Molecular stratification of arrhythmogenic mechanisms in the Andersen Tawil syndrome.

Andersen-Tawil syndrome (ATS) is a rare inheritable disease associated with loss-of-function mutations in KCNJ2, the gene coding the strong inward rectifier potassium channel Kir2.1, which forms an essential membrane protein controlling cardiac excitability. ATS is usually marked by a triad of periodic paralysis, life-threatening cardiac arrhythmias and dysmorphic features, but its expression is variable and not all patients with a phenotype linked to ATS have a known genetic alteration. The mechanisms underlying this arrhythmogenic syndrome are poorly understood. Knowing such mechanisms would be essential to distinguish ATS from other channelopathies with overlapping phenotypes and to develop individualized therapies. For example, the recently suggested role of Kir2.1 as a countercurrent to sarcoplasmic calcium reuptake might explain the arrhythmogenic mechanisms of ATS and its overlap with catecholaminergic polymorphic ventricular tachycardia. Here we summarize current knowledge on the mechanisms of arrhythmias leading to sudden cardiac death in ATS. We first provide an overview of the syndrome and its pathophysiology, from the patient's bedside to the protein and discuss the role of essential regulators and interactors that could play a role in cases of ATS. The review highlights novel ideas related to some post-translational channel interactions with partner proteins that might help define the molecular bases of the arrhythmia phenotype. We then propose a new all-embracing classification of the currently known ATS loss-of-function mutations according to their position in the Kir2.1 channel structure and their functional implications. We also discuss specific ATS pathogenic variants, their clinical manifestations, and treatment stratification. The goal is to provide a deeper mechanistic understanding of the syndrome toward the development of novel targets and personalized treatment strategies.

Andersen-Tawil syndrome: deep phenotyping reveals significant cardiac and neuromuscular morbidity.

Andersen-Tawil syndrome is a neurological channelopathy caused by mutations in the KCNJ2 gene that encodes the ubiquitously expressed Kir2.1 potassium channel. The syndrome is characterized by episodic weakness, cardiac arrythmias and dysmorphic features. However, the full extent of the multisystem phenotype is not well described. In-depth, multisystem phenotyping is required to inform diagnosis and guide management. We report our findings following deep multimodal phenotyping across all systems in a large case series of 69 total patients, with comprehensive data for 52. As a national referral centre, we assessed point prevalence and showed it is higher than previously reported, at 0.105 per 100 000 population in England. While the classical phenotype of episodic weakness is recognized, we found that a quarter of our cohort have fixed myopathy and 13.5% required a wheelchair or gait aid. We identified frequent fat accumulation on MRI and tubular aggregates on muscle biopsy, emphasizing the active myopathic process underpinning the potential for severe neuromuscular disability. Long exercise testing was not reliable in predicting neuromuscular symptoms. A normal long exercise test was seen in five patients, of whom four had episodic weakness. Sixty-seven per cent of patients treated with acetazolamide reported a good neuromuscular response. Thirteen per cent of the cohort required cardiac defibrillator or pacemaker insertion. An additional 23% reported syncope. Baseline electrocardiograms were not helpful in stratifying cardiac risk, but Holter monitoring was. A subset of patients had no cardiac symptoms, but had abnormal Holter monitor recordings which prompted medication treatment. We describe the utility of loop recorders to guide management in two such asymptomatic patients. Micrognathia was the most commonly reported skeletal feature; however, 8% of patients did not have dysmorphic features and one-third of patients had only mild dysmorphic features. We describe novel phenotypic features including abnormal echocardiogram in nine patients, prominent pain, fatigue and fasciculations. Five patients exhibited executive dysfunction and slowed processing which may be linked to central expression of KCNJ2. We report eight new KCNJ2 variants with in vitro functional data. Our series illustrates that Andersen-Tawil syndrome is not benign. We report marked neuromuscular morbidity and cardiac risk with multisystem involvement. Our key recommendations include proactive genetic screening of all family members of a proband. This is required, given the risk of cardiac arrhythmias among asymptomatic individuals, and a significant subset of Andersen-Tawil syndrome patients have no (or few) dysmorphic features or negative long exercise test. We discuss recommendations for increased cardiac surveillance and neuropsychometry testing.

