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PubMed This is a summary of 17 peer-reviewed journal articles Updated
Cardiology · Long QT Syndrome

The Genetics and Subtypes of LQTS

At a Glance

Long QT Syndrome (LQTS) is a genetic disorder primarily caused by mutations in three genes: KCNQ1, KCNH2, and SCN5A. Because gene carriers can have normal ECGs or vary widely in their symptoms, genetic testing is the most reliable way to identify family members at risk.

LQTS is not a single disease, but a group of related genetic conditions. Your genetic “blueprint” (DNA) contains instructions for building the tiny ion channels that control your heart’s electrical reset [1]. When there is a “typo” (mutation) in these instructions, the heart’s timing is affected [2].

The “Big Three” Genes

While many genes can be involved, about 90% of people with a known genetic cause for LQTS have a mutation in one of three primary genes [3][4].

  • LQT1 (Gene: KCNQ1): This is the most common form. It affects the “slow” potassium channels [5]. Because these channels are crucial during exercise, people with LQT1 are most vulnerable during physical activity, particularly swimming [6].
  • LQT2 (Gene: KCNH2): This affects the “fast” potassium channels [5]. It is often triggered by sudden noises or emotional stress [6].
  • LQT3 (Gene: SCN5A): Unlike the others, this involves sodium channels. It is a “gain-of-function” mutation, meaning the channel stays open too long, like a leaky faucet [2][7]. This type is most dangerous during sleep or rest when the heart rate is slow [6].

Romano-Ward vs. Jervell and Lange-Nielsen

Geneticists categorize LQTS based on how it is inherited and which symptoms appear alongside the heart issues.

  1. Romano-Ward Syndrome (RWS): This is the “standard” form of LQTS. It is inherited in an autosomal dominant pattern, meaning you only need to inherit one copy of the mutated gene from one parent to have the condition [8][9]. It affects the heart but does not affect hearing [8].
  2. Jervell and Lange-Nielsen Syndrome (JLNS): This is a much rarer and more severe form. it is inherited in an autosomal recessive pattern, meaning a child must inherit two copies of the mutated gene (one from each parent) [10][8]. JLNS is characterized by very long QT intervals and congenital deafness (hearing loss present from birth) [10][11].

Why “Normal” Isn’t Always Normal

One of the most confusing parts of LQTS genetics is that the gene doesn’t always “show up” the same way in every person.

  • Incomplete Penetrance: This is the reason why some people carry the LQTS gene but have a perfectly normal-looking ECG at rest [12][13]. These individuals are sometimes called “silent” or “concealed” carriers [13]. Even though their ECG is normal, they can still pass the gene to their children and may still be at risk during high-stress situations or when taking certain medications [13][14].
  • Variable Expressivity: This describes how members of the same family, with the exact same mutation, can have very different experiences [15]. One person might have frequent fainting spells, while their sibling (with the same gene) may never have a single symptom [16][17]. This variability is driven by other “modifier” genes, hormones, and environmental triggers [17][16].

Because of these factors, genetic testing is often the most reliable way to identify family members at risk, even if their heart tests look normal today [14][13].

Common questions in this guide

What are the most common genes that cause Long QT Syndrome?
About 90% of people with a known genetic cause for LQTS have a mutation in one of three primary genes. These are KCNQ1 which causes LQT1, KCNH2 which causes LQT2, and SCN5A which causes LQT3.
Can I carry the LQTS gene even if my ECG is normal?
Yes, this is known as incomplete penetrance. Some people have the LQTS gene mutation but their resting ECG appears completely normal, which is why genetic testing is often recommended for family members.
What is the difference between Romano-Ward and Jervell and Lange-Nielsen syndromes?
Romano-Ward is the most common form of LQTS that only affects the heart and is inherited from one parent. Jervell and Lange-Nielsen is a severe form inherited from both parents that causes heart issues and congenital hearing loss present from birth.
Why do my family members have different LQTS symptoms if we have the same mutation?
This happens because of variable expressivity. Even with the exact same genetic mutation, different family members can have very different symptoms based on other modifying genes, hormones, and environmental triggers.
Do LQT1, LQT2, and LQT3 have different triggers?
Yes, each type has different risk periods. LQT1 is typically triggered by physical activity like swimming, and LQT2 is often triggered by sudden noises or emotional stress. LQT3 is most dangerous during sleep or rest when the heart rate is naturally slow.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Which specific gene (KCNQ1, KCNH2, or SCN5A) was identified in our family's genetic test?
  2. 2.Does my child have one copy (autosomal dominant) or two copies (autosomal recessive) of the mutation?
  3. 3.If my ECG is normal but I carry the gene, do I still need to avoid certain medications or follow safety protocols?
  4. 4.Should my child have a hearing test to rule out Jervell and Lange-Nielsen syndrome?
  5. 5.How does this specific mutation influence the choice of medication for us?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (17)
  1. 1

    CONGENITAL LONG QT SYNDROME: A SYSTEMATIC REVIEW.

    Galić E, Bešlić P, Kilić P, et al.

    Acta clinica Croatica 2021; (60(4)):739-748 doi:10.20471/acc.2021.60.04.22.

    PMID: 35734489
  2. 2

    Structures Illuminate Cardiac Ion Channel Functions in Health and in Long QT Syndrome.

    Brewer KR, Kuenze G, Vanoye CG, et al.

    Frontiers in pharmacology 2020; (11()):550 doi:10.3389/fphar.2020.00550.

