Inherited arrhythmic disorders in Japan

Area of Science:

• Cardiology
• Genetics
• Molecular Biology

Background:

• Inherited arrhythmic disorders, including hereditary long QT syndrome (LQTS) and Brugada syndrome, pose significant health challenges.
• Understanding the genetic underpinnings and clinical characteristics of these conditions in diverse populations is crucial for diagnosis and treatment.
• Japan presents a unique demographic for studying these genetic heart conditions.

Purpose of the Study:

• To summarize the clinical and genetic characteristics of inherited arrhythmic disorders in Japan.
• To compare the genetic landscape of LQTS and Brugada syndrome in Japan with international findings.
• To investigate novel mutations and their functional consequences in Japanese patients.

Main Methods:

• Review of clinical and genetic data for inherited arrhythmic disorders in Japan.
• Analysis of mutation frequencies and types in LQTS (LQT1, LQT2, LQT3, LQT7) and Brugada syndrome.
• Functional assays of identified ion channel gene mutations (KCNJ2, KvLQT1, HERG, SCN5A) using heterologous expression systems.

Main Results:

• Hereditary long QT syndrome (LQTS) incidence in Japan is comparable to Western countries, primarily LQT1 and LQT2 genotypes, with predominantly novel mutations.
• Functional assays revealed novel mechanisms of ion channel dysfunction in LQTS.
• Brugada syndrome appears prevalent in Japan, but SCN5A mutations are found in only ~12% of cases, indicating an unknown genetic basis for most.
• A novel SCN5A mutation causing idiopathic ventricular fibrillation with suppressed channel function was identified.

Conclusions:

• Japanese LQTS patients exhibit distinct novel mutations, necessitating tailored genetic diagnostics.
• The genetic etiology of the majority of Brugada syndrome cases in Japan remains elusive.
• Further research into genetic variations and their functional impact is essential for understanding and managing inherited arrhythmias.