A Japanese Family with Long QT Syndrome: Distinct Genetic and Phenotypic Features in Children of Asymptomatic Parents with SCN5A and KCNQ1 Mutations

Abstract

Concomitant with advances in genetic diagnosis of congenital long QT syndrome (LQTS), results of genetic analysis in patients with LQTS are becoming increasingly important in clinical practice to design appropriate treatment strategies. The present study reports an LQTS family. The proband was a female patient who exhibited repetitive exercise-induced syncope since the age of six, and her QT interval in ECG was markedly prolonged (0.67 s using Bazett’s formula). Except for her maternal great-grandfather who died suddenly in his 30s, she had no family history of syncope or sudden death. She was diagnosed with LQTS and was treated with a β-blocker. However, the syncope recurred at the age of ten. We performed genetic analysis of the proband and identified the heterozygous compound mutations, KCNQ1 p.K358_Q359del and SCN5A p.A1330T. Her father and elder sister carried heterozygous SCN5A p.A1330T, and her mother and younger sister carried heterozygous KCNQ1 p.K358_Q359del. Although the proband had not exhibited syncope for over 8 months with a β-blocker and a Na channel blocker, we considered placement of an implantable cardioverter-defibrillator as secondary prevention because of the severe phenotype and the compound mutations. Her elder sister who had a normal QT interval was followed without medication. In contrast, we started β-blocker therapy as primary prevention in her younger sister because she exhibited a prolonged QT interval after exercise. Detailed consideration of the gene mutations and evaluation of the phenotype were both important in determining treatment strategies.