[Genetic and clinical characteristics of single and compound types of patients with long QT syndrome type 3].

ABSTRACT

Objective: To explore the genetic background and clinical features of patients with long QT syndrome type 3 (LQT3). Methods: This retrospective cohort included patients diagnosed with LQT3 at the Department of Cardiology, Renmin Hospital of Wuhan University from January 1998 to December 2022. Patients were categorized into compound type group and single type group based on the presence of a single SCN5A mutation. The two groups were followed up and the differences in baseline characteristics, electrocardiograms, and clinical events between the two groups and probands were compared. Kaplan-Meier curves were used for survival analysis, and the log-rank test was employed to compare the event-free survival rates of first cardiac events between the groups and probands. Results: A total of 97 LQT3 patients were enrolled, including 59 probands. The age at diagnosis was (23.45±19.86) years, with 46 patients (47.4%) being male. Among them, 89 patients were classified as single type group, while 8 patients were classified as compound type group. Genetic testing identified 49 SCN5A mutations, with missense mutations being the majority (91.8%), primarily located in transmembrane regions (40.8%, n=20), interdomain linker regions (28.6%, n=14), and C-terminus (22.4%, n=11). The first cardiac event occurred in 44 patients (45.4%), with an onset age of (13.82±12.50) years. The main trigger was identified as rest or sleep (54.5%, n=24). Compared with patients in single type group, patients in compound type group were younger at diagnosis ((10.35±10.28) years vs. (24.63±20.13) years, P=0.040), had a significantly higher proportion of syncope (87.5% (7/8) vs. 33.7% (30/89), P=0.009), aborted cardiac arrest (62.5% (5/8) vs. 11.2% (10/89), P=0.001), and a lower incidence of event-free survival rates of first cardiac events (12.5% (1/8) vs.58.4% (52/89), log-rank P=0.001). The probands in compound type group had a significantly higher proportion of aborted cardiac arrest comparing to probands in single type group (62.5% (5/8) vs. 17.6% (9/51), P=0.020), while the difference in the incidence rate of event-free survival rates of first cardiac events between the probands in two groups was not statistically significant (12.5% (1/8) vs. 39.2% (20/51), log-rank P=0.08). Conclusion: Compound type LQT3 patients are not uncommon. Such patients are diagnosed at a younger age and exhibit more severe phenotypes, requiring close follow-up and proactive intervention strategies.