    PMID: 32431610
  3. 3

    Molecular Pathophysiology of Congenital Long QT Syndrome.

    Bohnen MS, Peng G, Robey SH, et al.

    Physiological reviews 2017; (97(1)):89-134 doi:10.1152/physrev.00008.2016.

    PMID: 27807201
  4. 4

    Compound and heterozygous mutations of KCNQ1 in long QT syndrome with familial history of unexplained sudden death: Identified by analysis of whole exome sequencing and predisposing genes.

    Lin Y, Zhao T, He S, et al.

    Annals of noninvasive electrocardiology : the official journal of the International Society for Holter and Noninvasive Electrocardiology, Inc 2020; (25(1)):e12694 doi:10.1111/anec.12694.

    PMID: 31565860
  5. 5

    Mutation-Specific Differences in Kv7.1 (KCNQ1) and Kv11.1 (KCNH2) Channel Dysfunction and Long QT Syndrome Phenotypes.

    Kekenes-Huskey PM, Burgess DE, Sun B, et al.

    International journal of molecular sciences 2022; (23(13)) doi:10.3390/ijms23137389.

    PMID: 35806392
  6. 6

    Digenic heterozygous mutations of KCNH2 and SCN5A induced young and early-onset long QT syndrome and sinoatrial node dysfunction.

    Yang Z, Ma Y, Huang J, et al.

    Annals of noninvasive electrocardiology : the official journal of the International Society for Holter and Noninvasive Electrocardiology, Inc 2022; (27(1)):e12889 doi:10.1111/anec.12889.

    PMID: 34755423
  7. 7

    Precision medicine for long QT syndrome: patient-specific iPSCs take the lead.

    Yu Y, Deschenes I, Zhao MT

    Expert reviews in molecular medicine 2023; (25()):e5 doi:10.1017/erm.2022.43.

    PMID: 36597672
  8. 8

    Computational Study on Effect of KCNQ1 P535T Mutation in a Cardiac Ventricular Tissue.

    Satish H, Machireddy RR

    The Journal of membrane biology 2023; (256(3)):287-297 doi:10.1007/s00232-023-00287-9.

    PMID: 37166559
  9. 9

    Broad Electrocardiogram Syndromes Spectrum: From Common Emergencies to Particular Electrical Heart Disorders-Part II.

    Ceasovschih A, Balta A, Șorodoc V, et al.

    Diagnostics (Basel, Switzerland) 2025; (15(12)) doi:10.3390/diagnostics15121568.

    PMID: 40564888
  10. 10

    Electrocardiogram screening of deaf children for long QT syndrome: An Egyptian experience.

    Gouda S, Saif MQ, Shabana M, et al.

    Pacing and clinical electrophysiology : PACE 2018; (41(11)):1414-1419 doi:10.1111/pace.13484.

    PMID: 30132927
  11. 11

    Left cardiac sympathetic denervation in children with Jervell Lange-Nielsen syndrome and drug refractory torsades - A case series.

    Bhattacharya D, Namboodiri N, Sreelekshmi MP, et al.

    Pacing and clinical electrophysiology : PACE 2023; (46(10)):1197-1202 doi:10.1111/pace.14827.

    PMID: 37728293
  12. 12

    An International Multicenter Evaluation of Type 5 Long QT Syndrome: A Low Penetrant Primary Arrhythmic Condition.

    Roberts JD, Asaki SY, Mazzanti A, et al.

    Circulation 2020; (141(6)):429-439 doi:10.1161/CIRCULATIONAHA.119.043114.

    PMID: 31941373
  13. 13

    A case of congenital long QT syndrome, type 8, undergoing laparoscopic hysterectomy with general anesthesia.

    Chang SL, Chang CT, Hung WT, Chen LK

    Taiwanese journal of obstetrics & gynecology 2019; (58(4)):552-556 doi:10.1016/j.tjog.2019.05.031.

    PMID: 31307750
  14. 14

    Late-onset severe long QT syndrome.

    Asatryan B, Schaller A, Bartholdi D, Medeiros-Domingo A

    Annals of noninvasive electrocardiology : the official journal of the International Society for Holter and Noninvasive Electrocardiology, Inc 2018; (23(4)):e12517 doi:10.1111/anec.12517.

    PMID: 29194874
  15. 15

    Detection of distant relatedness in biobanks to identify undiagnosed cases of Mendelian disease as applied to Long QT syndrome.

    Lancaster MC, Chen HH, Shoemaker MB, et al.

    Nature communications 2024; (15(1)):7507 doi:10.1038/s41467-024-51977-4.

    PMID: 39209900
  16. 16

    Effect of age and gender on the QTc-interval in healthy individuals and patients with long-QT syndrome.

    Vink AS, Clur SB, Wilde AAM, Blom NA

    Trends in cardiovascular medicine 2018; (28(1)):64-75 doi:10.1016/j.tcm.2017.07.012.

    PMID: 28869094
  17. 17

    Transethnic Genome-Wide Association Study Provides Insights in the Genetic Architecture and Heritability of Long QT Syndrome.

    Lahrouchi N, Tadros R, Crotti L, et al.

    Circulation 2020; (142(4)):324-338 doi:10.1161/CIRCULATIONAHA.120.045956.

    PMID: 32429735

This page provides educational information about LQTS genetics and inheritance patterns. It does not replace professional medical advice from your cardiologist or genetic counselor.

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