Failure of radiofrequency catheter ablation and success of flecainide to suppress premature ventricular contractions in Andersen-Tawil syndrome: A case report.

This case report presents a 33-year-old woman with premature ventricular contractions (PVCs). Her genetic testing was positive for KCNJ2 missense mutation at chr17:68171832;NM_000891.2. This mutation was compatible with Andersen-Tawil syndrome. We made an electrophysiological study to determine origin of PVCs however at endocardial mapping there was not any focus of PVC and at epicardial mapping we ablated low voltage areas in the inferior segments of both ventricles. She was discharged with flecainide and metoprolol therapy. After 3 months, her PVC burden was significantly decreased at Holter monitoring.

Obstetric management of a patient with Andersen-Tawil syndrome: A case report.

Andersen-Tawil syndrome (ATS) is a rare hereditary long QT syndrome type 7 caused by a missense mutation in the KCNJ2 gene. ATS is characterized by ventricular arrhythmia, periodic limb paralysis and minor external malformations. Although only three reports of pregnant women with Andersen-Tawil syndrome have been reported to date, no exacerbation of ventricular arrhythmia was observed from pre-partum to delivery in all cases compared to that before pregnancy, and it was suggested that the risk of arrhythmic events from pre-partum to delivery is not high. Unlike these previous reports, we herein present a case of Andersen-Tawil syndrome in which ventricular arrhythmias increased and sustained ventricular tachycardia was developed during labor progression. We also advise caution that pregnant patients with Andersen-Tawil syndrome may have varying times of exacerbation of the arrhythmia, and ventricular arrhythmias may be associated with painful uterine contractions.

Natural History and Risk Stratification in Andersen-Tawil Syndrome Type 1.

BACKGROUND: Andersen-Tawil Syndrome type 1 (ATS1) is a rare arrhythmogenic disorder, caused by loss-of-function mutations in the KCNJ2 gene. We present here the largest cohort of patients with ATS1 with outcome data reported. OBJECTIVES: This study sought to define the risk of life-threatening arrhythmic events (LAE), identify predictors of such events, and define the efficacy of antiarrhythmic therapy in patients with ATS1. METHODS: Clinical and genetic data from consecutive patients with ATS1 from 23 centers were entered in a database implemented at ICS Maugeri in Pavia, Italy, and pooled for analysis. RESULTS: We enrolled 118 patients with ATS1 from 57 families (age 23 ± 17 years at enrollment). 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. An increased risk of LAE was associated with a history of syncope (hazard ratio [HR]: 4.54; p = 0.02), with the documentation of sustained ventricular tachycardia (HR 9.34; p = 0.001) and with the administration of amiodarone (HR: 268; p < 0.001). The rate of LAE without therapy (1.24 per 100 person-years [py]) 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). CONCLUSIONS: Our data demonstrate that the clinical course of patients with ATS1 is characterized by a high rate of LAE. A history of unexplained syncope or of documented sustained ventricular tachycardia is associated with a higher risk of LAE. Amiodarone is proarrhythmic and should be avoided in patients with ATS1.

Therapeutic management of ventricular arrhythmias in Andersen-Tawil syndrome.

Andersen-Tawil Syndrome (ATS) is a rare periodic paralysis with typical skeletal and neuromuscular features. Cardiac involvement may range from asymptomatic ventricular arrhythmias to sudden death. Its management remains challenging and the choice between antiarrhythmic drug therapy and implantable cardioverter defibrillator (ICD) is not simple. We present a case of ATS patient with episodes of bidirectional ventricular tachycardia, well controlled by flecainide therapy initially, which in particular conditions of fever and hypokaliemia had a cardiac arrest with ventricular fibrillation, with neurological sequelae and need of an ICD implant. A review of the therapeutic management of this disease is presented.

