Channelopathies
Definition
Channelopathies are the inherited primary electrical diseases of the heart: arrhythmia syndromes in which the substrate is abnormal ion-channel function rather than structural myocardium. The organising principle is direction of effect — gain-of-function variants increase a current, loss-of-function variants reduce it — and direction, not gene identity, determines the phenotype. SCN5A is the clearest case: gain-of-function prolongs the plateau and produces LQT3, loss-of-function slows conduction and produces Brugada syndrome. Six syndromes are conventionally grouped under the term — long QT, short QT, Brugada, early repolarisation, catecholaminergic polymorphic VT and idiopathic VF — and the review underlying this page states that together they account for more than half of sudden cardiac death in people under 50. (sources/channelopathies-jaha-2025, rating: high)
Key Concepts
The Six Syndromes
| Syndrome |
Defining feature |
Principal genes |
| Long-QT-Syndrome |
QTc prolongation; torsades de pointes |
KCNQ1, KCNH2, SCN5A, CALM1/2/3, CACNA1C |
| Short-QT-Syndrome |
QTc <340 ms; short-coupled VF |
KCNH2, KCNQ1, KCNJ2, CACNA1C/CACNB2/CACNA2D1 |
| Brugada-Syndrome |
Type 1 coved pattern in V1–V2; VF |
SCN5A, plus >27 other genes |
| Early-Repolarization-Syndrome |
J-point elevation in inferior or lateral leads; VF |
KCNJ8, ABCC9, KCND3 |
| CPVT |
Exercise- or emotion-induced bidirectional VT |
RYR2, CASQ2 |
| Idiopathic-Ventricular-Fibrillation |
VF after exclusion of all other causes |
CALM1, RYR2, IRX family, DPP6 |
- The boundaries between syndromes are porous. Brugada and early repolarisation phenotypes overlap, as do long and short QT, and CPVT shares triggers and genes with idiopathic VF. Classification follows the dominant ECG pattern and clinical trigger rather than the gene. (sources/channelopathies-jaha-2025)
Gain- versus Loss-of-Function
| Current |
Direction |
Cellular effect |
Syndrome |
| INa (SCN5A) |
Gain |
Persistent inward Na⁺ prolongs the plateau |
LQT3 |
| INa (SCN5A) |
Loss |
Reduced INa slows conduction, particularly in the RV outflow tract |
Brugada |
| IKs (KCNQ1), IKr (KCNH2) |
Loss |
Impaired repolarisation prolongs the action potential |
LQT1, LQT2 |
| IKs, IKr, IK1 |
Gain |
Accelerated repolarisation shortens the action potential |
Short QT |
| Ito, IK-ATP (KCNJ8, ABCC9, KCND3) |
Gain |
Epicardial outward shift creates repolarisation heterogeneity |
Brugada, ERS |
| ICa,L (CACNA1C, CACNB2, CACNA2D1) |
Loss |
Shortened plateau |
Brugada, short QT, ERS |
| RYR2 |
Gain |
Diastolic sarcoplasmic Ca²⁺ leak → delayed afterdepolarisations |
CPVT |
- Direction determines therapy, not gene. A sodium-channel blocker is rational in LQT3 gain-of-function and harmful in Brugada loss-of-function, so the same drug can be correct in one patient and proarrhythmic in another with a variant in the same gene. (sources/channelopathies-jaha-2025)
Epidemiology
| Syndrome |
Prevalence |
Notes |
| LQTS |
~1:2500; possibly 1:2000 allowing for silent carriers |
Most common channelopathy; pathogenic-genotype prevalence estimated at 1:80 from Exome Sequencing Project data |
| Brugada |
3–5 per 10,000 |
8–10× more common in men; about two-thirds asymptomatic; 4–12% of all SCD and up to 28% of SCD with structurally normal hearts |
| CPVT |
~1 per 10,000 |
~15% of SCD in the young; up to 50% mortality by age 35 if unrecognised |
| Short QT |
0.02–0.1% of adults |
Male predominance; autosomal dominant with low penetrance |
| ERS |
~5.8% of adults; up to 33.9% of athletes |
More common in Black and Southeast Asian individuals |
- Risk is age- and sex-dependent. In LQTS, males aged 10–12 carry a fourfold higher relative risk, risk equalises in mid-adolescence, and women aged 18–40 carry higher absolute risk (11% vs 2%) because oestrogen inhibits IKr; testosterone shortens the QT interval in postpubertal males, and the postpartum period is the highest-risk phase for women. See concepts/Sex-Differences-in-Channelopathies. (sources/channelopathies-jaha-2025)
- The young are a different epidemiological population. Sudden death in 1–35-year-olds occurs at 1.3–3.2 per 100,000 person-years, and 40% of autopsies show a structurally normal heart — the channelopathy share. Coronary disease accounts for 24% and inherited cardiomyopathy for 16% at this age, inverting the adult pattern, where coronary disease causes ~80% and the mean age is 65. (sources/inherited-arrhythmias-nrdp-2020, rating: very high)
