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Long QT syndrome type 2
LQTS2 affects the heart's electrical system, potentially leading to fast, chaotic heartbeats (arrhythmias) that can cause fainting, seizures, or sudden cardiac arrest. It is one of the most common forms of inherited Long QT syndrome, typically caused by changes in the KCNH2 gene.
Overview
Long QT syndrome type 2 (LQTS2) is a specific form of an inherited heart condition known as Long QT syndrome. This condition affects the heart's electrical activity, specifically the 'repolarisation' phase, when the heart muscle cells reset themselves after each beat. In LQTS2, this resetting takes longer than usual, which can be seen as a prolonged 'QT interval' on an electrocardiogram (ECG) [PMID:33606361]. This delay can make the heart more susceptible to developing dangerous, fast, and irregular heart rhythms, called arrhythmias. These arrhythmias can sometimes be life-threatening.
LQTS2 is a genetic condition, meaning it is passed down through families. It is caused by changes in specific genes, most commonly KCNH2. While some individuals with LQTS2 may experience severe symptoms, others might have only mild symptoms or none at all, despite having the genetic change. The condition affects approximately 1 in 5,000 people, making it one of the more frequently diagnosed forms of Long QT syndrome.
Understanding LQTS2 is important for affected individuals and their families. Early diagnosis and appropriate management can significantly reduce the risk of serious complications. Management often involves lifestyle adjustments, medication, and, in some cases, device implantation, all tailored to the individual's specific needs and risk profile.
Symptoms & clinical features
The symptoms of Long QT syndrome type 2 (LQTS2) can vary significantly among individuals, even within the same family. Some people might experience no symptoms, while others may have recurrent and severe episodes. The most common symptoms are related to abnormal heart rhythms (arrhythmias) which can lead to reduced blood flow to the brain.
Typical symptoms include fainting spells (syncope), particularly in response to sudden loud noises, strong emotions, or physical exercise. These fainting episodes can sometimes be accompanied by seizures, which can be mistaken for epilepsy. In severe cases, LQTS2 can lead to a life-threatening arrhythmia called Torsades de Pointes, which can progress to ventricular fibrillation and sudden cardiac arrest [PMID:33606361].
Unlike some other forms of Long QT syndrome, individuals with LQTS2 are particularly sensitive to auditory stimuli, such as alarm clocks or phone ringing. Stress and sleep can also be triggers for cardiac events in some cases. Recognising these specific triggers can be an important part of managing the condition.
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Affected organs
Long QT syndrome type 2 primarily affects the heart, specifically its electrical system. The condition leads to a disruption in the normal flow of electrical signals that coordinate the heart's pumping action. This electrical disturbance results in a prolonged 'QT interval' on an ECG, reflecting a delay in the heart muscle cells' ability to repolarise, or recharge, after each beat.
There are no structural abnormalities of the heart muscle or other organs directly caused by LQTS2. The problem lies solely within the electrical functioning of the heart. However, the consequences of this electrical dysfunction, such as arrhythmias, can indirectly affect other organs, particularly the brain, due to temporary reductions in blood supply during fainting episodes or more serious events.
Risks & severity
The severity of Long QT syndrome type 2 (LQTS2) can vary widely, from individuals who are completely asymptomatic to those who experience life-threatening cardiac events. The risk of cardiac events, such as fainting or sudden cardiac arrest, is not uniform and can be influenced by specific genetic changes, gender, and environmental triggers [PMID:33606361].
Women with LQTS2, particularly during the postpartum period, may have a higher risk of cardiac events [PMID:33606361]. Certain medications that can further prolong the QT interval should generally be avoided by individuals with LQTS2, as they can increase the risk of arrhythmias. Triggers such as sudden loud noises, emotional stress, and strenuous exercise are also important considerations in managing the condition.
While LQTS2 is present from birth, the age of onset for symptoms is highly variable. Some individuals may experience their first symptoms during childhood or adolescence, while others may not develop symptoms until adulthood, or even remain asymptomatic throughout their lives. Regular monitoring and appropriate management are crucial for reducing the lifetime risk of serious complications.