Review of the Diagnosis and Treatment of Periodic Paralysis.

Periodic paralyses (PPs) are rare neuromuscular disorders caused by mutations in skeletal muscle sodium, calcium, and potassium channel genes. PPs include hypokalemic paralysis, hyperkalemic paralysis, and Andersen-Tawil syndrome. Common features of PP include autosomal dominant inheritance, onset typically in the first or second decades, episodic attacks of flaccid weakness, which are often triggered by diet or rest after exercise. Diagnosis is based on the characteristic clinic presentation then confirmed by genetic testing. In the absence of an identified genetic mutation, documented low or high potassium levels during attacks or a decrement on long exercise testing support diagnosis. The treatment approach should include both management of acute attacks and prevention of attacks. Treatments include behavioral interventions directed at avoidance of triggers, modification of potassium levels, diuretics, and carbonic anhydrase inhibitors. Muscle Nerve 57: 522-530, 2018.

Novel mutation in the KCNJ2 gene is associated with a malignant arrhythmic phenotype of Andersen-Tawil syndrome.

BACKGROUND: Andersen-Tawil syndrome (ATS) is a rare inherited multisystem disorder associated with mutations in KCNJ2 and low prevalence of life-threatening ventricular arrhythmias. Our aim was to describe the clinical course of ATS in a family, in which the proband survived aborted cardiac arrest (ACA) and genetic screening revealed a previously unknown mutation (c.271_282del12[p.Ala91_Leu94del]) in the KCNJ2 gene. METHODS: A cascade family screening was performed in a 5-generation family after identification of the KCNJ2 mutation in the proband. Subsequently, 10 of 21 screened individuals appeared to be mutation carriers (median age 38 [range 10-75] years, 3 female). Mutation carriers underwent clinical examination including biochemistry panel, cardiac ultrasound, Holter ECG, and exercise stress test. RESULTS: (1) At baseline, 2 patients had survived ACA, 3 had syncope or presyncopal attacks, and 2 reported palpitations. Exercise-induced nonsustained bidirectional ventricular tachycardia was documented in 4 patients, 2 received implantable cardioverter-defibrillators (ICD) for primary prevention and 2 for secondary prevention. (2) During follow-up, 1 primary prevention and 1 secondary prevention patient received in total 4 adequate ICD shocks. Life-threatening ventricular arrhythmias were documented during childhood in 5 of 10 mutation carriers. (3) All mutation carriers presented with characteristic mild dysmorphic features. Only 1 patient suffered from periodic paralysis. All had normal serum potassium level at repeated assessments and none had any other extracardiac disease manifestation. CONCLUSION: Our findings suggest that the novel KCNJ2 mutation is associated with a predominantly cardiac phenotype of Andersen-Tawil syndrome with high propensity to life-threatening ventricular arrhythmias presenting from childhood and young adulthood.

Cardiac characteristics and long-term outcome in Andersen-Tawil syndrome patients related to KCNJ2 mutation.

AIMS: Andersen-Tawil syndrome (ATS) is an uncommon form of channelopathy linked to mutations in the KCNJ2 gene. Currently, little is known about the long-term arrhythmic prognosis of this disease. METHODS AND RESULTS: We conducted a retrospective multicentre study in nine French hospitals. Patients were recruited only if they were KCNJ2 mutation carriers. Thirty-six patients (female n = 22, 61%) from 20 unrelated kindred were included with a mean follow-up of 9.5 ± 8.2 years. We found 12 distinct KCNJ2 mutations in the 20 probands. Three of them were novel. Thirteen patients (36%) experienced syncope and one patient was resuscitated from cardiac arrest before diagnosis. The mean QTc interval was 439 ± 57 ms and QUc was 642 ± 64 ms. All patients had normal ejection fraction. Holter recordings in 33 patients found 11 272 premature ventricular complexes (PVCs) per day on average, 25 patients had episodes of bigeminy, and 25 patients had polymorphic PVCs. Twenty-three patients (70%) had non-sustained polymorphic ventricular tachycardia (VT), and six sustained polymorphic VT. Only one patient presented with torsades de pointes. Patients were treated with beta-blocker (n = 20), beta-blocker and amiodarone (n = 2), beta-blocker and flecainide (n = 6), or acetazolamide (n = 6). Radiofrequency ablation was attempted in five patients without clinical success. An implantable cardiac defibrillator was implanted in three patients. During follow-up, none of the patients died, four patients experienced syncope under treatment, and one patient had non-fatal cardiac arrest. CONCLUSION: Despite a severe clinical presentation with a very high rate of ventricular arrhythmias, the arrhythmic prognosis of the ATS patients is relatively good under treatment.

