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The primary long QT syndrome (LQTS) is hereditary disorder of cardiac rhythm. More than 15 genetic types of the disease known. Most prevalent is the type of the disorder related to potassium channel KvLQT1.Aim. Analysis of mutation spectrum in the gene KCNQ1, coding α-subunit of potassium channel IKs, collected with specimens of 143 families with LQTS.Material and methods. Clinical part of the study and LQTS diagnostics included a standard range of personal and family histore, ECG, 24-hour Holter monitoring, EchoCG, long-time passive orthostatic test (tilt-test) if indicated. DNA-diagnostics of mutations in the gene KCNQ1 was performed with the method of direct authomatic sequencing by Sanger.Results. LQTS, type 1, was verified in 53 families (37%). There were 39 mutations revealed in the gene KCNQ1. Most mutations were found once per family, only 4 mutations repeated in 3 or more non-related families. Most prevalent mutation c.477+1G>A in heterozygous kind presents with milder course of the disease. Second by prevalence mutation replacement p.A341V points on serious prognosis of the disease and might be regarded as genetic factor of SCD. Relative predominance of mutations was found for exones 2, 5, 6, 7, 8 of gene KCNQ1. About 20% of mutations appeared de novo. Two non-related mutations were found in 5 families (3,5%) probands. In all cases the carriers of two mutations the disease had worse course, than in one mutation carriage.Conclusion. The data on genetic nature of the disease and clinical signs of various mutations in LQTS can be applied for planning of dynamic follow-up and tactics of antiarrhythmic therapy.

Aim. To complete DNA-diagnostics for the patients with syncopes and not showing clinically significant rhythm disorders, but with family anamnesis of sudden death. Material and methods. Clinical case. The patient 22 y.o. consulted at RSCS n.a.Petrovsky with the primary diagnosis of "inherited epilepsy" and complaints on presyncopes and dizziness. During examination there was no data found to prove the inherited epilepsy and clinically significant rhythm disorders. Taking into account the family anamnesis of sudden death a dignosis of "idiopathic ventricular tachycardia" was suggested and the patient underwent two-chamber rate-adaptive cardioverter-defibrillator Maximo II DR D284DRG implantation. DNA-testing revealed a mutation of p.R583H in the gene KCNQ1, that had been previously described as probable to cause type 1 long-QT-syndrome. During the next 12 month after implantation there were 2 proven strobes recorded. The patient was consulted by cardiologist to prescribe beta-blocker therapy.Results. Although there were no clinically significant heart rhythm disorders found, the patient with suspected family type of idiopathic ventricular tachicardia underwent cardioverter-defibrillator setting up procedure. Molecular-genetic methods helped to prove the diagnosis of "long-QT-syndrome type 1" and the cascade family screening was started to choose a treatment strategy for asymptopathic mutation bearers. Conclusion. By the example of the clinical case described we showed a significance of DNA-diagnostics in the diagnosis clarification, treatment strategy choice and sufficient medical-genetic consulting for the disease mentioned.