Genetic causes
Long QT syndrome type 2 (LQTS2) is predominantly caused by pathogenic variants in the *KCNH2* gene. This gene provides instructions for making a protein that is a key component of a potassium channel in the heart called the hERG (human Ether-à-go-go-Related Gene) channel. These channels are crucial for the heart's electrical system, playing a vital role in the 'repolarisation' phase of the cardiac action potential, which is when the heart muscle cells reset after each beat.
When a pathogenic variant occurs in *KCNH2*, the hERG channel may not function correctly or may not be produced in sufficient quantities. This leads to a reduction in the normal outflow of potassium ions from the heart cells, prolonging the repolarisation process. This extended repolarisation is what causes the characteristic long QT interval seen on an ECG [PMID:33606361].
The impaired function of the hERG channel makes the heart more prone to developing erratic and potentially dangerous electrical activity, increasing the risk of arrhythmias. While *KCNH2* variants are the most common cause of LQTS2, research is ongoing into other potential genetic factors that may influence the condition's presentation and severity.
- KCNH2 potassium voltage-gated channel subfamily H member 2The KCNH2 gene provides instructions for making a potassium channel protein crucial for regulating the electrical activity of heart muscle cells, maintaining a regular heart rhythm.
Inheritance pattern
Long QT syndrome type 2 (LQTS2) is inherited in an autosomal dominant pattern. This means that a person only needs to inherit one copy of the altered gene, from either parent, to develop the condition. If one parent has LQTS2, there is a 50% chance with each pregnancy that their child will also inherit the altered gene and therefore have LQTS2. This chance is the same for sons and daughters.
Individuals who inherit the altered gene may experience varying degrees of symptoms, or they may never develop symptoms at all. This phenomenon is known as variable expressivity. Therefore, even if a parent has a mild form of the condition, their child could have a more severe form, or vice-versa.
It is also possible for LQTS2 to arise from a new (de novo) genetic change in an individual, meaning neither parent carries the altered gene. However, once a person has such a change, they can then pass it on to their children in an autosomal dominant manner. Genetic counselling is often recommended for affected individuals and their families to understand the inheritance patterns and risks.
Each child has a 50% chance of inheriting the pathogenic variant, regardless of sex.
Diagnosis & testing
Diagnosing Long QT syndrome type 2 (LQTS2) typically begins with a review of an individual's personal and family medical history, looking for symptoms such as unexplained fainting, seizures, or sudden cardiac arrest. The primary diagnostic tool is an electrocardiogram (ECG), which measures the electrical activity of the heart. A prolonged QT interval on an ECG is a key indicator of Long QT syndrome [PMID:33606361].
If an ECG suggests Long QT syndrome, further tests may be performed, including Holter monitoring (a portable ECG that records heart activity over 24-48 hours), exercise stress tests, and sometimes tilt table tests. A definitive diagnosis of LQTS2 is confirmed through genetic testing, which looks for pathogenic variants in genes like *KCNH2*. In the UK, genetic testing for inherited cardiac conditions, including LQTS2, is available through the NHS Genomic Medicine Service (GMS) pathways. Referrals for testing are typically made by cardiologists or clinical geneticists, and are linked to specific R-codes for diagnostic or predictive testing. Genetic counselling services are available to help individuals and families understand the testing process and implications of the results.
Management & lifestyle
Managing Long QT syndrome type 2 (LQTS2) focuses on reducing the risk of life-threatening arrhythmias and improving quality of life. The specific management plan is individualised, based on symptoms, ECG findings, genetic test results, and personal risk factors. It is essential to work closely with a cardiologist specialising in inherited heart conditions.
Medication, typically beta-blockers, is a cornerstone of management for many individuals with LQTS2. These medications help to stabilise the heart's electrical activity and reduce the likelihood of arrhythmias. Lifestyle modifications are also important, including avoiding strenuous exercise, sudden loud noises, and emotional stress if these are known triggers. A list of medications known to prolong the QT interval should also be avoided, and individuals should always consult their healthcare professional before taking new medicines.
For individuals at high risk of cardiac events, an implantable cardioverter-defibrillator (ICD) may be considered. An ICD is a small device surgically placed under the skin that can detect dangerous arrhythmias and deliver an electrical shock to restore a normal heart rhythm. Regular follow-up appointments with a cardiologist are crucial to monitor the condition and adjust the management plan as needed within the NHS care pathway. Genetic counsellors can provide support and information to individuals and families regarding the condition and its implications.
