Molecular and clinical characterization of a novel SCN5A mutation associated with atrioventricular block and dilated cardiomyopathy.
BACKGROUND
Increased susceptibility to dilated cardiomyopathy has been observed in patients carrying mutations in the SCN5A gene, but the underlying mechanism remains unclear. In this study, we identified and characterized, both in vitro and clinically, an SCN5A mutation associated with familial progressive atrioventricular block of adult onset and dilated cardiomyopathy in a Chinese family.


RESULTS
Among 32 family members, 5 were initially diagnosed with atrioventricular block after age 30; 4 were studied, 3 of whom later developed dilated cardiomyopathy. We found a heterozygous single-nucleotide mutation resulting in an amino acid substitution (A1180V) in all studied patients and in 6 other younger unaffected members but not in 200 control chromosomes. When expressed with the beta1 subunit, the mutated channels exhibited a -4.5-mV shift of inactivation with slower recovery leading to a rate-dependent Na(+) current reduction and a moderate increase in late Na(+) current. Clinical study revealed that although QRS duration decreased with increasing heart rate in noncarrier family members, this change was blunted in unaffected carriers whose ECG and heart function were normal. Resting corrected QT interval of unaffected carriers was significantly longer than that of noncarriers, even though it was still within the normal range.


CONCLUSIONS
A1180V expresses a mild Na(+) channel phenotype in vitro and a corresponding clinical phenotype in unaffected mutation carriers, implying that A1180V caused structural heart disease in affected carriers by disturbing Na(+) influx and, hence, cellular Na(+) homeostasis. The high penetrance of A1180V suggests this phenotype as a high risk factor for dilated cardiomyopathy with preceding atrioventricular block.
Ge
Junbo
J
Shanghai Institute of Cardiovascular Diseases, Zhongshan Hospital, Fudan University, Shanghai, China. gejunbo@zshospital.net
Sun
Aijun
A
Paajanen
Vesa
V
Wang
Shijun
S
Su
Chunxi
C
Yang
Zhiyin
Z
Li
Ying
Y
Wang
Shaochun
S
Jia
Jianguo
J
Wang
Keqiang
K
Zou
Yunzeng
Y
Gao
Lizhi
L
Wang
Kun
K
Fan
Zheng
Z
D000328:Adult; D000409:Alanine; D019943:Amino Acid Substitution; D044466:Asian People / Q000235:genetics; D054537:Atrioventricular Block / Q000208:ethnology / Q000235:genetics* / Q000503:physiopathology; D001483:Base Sequence; D002311:Cardiomyopathy, Dilated / Q000208:ethnology / Q000235:genetics* / Q000503:physiopathology; D002460:Cell Line; D018450:Disease Progression; D004562:Electrocardiography; D004594:Electrophysiology; D005080:Exercise Test; D005260:Female; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000235:genetics*; D062554:NAV1.5 Voltage-Gated Sodium Channel; D010375:Pedigree; D020641:Polymorphism, Single Nucleotide; D015222:Sodium Channels / Q000235:genetics*; D014633:Valine; D055815:Young Adult
D009124:Muscle Proteins; D062554:NAV1.5 Voltage-Gated Sodium Channel; C568320:SCN5A protein, human; D015222:Sodium Channels; D014633:Valine; D000409:Alanine