- Prevalence varies by ancestry in Brugada syndrome: 0.0–0.94% in Asians, 0.15% in Japanese-Americans, 0.0–0.02% in Europeans and 0.005–0.1% in North Americans. LQTS has well-described founder mutations in Finland, South Africa, Canada, the Netherlands and Sweden, so regional prevalence is higher than the global figure. (sources/inherited-arrhythmias-nrdp-2020)
Genetic Architecture
- Brugada syndrome is polygenic, not monogenic. More than 250 pathogenic variants across more than 27 genes are described, but SCN5A explains only 15–28% of cases — too little to support a single-gene model. (sources/channelopathies-jaha-2025)
- LQTS has 17 numbered subtypes, but few survive curation. ClinGen now classifies KCNQ1 (LQT1), KCNH2 (LQT2), CALM1/2/3 and CACNA1C as definitive, with SCN5A handled under a broad "SCN5A-related cardiac rhythm disorder" designation; SCN4B is disputed, CAV3 and KCNJ2 have limited evidence for isolated LQTS, and KCNE2 (LQT6) does not appear among the current definitive curations. Reporting variants in the remainder as pathogenic misclassifies patients. (sources/clingen-summary-2026-05-09, rating: high)
- Subtype frequencies depend on ascertainment. LQT1 accounts for 30–50% and LQT2 for 25–40% depending on whether the cohort was prospectively screened or registry-based; LQT3 is consistently 5–10%. Older symptomatic registries report 30–35% and 25–30% respectively. (sources/lqts-nejm-2025, rating: very high; sources/lqts-jaccep-2022, rating: high)
- LQTS is the one channelopathy with a measured birth prevalence: 17 cases among 43,080 white infants in a prospective 44,596-infant ECG study — 1 in 2,534 (95% CI 1 in 1,583 to 1 in 4,350), with a working estimate of ≥1 in 2,000 once QTc 450–470 ms infants are counted. Variants were found in 29% of infants with QTc 451–460 ms and 49% of those >470 ms. (sources/inherited-arrhythmias-nrdp-2020, rating: very high)
- Inheritance is mostly autosomal dominant, with two exceptions that matter clinically: CPVT2 (CASQ2) and Jervell and Lange-Nielsen syndrome (biallelic KCNQ1 or KCNE1) are recessive, and calmodulinopathy is often de novo, so a negative family history does not exclude it. (sources/channelopathies-jaha-2025)
- A fifth to a sixth of clinically definite LQTS has no identified variant, and 5–10% carry multiple mutations — the latter presenting younger and more severely. This is a reminder that a negative panel does not exclude disease and a positive panel may return more than one finding. (sources/inherited-arrhythmias-nrdp-2020)
Beyond Ion Channels
- ANK2 (LQT4) is a scaffold protein; loss-of-function causes abnormal ion-channel localisation rather than direct pore dysfunction. (sources/channelopathies-jaha-2025)
- PKP2 is desmosomal, yet loss-of-function reduces INa and is associated with both Brugada syndrome and CPVT — a structural protein with electrophysiological consequences. (sources/channelopathies-jaha-2025)
- CAV3 (LQT9) and SNTA1 (LQT12) are loss-of-function variants that increase INa, so they behave directionally like LQT3 despite not being pore subunits. (sources/channelopathies-jaha-2025)
- Variants can act at any level — gating, conformation, trafficking, drug binding or interaction with intracellular regulators — which is why two variants in one gene can respond differently to the same drug. (sources/channelopathies-jaha-2025)
Diagnosis
| Syndrome |
Score |
Low |
Intermediate |
Probable or definite |
| LQTS |
Schwartz |
≤1 |
>1–3 |
≥3.5 |
| Short QT |
Schwartz SQTS |
≤2 |
3 |
≥4 |
| Brugada |
Shanghai |
<2 |
2–3 |
≥3.5 |
| ERS |
Shanghai ERS |
<3 |
3–4.5 |
≥5 |
(sources/channelopathies-jaha-2025; see concepts/Shanghai-Score-System for the BrS and ERS criteria in full)
- Provocation unmasks concealed phenotypes. Ajmaline, flecainide or procainamide for Brugada; exercise testing for CPVT, where bidirectional or polymorphic VT at high workload is characteristic and a negative test does not exclude the diagnosis (sensitivity ~67%); epinephrine infusion when exercise is not feasible. (sources/channelopathies-jaha-2025)
- Genetic testing is indicated in clinically suspected CPVT, high-suspicion LQTS with a negative workup, unexplained cardiac arrest, and family members of an affected proband. Indications, panel composition and yields by syndrome: concepts/Genetic-Testing-in-Arrhythmias. (sources/channelopathies-jaha-2025)
