[A novel KCNQ1 mutation in Chinese with congenital long QT syndrome].
OBJECTIVE
Congenital long QT syndrome (LQTS) is an inherited disorder of cardiac repolarization characterized by prolongation of QT interval and polymorphic ventricular tachycardia torsade de pointes (TdP) in the electrocardiogram (ECG). Clinical symptoms include recurrent syncope, seizure or even sudden death. It is caused by mutations of at least seven genes, six of them encoding ion channels that determine the duration of ventricular action potentials. One of these genes, KCNQ1, encodes an alpha-subunit of cardiac slowly activated delayed rectifier potassium channel. Patients carrying mutations of KCNQ1 are named as LQT1, which accounts for 42% of patients with LQTS. This study sought to analyze the clinical data of Chinese with LQTS and to screen for the mutations of KCNQ1.


METHODS
The universally accepted phenotypic criteria of LQTS was used for identification of probands. There were six families with LQTS. They were enrolled in this study. Clinical and ECG data of each family member were recorded. Genomic DNA was prepared from peripheral blood lymphocytes. Polymerase chain reaction-single strand conformation polymorphism analysis was used to screen for mutations throughout the whole coding region of KCNQ1 and DNA sequencing was performed to determine the exact mutation site.


RESULTS
There were totally 13 patients in the six LQTS families. Five were male and eight female. One suffered from sudden death, 10 had syncope and 2 were asymptomatic. Eleven of the 13 patients had ECG data. Their QT and QTc (mean +/- SD) were (0.460 +/- 0.058) s and (0.516 +/- 0.058) s, respectively. TdP was observed in 3 patients (27%) during the syncope attack. By PCR-SSCP analysis, two novel KCNQ1 deletion mutations 356-357 Delta QQ and 626-631 Delta GSGGPP were identified in 7 patients of 2 families. None of 50 normal individuals carried these mutations, indicating these two mutations were likely to cause the disease. In addition, P448R was found in one affected and some unaffected members in other two families and in 7 of 50 (14%) normal individuals, indicating that this might be a polymorphism. All the three mutations located in C-terminal domain of KCNQ1 protein.


CONCLUSIONS
Two novel deletion mutations and one novel polymorphism of KCNQ1 gene were identified among 6 Chinese families with LQTS.
Liang
Lu
L
Capital Institute of Pediatrics, Beijing 100020, China.
Du
Zhong-dong
ZD
Cai
Ling-ling
LL
Wu
Jian-xin
JX
Zheng
Tong
T
Qi
Tie-xiong
TX
D000293:Adolescent; D000328:Adult; D001483:Base Sequence; D002648:Child; D004247:DNA / Q000737:chemistry / Q000235:genetics; D004252:DNA Mutational Analysis; D004562:Electrocardiography; D005260:Female; D006801:Humans; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; D008133:Long QT Syndrome / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D009154:Mutation; D010375:Pedigree; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D018807:Polymorphism, Single-Stranded Conformational; D015221:Potassium Channels / Q000235:genetics*; D024642:Potassium Channels, Voltage-Gated
D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D004247:DNA