UK care pathway
In the UK, individuals suspected of having Long QT syndrome type 2 (LQTS2) or with a confirmed diagnosis will typically be managed within the NHS Genomic Medicine Service (GMS) pathways. Referral to a clinical genetics service or a specialist inherited cardiac conditions clinic is a common starting point. These clinics bring together cardiologists, geneticists, and genetic counsellors to provide comprehensive care.
Genetic testing for LQTS2, often involving the *KCNH2* gene, is available through the GMS and is usually requested by a specialist using relevant R-codes for diagnostic or predictive testing. Following diagnosis, care typically involves regular cardiology follow-ups, medication management, and lifestyle advice. Genetic counsellors play a vital role in explaining the inheritance pattern, implications for family members, and supporting individuals through the genetic testing process and beyond.
Frequently asked questions
What activities should someone with LQTS2 avoid?
Individuals with LQTS2 are typically advised to avoid strenuous exercise, sudden loud noises (like alarm clocks), and situations that cause extreme emotional stress, as these can trigger dangerous arrhythmias. Your cardiologist will provide specific guidance tailored to your individual risk profile.
Can I have children if I have LQTS2?
Yes, individuals with LQTS2 can have children. However, because LQTS2 is inherited in an autosomal dominant pattern, there is a 50% chance with each pregnancy that your child will also inherit the condition. Genetic counselling can help you understand these risks and discuss reproductive options.
Are there any medications I should avoid if I have LQTS2?
Yes, many medications can prolong the QT interval and should be avoided by individuals with LQTS2, as they can increase the risk of arrhythmias. It is crucial to always inform any healthcare professional prescribing medication that you have LQTS2. Your cardiologist or pharmacist can provide a list of drugs to avoid.
How often do I need to see a doctor for LQTS2?
Regular follow-up appointments with a cardiologist specialising in inherited heart conditions are essential for individuals with LQTS2. The frequency of these appointments will depend on your symptoms, risk factors, and overall management plan, but typically involves annual reviews.
Is LQTS2 the same as 'sudden adult death syndrome'?
Long QT syndrome type 2 is an underlying cause for some cases of Sudden Arrhythmic Death Syndrome (SADS), sometimes informally referred to as 'sudden adult death syndrome'. SADS refers to unexpected deaths due to cardiac arrest in individuals where no obvious cause is found post-mortem, and inherited conditions like LQTS2 are often implicated.
References
- Cox KO, Wang BX. Long QT syndrome type 2: mechanism-based therapies. Future cardiology. 2021. PMID: 33739161
- Crotti L, Neves R, Dagradi F. Therapeutic Efficacy of Mexiletine for Long QT Syndrome Type 2: Evidence From Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes, Transgenic Rabbits, and Patients. Circulation. 2024. PMID: 38939955
- Singh V, Wagner KT, Williams LG. Knock-in Kcnh2 Rabbit Model of Long QT Syndrome Type-2, Epilepsy, and Sudden Death. bioRxiv : the preprint server for biology. 2024. PMID: 39763998
- Smith JL, Anderson CL, Burgess DE. Molecular pathogenesis of long QT syndrome type 2. Journal of arrhythmia. 2016. PMID: 27761161
- Singh V, Wagner KT, Williams LG. Knock-in Kcnh2 rabbit model of long QT syndrome type-2, epilepsy, and sudden death. Journal of translational medicine. 2025. PMID: 40234944
- Ono M, Burgess DE, Schroder EA. Long QT Syndrome Type 2: Emerging Strategies for Correcting Class 2 KCNH2 (hERG) Mutations and Identifying New Patients. Biomolecules. 2020. PMID: 32759882
- Pan Z, Fu Q, Jiang H. Computational analysis of long QT syndrome type 2 and the therapeutic effects of KCNQ1 antibodies. Digital health. 2024. PMID: 39484649
- Foo B, Williamson B, Young JC. hERG quality control and the long QT syndrome. The Journal of physiology. 2016. PMID: 26718903