In a 7-year-old boy with normal hearing suffering from repeated syncope an 
extremely prolonged QTc interval (up to 700 ms) was found. The mother was 
completely asymptomatic and the father had an intermittently borderline QTc 
interval (maximum 470 ms) but no symptoms. In the proband a mutation analysis of 
KCNQ1 gene revealed a homozygous 1893insC mutation. The parents were 
heterozygous for this mutation. There was no consanguineous marriage in the 
family. The clinical relevance of these findings is that apparently normal 
individuals may have a latent reduction of repolarizing currents, a "reduced 
repolarization reserve," because they are carriers of latent ion channel genes 
mutations.