Familial Short QT Syndrome: Phenotypic Variability and Challenges in Risk Stratification

Background: Short QT syndrome (SQTS) is a rare inherited cardiac channelopathy associated with high risk of atrial and ventricular arrhythmias and sudden cardiac death (SCD). Data on its natural history, genotype-phenotype correlations, and risk stratification remain limited. We aimed to evaluate all families with a confirmed diagnosis of SQTS identified at our National Referral Center through a descriptive case series, thereby contributing additional real-world data on this rare condition. Methods: A retrospective review was conducted of all families evaluated for suspected SQTS between 2011 and 2025 at the Inherited Cardiac Diseases Unit. Diagnosis was based on 2022 ESC guidelines (QTc ≤320 ms or ≤360 ms plus supportive features), clinical evaluation, and genetic testing. Families meeting diagnostic criteria were included for detailed phenotypic and genotypic characterization and longitudinal follow-up. Results: Among all patients assessed, two families met the criteria for SQTS. One family with three phenotype-positive individuals was gene-elusive. This family had a history of SCD and the proband presented atrial fibrillation. The second family carried a pathogenic KCNJ2 variant (p.Asp172Asn). However, only the proband fulfilled ECG criteria for SQTS (phenotype-positive) and there was no family history of SCD. No patients were treated with pharmacological therapy for QT prolongation. All affected individuals showed stable QT intervals (none <320 ms) and there were no malignant arrhythmic events during follow-up. Conclusions: These two families illustrate the wide phenotypic spectrum of SQTS and underscore the difficulty of risk stratification in asymptomatic individuals. The rarity of the disease, variable penetrance, and absence of robust prospective data hinder evidence-based management. Systematic registry participation and longitudinal studies are essential to refine risk prediction and therapeutic strategies.