SummaryLong QT syndrome (LQTS) has great genetic heterogeneity: more than 500 mutations have been described in several genes. Despite many advances, a genetic diagnosis still cannot be established in 25-30% of patients. The aim of the present study was to perform genetic evaluation in 9 Russian families with LQTS; here we report the results of 4 positive probands and their relatives (a total of 16 individuals). All subjects underwent clinical examination, 12-lead ECG, and Holter monitoring. Genetic analysis of the 14 genes mainly involved in LQTS was performed using a next-generation sequencing approach. We identified two new mutations (KCNQ1 gene) and 6 known mutations (AKAP9, ANK2, KCNE1 and KCNJ2 genes) in 4 out of 9 probands, some of which have already been described in association with LQTS. Segregation studies suggest a possible causative role for KCNQ1 p.(Leu342Pro), AKAP9 p.(Arg1609Lys), KCNE1 p.(Asp85Asn), and KCNJ2 p.(Arg82Gln) variations. Our study confirmed the high genetic heterogeneity of this disease and highlights the difficulties to reveal clear pathogenic genotypes also in large pedigrees. To the best of our knowledge, this is the first genetic study of LQTS patients from Russian families. (Int Heart J 2017; 58: 81-87)

Aim To assess the diagnostic accuracy of long QT syndrome in children and to estimate the results of the follow-up.Methods High-risk groups of children with bradycardia less than the second percentile and/or a family history of sudden death syndrome, and children with syncope diagnosed with the ECG testing were included in the study. All patients underwent routine medical examination, molecular genetic testing and were followed-up for 3,5–10 years.Results The majority of children haves transient corrected QT prolongation secondary to therapy, requiring ECG monitoring. High-risk group screening reports higher rates of idiopathic LQTS. ECG testing shows its efficiency among asymptomatic children with a normal heart rate. Patients present with syncope at the outpatient settings require the exclusion of a wide range of diseases, both congenital and acquired heart disease. The clinical status of the examined patients does not always correspond to the known LQTS variants. Molecular genetic analysis provides relevant information on the genetic heterogeneity of the disease, including new mutations, both pathological and beneficial ones.Conclusion Regardless of the presence or absence of molecular genetic confirmation of LQTS, beta blocker therapy in some cases combined with implanted cardioverterdefibrillator prevents the development of the adverse events in the long-term period and ensures normal emotional, intellectual and physical development.