- VUS results dominate clinical testing and provide neither reassurance nor a management pathway; high-throughput automated patch-clamp assays are being developed to classify them functionally. See concepts/ClinGen-Gene-Disease-Validity. (sources/channelopathies-jaha-2025)
- Measurement method is part of the diagnosis. The tangent method for QTc can underestimate the interval when the T-wave descent has a slow component — common in IKs/IKr impairment — and should not be used when LQTS is suspected. (sources/inherited-arrhythmias-nrdp-2020, rating: very high)
- A short QT interval is not a diagnosis on its own. QTc <340 ms occurs in 0.4% of a Finnish population cohort and <320 ms in 0.1% (0.05% of children), and short QT alone was not associated with arrhythmic events; the SQTS threshold therefore overlaps the healthy range. (sources/inherited-arrhythmias-nrdp-2020)
- A rare RYR2 missense variant sits in 3% of healthy people, so a compelling CPVT phenotype gives only ~20:1 odds that the variant is causal — the reason the clinical stress test, not the panel, remains the diagnostic test. (sources/inherited-arrhythmias-nrdp-2020)
Management Principles
| Syndrome |
Core therapy |
Caveat |
| LQTS |
Non-selective beta-blocker, nadolol preferred; LCSD if insufficient; mexiletine in LQT3; ICD for secondary prevention and high-risk primary prevention |
Persistent QTc >500 ms after LCSD is an ICD indication |
| Brugada |
Trigger avoidance; ICD if symptomatic or high-risk; quinidine where ICD is declined or unsuitable; isoproterenol for electrical storm; epicardial RV ablation for recurrent shocks |
Fever and sodium-channel blockers unmask the pattern |
| CPVT |
Non-selective beta-blocker for all, plus exercise restriction; flecainide add-on (~30% need it); LCSD if refractory |
ICD is last resort — shocks provoke catecholamine surges |
| Short QT |
ICD for symptomatic patients; quinidine first-line drug |
Amiodarone and sotalol are ineffective in SQTS1 |
| ERS |
None if asymptomatic; ICD after cardiac arrest; quinidine, isoproterenol or cilostazol/milrinone for storm |
— |
| Idiopathic VF |
Isoproterenol, verapamil or quinidine acutely; ICD; ablation of short-coupled PVC triggers |
Purely exclusionary diagnosis |
(sources/channelopathies-jaha-2025)
- Management is genotype-directed at the margins. Mexiletine in LQT3, avoidance of sodium-channel blockade in Brugada, and quinidine in short QT and ERS all follow from the direction of the underlying current, not from the syndrome label alone. See concepts/Precision-Medicine-LQTS. (sources/channelopathies-jaha-2025)
- Only propranolol and nadolol are established beta-blockers for LQTS; metoprolol should not be used, atenolol is doubtful and the rest are unproven. Exceptions to treating every diagnosed patient are asymptomatic males with LQT1 still event-free off therapy at 25 and genotype-positive phenotype-negative individuals. (sources/inherited-arrhythmias-nrdp-2020, rating: very high)
- LCSD must section the lower half of the left stellate ganglion and the first four thoracic ganglia. The commonest cause of breakthrough events after surgery is a procedure that removed only the stellate ganglion, so the operation is not interchangeable between centres. See concepts/Left-Cardiac-Sympathetic-Denervation. (sources/inherited-arrhythmias-nrdp-2020)
- In CPVT, the device can kill. Inappropriate shocks from sinus tachycardia or AF trigger an adrenergic storm; contemporary centres reserve ICDs for arrest requiring external defibrillation and favour triple therapy with nadolol, flecainide and LCSD. (sources/inherited-arrhythmias-nrdp-2020)
- Emerging therapies are variant-specific: lumacaftor to rescue KCNH2 trafficking in LQT2, iPSC-derived cardiomyocytes for drug screening, and allele-specific CRISPR approaches, including CASQ2 reconstitution and suppression of mutant RYR2 in CPVT models. See concepts/CRISPR-Cas9-in-Channelopathies. (sources/channelopathies-jaha-2025)
Contradictions / Open Questions
- One gene, opposite phenotypes. Gain-of-function SCN5A causes LQT3; loss-of-function causes Brugada syndrome. Establishing the direction of effect for each variant is a precondition for treatment, because a sodium-channel blocker that helps LQT3 will worsen Brugada — yet most variants are classified without functional data. (sources/channelopathies-jaha-2025, rating: high)
