Cardiac sodium channel mutation associated with epinephrine-induced QT prolongation and sinus node dysfunction

Area of Science:

• Cardiovascular Genetics
• Molecular Cardiology
• Electrophysiology

Background:

• Long-QT syndrome (LQTS) is a genetic arrhythmia linked to mutations in KCNQ1, KCNH2, and SCN5A genes.
• LQT1 events often occur during exercise, while LQT3 events are more common during rest.

Observation:

• A Japanese man presented with sinus node dysfunction and QT interval prolongation during exercise and epinephrine stress tests.
• Genetic screening identified a heterozygous missense mutation, V2016M, in the SCN5A gene.

Findings:

• The V2016M mutation in the SCN5A gene resulted in loss-of-function, decreasing peak sodium current.
• Mutant channels exhibited gain-of-function with increased late sodium currents and impaired inactivation, particularly after PKA activation.
• These electrophysiological changes were observed in a heterologous expression system.

Implications:

• The identified SCN5A mutation (V2016M) explains the patient's atypical LQT3 phenotype, including sinus node dysfunction and exercise-induced QT prolongation.
• Understanding the dual loss- and gain-of-function properties of this mutation is crucial for diagnosing and managing LQTS patients with similar presentations.
• This finding highlights the complex genotype-phenotype correlations in inherited cardiac arrhythmias.