Clinical characteristics of 30 Czech families with long QT syndrome and KCNQ1 and KCNH2 gene mutations: importance of exercise testing.
BACKGROUND
Classic symptoms of long QT syndrome (LQTS) include prolongation of QT interval on electrocardiograph, syncope, and cardiac arrest due to a distinctive form of polymorphic ventricular tachycardia, known as Torsade de Pointes. We assessed occurrence of LQTS signs in individuals from 30 Czech families with mutations in KCNQ1 and KCNH2 genes.


RESULTS
One hundred five individuals from 30 Czech families with LQTS were genotyped for KCNQ1 and KCNH2. The occurrence of typical LQTS signs (pathologic prolongation of QT interval; syncope; cardiac arrest; Torsade de Pointes) was clinically assessed by exercise test with QT interval analysis. Family history of sudden cardiac death was taken. Statistical analysis was performed to determine correlation of clinical results and mutation status. KCNQ1 gene mutations were found in 23 families, and KCNH2 gene mutations in eight families. Only 46 (70%) of the 66 mutation carriers had at least two of the typical LQTS signs. The others were minimally or asymptomatic. From 39 noncarrier individuals, only 1 fulfilled the clinical criteria of LQTS diagnosis, another 4 had an intermediate probability of diagnosis. The exercise test had 92% sensitivity and 93% specificity for LQTS diagnosis.


CONCLUSIONS
Incidence of classical signs of LQTS was not high in Czech carriers of KCNQ1 and KCNH2 mutations. Therefore, proper diagnosis relies on detection of symptoms at presentation. The exercise test may be beneficial owing to its high sensitivity and specificity for LQTS diagnosis.
Department of Internal Medicine and Cardiology, University Hospital and Faculty of Medicine of Masaryk University, Brno, Czech Republic.
Irena
I
Andrsova
Tomas
T
Novotny
Jitka
J
Kadlecova
Alexandra
A
Bittnerova
Pavel
P
Vit
Alena
A
Florianova
Martina
M
Sisakova
Renata
R
Gaillyova
Lenka
L
Manouskova
Jindrich
J
Spinar
D000328:Adult; D018153:Czech Republic / Q000453:epidemiology; D000072237:ERG1 Potassium Channel; D004562:Electrocardiography / Q000706:statistics & numerical data*; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics*; D005080:Exercise Test / Q000706:statistics & numerical data*; D005260:Female; D020022:Genetic Predisposition to Disease / Q000453:epidemiology / Q000235:genetics; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000453:epidemiology / Q000235:genetics*; D008297:Male; D009154:Mutation / Q000235:genetics; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D015995:Prevalence; D062085:RNA, Long Noncoding / Q000235:genetics*; D015203:Reproducibility of Results; D018570:Risk Assessment; D012680:Sensitivity and Specificity
D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; C449939:KCNQ1OT1 RNA; D062085:RNA, Long Noncoding