We present the case of a twin pregnancy of heterozygous andhomozygous long QT syndrome (LQTS) type 1 (LQT1)genotype, referred because of in utero bradycardia in thehomozygous twin at 19 weeks of gestation, with follow-upuntil.12 months of age. Fetal heart rate may predict bothgenotype and disease severity, as previously shown in2 LQTS founder populations.1This unique case report is acomparison of fetal heart rate and clinical outcome in twinprobands of heterozygous and homozygous genotype, in afamily without prior diagnosis of LQTS. In this setting, wediscuss the early management of LQTS and Jervell andLange-Nielsen syndrome (JLNS) detected in utero.