Neonatal long QT syndrome due to a de novo dominant negative hERG mutation.

A 4-day-old girl with ventricular tachyarrhythmias, sinus bradycardia, and 2:1 atrioventricular block had prolongation of the QT interval. She was symptomatic with arching, gasping, and cyanosis presumably due to a life-threatening ventricular tachyarrhythmia such as torsades de pointes. Molecular genetic studies indicated a heterozygous, de novo, dominant negative mutation in hERG, a gene that encodes a protein in a potassium ion channel. The parents do not have the mutation. The patient's clinical scenario was produced by the convergence of 3 events: a de novo mutation occurred in hERG, the mutation was dominant negative, and the action of the mutation resulted in neonatal long QT syndrome. The child was treated aggressively and is doing well at age 6 years.