Andersen-Tawil syndrome: clinical and molecular aspects.

Andersen­Tawil syndrome (ATS) is a rare hereditary multisystem disorder. Ventricular arrhythmias, periodic paralysis and dysmorphic features constitute the classic triad of ATS symptoms. The expressivity of these symptoms is, however, extremely variable, even within single ATS affected families, and not all ATS patients present with the full triad of symptoms. 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. In ATS type 1 (ATS1), the syndrome is associated with a loss-of-function mutation in the KCNJ2 gene,which encodes the Kir2.1 inward rectifier potassium channel. In ATS type 2 (ATS2), which does not differ from ATS1 in its clinical symptoms, the genetic defect is unknown. Consequently, ATS2 comprises all cases of ATS in which genetic testing did not reveal a mutation in KCNJ2. 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. In this review, we summarize the clinical symptoms, the underlying genetic and molecular defects, and the management and treatment of ATS.

Andersen-Tawil syndrome associated with aborted sudden cardiac death: atrial pacing was effective for ventricular arrhythmias.

A 37-year-old Japanese woman experienced aborted sudden cardiac death from ventricular fibrillation and was diagnosed with Andersen-Tawil syndrome by genetic analysis that revealed 2 mutations in the KCNJ2 gene. Although she received an implantation of implantable cardioverter defibrillator and beta-blocker therapy, the frequency of premature ventricular contraction and bidirectional ventricular tachycardia did not decrease. Her ventricular arrhythmias increased after a full stomach test and a neostigmine provocation test, and reduced after cibenzoline administration, which indicates the relation with vagal tone. Moreover, increasing the pacing rate significantly decreased them. These findings indicate that the arrhythmia was bradycardia-dependent in this case.

The Twiddling Andersen.

Andersen-Tawil syndrome is an autosomal dominant condition characterized by dysmorphic features, periodic paralysis, and ventricular arrhythmias. Twiddler syndrome is characterized by intentional or inadvertent manipulation of implanted devices in the pacemaker pocket. We describe an unusual case of an 8-year-old girl who had both syndromes.

Andersen-Tawil syndrome: management challenges during pregnancy, labor, and delivery.

Andersen-Tawil syndrome (ATS) is characterized by ventricular arrhythmias, hypokalemic periodic paralysis and developmental anomalies. It is caused by mutations in the KCNJ2 gene that encodes for the alpha-subunit of Kir2.1, a K(+) channel responsible for cardiac repolarization. Providing effective therapy to reduce arrhythmia burden and risk of sudden death is challenging, especially in the context of pregnancy and childbirth. We report a case of a pregnant 27-year-old woman with an R218W mutation in the C-terminal interaction domain of KCNJ2 causing ATS. Regular cardiac and obstetric assessments were performed for the duration of the pregnancy, which carried to term and delivered successfully with potassium replacement and intravenous beta blockade. ATS is a rare and potentially lethal condition in which there is considerable genetic and phenotypic heterogeneity. Effective management strategies are directed at reducing symptoms, arrhythmia burden and sudden cardiac death. This case illustrates the challenges and approach to management of patients with ATS who are pregnant and undergo childbirth.