Novel characteristics of a misprocessed mutant HERG channel linked to hereditary long QT syndrome

Area of Science:

• Cardiovascular Genetics
• Molecular Cardiology
• Ion Channel Physiology

Background:

• Hereditary long QT syndrome (hLQTS) is a genetic disorder causing arrhythmias and sudden death.
• Mutations in the HERG (KCNH2) gene are a common cause of hLQTS, typically reducing potassium channel function.
• Understanding mutation mechanisms is crucial for developing targeted therapies.

Purpose of the Study:

• Investigate the functional and trafficking properties of a novel HERG COOH-terminal missense mutation, R752W.
• Determine the molecular basis for hLQTS in a family with this mutation.
• Classify the mutation to inform potential therapeutic strategies.

Main Methods:

• Genetic analysis of a family with hLQTS to identify the R752W mutation.
• Expression of wild-type and mutant HERG cRNA in Xenopus oocytes.
• Electrophysiological recordings to measure potassium currents.
• Mammalian cell culture to assess protein trafficking and localization.
• Computer simulations using the Luo-Rudy model.

Main Results:

• The HERG R752W mutation segregated with hLQTS in the studied family.
• Expressed mutant channels showed enhanced currents in oocytes, contrary to expectations.
• Simulations predicted normal or shortened cardiac action potentials.
• The mutant protein exhibited intracellular retention, indicating a trafficking defect in mammalian cells.
• Lower incubation temperatures rescued channel trafficking to the plasma membrane, restoring function.

Conclusions:

• HERG R752W represents a novel class of trafficking-deficient mutants in hLQTS.
• This mutation causes hLQTS through impaired protein transport, not altered channel gating.
• The diverse mechanisms of HERG channel dysfunction necessitate tailored therapeutic approaches for hLQTS.
• Future treatments must consider the specific class of trafficking defect for optimal efficacy.