Brugada syndrome (BrS) is a fatal arrhythmia that causes an estimated 4% of all sudden death in high-incidence areas.
SCN5A
encodes cardiac sodium channel Na
V
1.5 and causes 25 to 30% of BrS cases. Here, we report generation of a knock-in (KI) mouse model of BrS (
Scn5a
G1746R/+
). Heterozygous KI mice recapitulated some of the clinical features of BrS, including an ST segment abnormality (a prominent J wave) on electrocardiograms and development of spontaneous ventricular tachyarrhythmias (VTs), seizures, and sudden death. VTs were caused by shortened cardiac action potential duration and late phase 3 early afterdepolarizations associated with reduced sodium current density (
INa
) and increased
Kcnd3
and
Cacna1c
expression. We developed a gene therapy using adeno-associated virus serotype 9 (AAV9) vector-mediated
MOG1
delivery for up-regulation of MOG1, a chaperone that binds to Na
V
1.5 and traffics it to the cell surface. MOG1 was chosen for gene therapy because the large size of the
SCN5A
coding sequence (6048 base pairs) exceeds the packaging capacity of AAV vectors. AAV9-
MOG1
gene therapy increased cell surface expression of Na
V
1.5 and ventricular
INa
, reversed up-regulation of
Kcnd3
and
Cacna1c
expression, normalized cardiac action potential abnormalities, abolished J waves, and blocked VT in
Scn5a
G1746R/+
mice. Gene therapy also rescued the phenotypes of cardiac arrhythmias and contractile dysfunction in heterozygous humanized KI mice with
SCN5A
mutation p.D1275N. Using a small chaperone protein may have broad implications for targeting disease-causing genes exceeding the size capacity of AAV vectors.