[Gene mutation analysis of a Chinese family of congenital long Q-T syndrome type three].
OBJECTIVE
The congenital long QT syndrome (LQTs) is a hereditary disorder in which most affected family members have delayed ventricular repolarization manifested on the electrocardiogram (ECG) as QT interval prolongation. The disorder is associated with an increased propensity to arrhythmogenic syncope, polymorphous ventricular tachycardia (torsade de pointes), and sudden arrhythmic death. LQTs is due to mutations involving principally the myocyte ion-channels, and this monogenetic disorder has an autosomal inheritance pattern. This study investigated the gene mutation of a Chinese family of LQTs with multiple phenotypes including dilated cardiomyopathy (DCM) and cardiac conduction defects, thus to understand the molecular pathogenesis of the diseases.


METHODS
A three-generation Chinese LQTs family with multiple phenotypes was investigated. Blood sample was collected from the 8 family members and 100 unassociated normal individuals. Polymerase chain reaction (PCR)-DNA direct sequencing was performed to screen all exons and their flanking introns of SCN5A gene for mutation analysis. Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) was used to exclude polymorphism.


RESULTS
PCR amplification and subsequent direct sequencing of SCN5A from proband revealed a heterozygous deletion of nine base pairs (CAGAAGCCC) in exon 26, corresponding to the three amino acid residues Gln1507-Lys1508-Pro1509 (QKP). This mutation is localized in the linker region between DIII-DIV of SCN5A. The same mutation was found in another patient (her grandmother) and excluded in the remaining living subjects in this family. This mutation was confirmed using SSCP in 100 unassociated healthy individuals. Similar analysis excluded possible mutations that would lead to amino acid changes in KCNQ1, KCNH2 and LAMIN A/C commonly associated with LQTs and DCM with conduction disorders, no new mutations that would lead to amino acid changes was found.


CONCLUSIONS
The result of the present study suggests that SCN5A mutation delQKP1507-1509 exists in patients with LQTs. The delQKP1507-1509 of SCN5A is a novel mutation in Chinese people. The same mutation was previously reported in a French family with only a single LQTs phenotype. Further studies on functional expression of SCN5A mutation delQKP1507-1509 will be helpful to understand the mechanism of the multiple phenotypes.
Shi
Rui-ming
RM
Department of Pediatrics, First Affiliated Hospital, Cardiovascular Ion Channel Disease Laboratory of Medical College of Xi'an Jiaotong University, Xi'an 710061, China.
Ma
Ai-qun
AQ
Zhang
Yan-min
YM
Yang
Chun
C
Huang
Chen
C
Zhou
Xi-hui
XH
Liu
Xiao-hong
XH
D000293:Adolescent; D000328:Adult; D044466:Asian People / Q000235:genetics; D004252:DNA Mutational Analysis; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics; D005260:Female; D006801:Humans; D051657:KCNQ1 Potassium Channel / Q000235:genetics; D008133:Long QT Syndrome / Q000145:classification / Q000151:congenital / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D009154:Mutation; D062554:NAV1.5 Voltage-Gated Sodium Channel; D010375:Pedigree; D010641:Phenotype; D015222:Sodium Channels / Q000235:genetics
D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D051657:KCNQ1 Potassium Channel; D062554:NAV1.5 Voltage-Gated Sodium Channel; C568320:SCN5A protein, human; D015222:Sodium Channels