| Résumé : | Initial Posting: November 22, 2004; Last Update: June 7, 2018.
Clinical characteristics.
Andersen-Tawil syndrome (ATS) is characterized by a triad of: episodic flaccid muscle weakness (i.e., periodic paralysis); ventricular arrhythmias and prolonged QT interval; and anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis. 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. Mild permanent weakness is common. Mild learning difficulties and a distinct neurocognitive phenotype (i.e., deficits in executive function and abstract reasoning) have been described.
Diagnosis/testing.
The diagnosis of ATS is established in an individual with characteristic clinical and ECG findings and/or identification of a pathogenic variant in KCNJ2.
Management.
Treatment of manifestations: For episodic weakness: if serum potassium concentration is low (
Prevention of primary manifestations: 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; implantable cardioverter-defibrillator for those with tachycardia-induced syncope. Empiric treatment with flecainide should be considered for significant, frequent ventricular arrhythmias in the setting of reduced left ventricular function.
Prevention of secondary complications: Cautious use of antiarrhythmic drugs (particularly class I drugs) that may paradoxically exacerbate the neuromuscular symptoms.
Surveillance: Annual screening of asymptomatic individuals with a KCNJ2 pathogenic variant with a 12-lead ECG and 24-hour Holter monitoring.
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).
Evaluation of relatives at risk: Molecular genetic testing if the pathogenic variant is known; if not, detailed neurologic and cardiologic evaluation, 12-lead ECG, and 24-hour Holter monitoring to reduce morbidity and mortality through early diagnosis and treatment of at-risk relatives.
Genetic counseling.
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. Each child of an individual with ATS has a 50% chance of inheriting the disorder. Prenatal diagnosis for pregnancies at increased risk is possible if the KCNJ2 pathogenic variant has been identified in an affected family member. |
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