This study aimed to identify mutations in the genes KVLQT1, HERG, SCN5A, KCNE1, and KCNE2, which are associated with Long-QT Syndrome (LQTS), a cardiovascular disorder characterized by a prolonged QT interval on ECG and symptoms such as syncope, seizures, and sudden death. The researchers screened 262 unrelated individuals with LQTS for mutations in these genes using mutational analyses. They identified 134 new mutations, bringing the total number of identified mutations to 177 (68% of the population). KVLQT1 and HERG accounted for 87% of the mutations, with missense mutations being the most common type. Most mutations were found in intracellular and transmembrane domains, and 78% of the mutations were identified in single families or individuals. The findings will facilitate genotype-phenotype studies and improve presymptomatic diagnosis and therapy for LQTS.This study aimed to identify mutations in the genes KVLQT1, HERG, SCN5A, KCNE1, and KCNE2, which are associated with Long-QT Syndrome (LQTS), a cardiovascular disorder characterized by a prolonged QT interval on ECG and symptoms such as syncope, seizures, and sudden death. The researchers screened 262 unrelated individuals with LQTS for mutations in these genes using mutational analyses. They identified 134 new mutations, bringing the total number of identified mutations to 177 (68% of the population). KVLQT1 and HERG accounted for 87% of the mutations, with missense mutations being the most common type. Most mutations were found in intracellular and transmembrane domains, and 78% of the mutations were identified in single families or individuals. The findings will facilitate genotype-phenotype studies and improve presymptomatic diagnosis and therapy for LQTS.