- "Seventeen LQTS subtypes" conflicts with gene curation. The numbered subtype system predates ClinGen review, which leaves only KCNQ1, KCNH2, CALM1/2/3 and CACNA1C definitive and disputes or removes several numbered genes. Both statements are current in the literature, and the label a patient receives depends on which convention their laboratory follows. (sources/channelopathies-jaha-2025; sources/clingen-summary-2026-05-09)
- Subtype frequencies differ by ascertainment, not biology. LQT1 is quoted as 30–35% in older registries and up to 50% in prospective screening; LQT2 as 25–30% or up to 40%. Prospective screening captures a milder, broader spectrum, so the higher numbers are not evidence that the underlying distribution changed. (sources/channelopathies-jaha-2025; sources/lqts-nejm-2025; sources/lqts-jaccep-2022)
- VUS prevalence limits clinical utility. Most individuals undergoing channelopathy genetic testing receive a variant of uncertain significance in a gene such as KCNQ1 or KCNH2, which neither confirms nor excludes the diagnosis. Until functional classification is routine, a "positive" panel result has an uncertain yield. (sources/channelopathies-jaha-2025)
- The Brugada mechanism is unresolved. The repolarisation hypothesis (outward current shift in RV epicardium, phase 2 re-entry) and the depolarisation hypothesis (reduced sodium current and connexin 43, slow conduction in the RV outflow tract) coexist and are not mutually exclusive; their relative contribution may vary by patient and variant. (sources/channelopathies-jaha-2025)
- The quinidine paradox. Amiodarone and sotalol block IKr and prolong QT in normal hearts, yet are ineffective in SQTS1, where a KCNH2 gain-of-function shortens it. The most economical explanation is that the mutation alters drug-binding conformation or gating so that class-level predictions fail — an argument for variant-level drug testing. (sources/channelopathies-jaha-2025)
- ICD therapy is proarrhythmic in CPVT. Shocks trigger catecholaminergic surges that can provoke further arrhythmia; devices convert VF but generally fail to terminate VT. Guidelines have moved to ICD-as-last-resort without randomised evidence. (sources/channelopathies-jaha-2025)
- Idiopathic VF is defined by exclusion. There is no pathognomonic finding, the category subsumes heterogeneous causes, and as genetic and functional knowledge expands many diagnoses are likely to be reclassified into more specific entities. (sources/channelopathies-jaha-2025)
- The unifying mechanism is inferred from canine wedge experiments. Spatial dispersion of repolarisation is presented as the common pathway for all four syndromes, but the evidence base is largely wedge preparations and the interpretations are not uniform among electrophysiologists. A hypothesis that explains everything is difficult to falsify. (sources/inherited-arrhythmias-nrdp-2020, rating: very high)
- Andersen–Tawil may not belong in LQTS at all. The apparent QT prolongation may be an artefact of including a prominent U wave in the QTc calculation, and the Primer argues the syndrome should be separated from the LQTS spectrum — a classification the older subtype numbering (LQT7) still encodes. (sources/inherited-arrhythmias-nrdp-2020)
- Two mechanistic accounts of CPVT coexist: epicardial ectopy generating dispersion and reentry (wedge experiments; suppressed by propranolol and verapamil) versus His–Purkinje DAD-triggered focal activity (transgenic mice). The Primer leaves both standing. (sources/inherited-arrhythmias-nrdp-2020)
- Gene curation is not stable across sources. The 2020 Primer classes KCNE1 as limited evidence for LQTS, yet biallelic KCNE1 is an established cause of Jervell and Lange-Nielsen syndrome — a designation that would be impossible under a strict isolated-LQTS reading. ClinGen curations are phenotype-specific, and a "disputed" label for one phenotype can coexist with definitive evidence for another. (sources/inherited-arrhythmias-nrdp-2020; sources/clingen-summary-2026-05-09)
- Sudden infant death is not all infanticide. About 10% of infants dying suddenly in the first year carry LQTS-causing variants, which supports neonatal ECG screening and argues for restraint before recurrent infant deaths are attributed to homicide. (sources/inherited-arrhythmias-nrdp-2020)
Connections
Sources