Partially dominant mutant channel defect corresponding with intermediate LQT2 phenotype.

Area of Science:

• Genetics
• Molecular Biology
• Cardiology

Background:

• Hereditary Long QT Syndrome (LQTS) is a cardiac disorder characterized by delayed ventricular repolarization.
• The KCNH2 (HERG) gene encodes the cardiac potassium channel crucial for I(Kr) current.
• A novel G816V HERG mutation was identified in a patient with sudden cardiac death.

Observation:

• The G816V HERG mutation results in reduced protein expression and a trafficking defect.
• Mutant channels show decreased cell surface localization but can interact with wild-type subunits.
• Reduced expression and impaired function were observed at physiological temperatures.

Findings:

• The G816V HERG channel exhibits a trafficking defect, impairing potassium current conduction.
• Partial rescue of function was achieved at reduced temperatures, but with altered kinetics.
• Hypokalemia may exacerbate the condition by promoting WT HERG degradation and haplo-insufficiency.

Implications:

• The G816V mutation causes a partially dominant-negative trafficking defect, explaining varied clinical severity.
• This defect compromises repolarization reserve, increasing arrhythmia risk.
• Understanding this mutation's mechanism is vital for diagnosing and managing LQTS and sudden cardiac death.