Long QT syndrome is one of the most common cardiac ion channel diseases, but its 
morbidity and mortality rate can be lessened with an early diagnosis and proper 
treatment. This cardiac ventricular repolarization abnormality is characterized 
by a prolonged QT interval and a propensity for ventricular tachycardia (VT) of 
the torsades de pointes type. The long QT syndrome represents a high risk for 
presyncope, syncope, cardiac arrest, and sudden death. Jervell and Lange-Nielsen 
syndrome (JLNS) is a recessively inherited form of long QT syndrome 
characterized by profound sensorineural deafness and prolongation of the QT 
interval. Findings have shown that JLNS occurs due to homozygous and compound 
heterozygous pathogenic variants in KCNQ1 or KCNE1. A 3.5-year-old girl 
presented to the hospital with recurrent syncope, seizures, and congenital 
sensorineural deafness. Her electrocardiogram showed a markedly prolonged QT 
interval, and she had a diagnosis of JLNS. The sequence analysis of the proband 
showed the presence of a pathogenic homozygous missense variant (c.728G>A, 
p.Arg243His). Heterozygous mutations of KCNQ1 were identified in her mother, 
father, and sister, demonstrating true homozygosity. Even with high-dose 
beta-blocker therapy, the patient had two VT attacks, so an implantable 
cardioverter defibrillator was fitted. The authors suggest early genetic 
diagnosis for proper management of the disease in the proband and genetic 
counseling for both the proband and the girl's extended family.