An Unusual Genetic Variant of Long QT Syndrome with Late Presentation in the Sixth Decade.

This case report describes a 57-year-old woman with a history of transient loss of consciousness, initially treated as epilepsy, who presented with recurrent torsades de pointes requiring direct-current cardioversion. Her evaluation revealed a prolonged corrected QT (QTc) interval, and, after excluding acquired causes, she was managed with a dual-chamber implantable cardioverter-defibrillator, β-blocker and mexiletine therapy, and a base rate of 80 bpm. Genetic analysis identified a previously unreported, possibly pathogenic compound heterozygosity in the AKAP9 gene (c.9443C>T, p.Thr3148Met and c.10515_10520delAACCGG, p.Thr3506_Gly3507del). Upon diagnosis of congenital long QT syndrome, her antiepileptic drugs were discontinued. At 6-month follow-up, she remained free of arrhythmic events with noted improvement in her QTc interval, highlighting the critical importance of accurate diagnosis and genotype-guided therapy in such cases.