The IKs current (slow delayed rectifier potassium current) is encoded by KCNQ1 (KvLQT1) + KCNE1 (minK). Loss-of-function mutation in KCNQ1 leads to which specific consequence on the cardiac action potential and which syndrome?

• A Shortened QT interval; Brugada syndrome
• B Prolonged PR interval; Wolff-Parkinson-White syndrome
• C Widened QRS complex; arrhythmogenic right ventricular cardiomyopathy
• D Prolonged QT interval; Romano-Ward syndrome (LQT1) ✓

Explanation

IKs is a major repolarizing current; its reduction delays phase 3 repolarization, prolonging the action potential duration and the QT interval on ECG. Mutations in KCNQ1 (encoding the alpha subunit) cause LQT1, the most common form of Romano-Ward syndrome (autosomal dominant congenital long QT syndrome). Patients are especially vulnerable to adrenergic stress (exercise, emotion-triggered arrhythmias), making beta-blockers the primary therapy.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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