Evidence-quality conclusions and knowledge gaps

Artifacts