Identification of a possible pathogenic link between congenital long QT syndrome and epilepsy.

BACKGROUND: Long QT syndrome (LQTS) typically presents with syncope, seizures, or sudden death. Patients with LQTS have been misdiagnosed with a seizure disorder or epilepsy and treated with antiepileptic drug (AED) medication. The gene, KCNH2, responsible for type 2 LQTS (LQT2), was cloned originally from the hippocampus and encodes a potassium channel active in hippocampal astrocytes. We sought to test the hypothesis that a "seizure phenotype" was ascribed more commonly to patients with LQT2.
METHODS: Charts were reviewed for 343 consecutive, unrelated patients (232 females, average age at diagnosis 27 +/- 18 years, QTc 471 +/- 57 msec) clinically evaluated and genetically tested for LQTS from 1998 to 2006 at two large LQTS referral centers. A positive seizure phenotype was defined as the presence of either a personal or family history of seizures or history of AED therapy.
RESULTS: A seizure phenotype was recorded in 98/343 (29%) probands. A seizure phenotype was more common in LQT2 (36/77, 47%) than LQT1 (16/72, 22%, p < 0.002) and LQT3 (7/28, 25%, p < 0.05, NS). LQT1 and LQT3 combined cohorts did not differ significantly from expected, background rates of a seizure phenotype. A personal history of seizures was more common in LQT2 (30/77, 39%) than all other subtypes of LQTS (11/106, 10%, p < 0.001).
CONCLUSIONS: A diagnostic consideration of epilepsy and treatment with antiepileptic drug medications was more common in patients with LQT2. Like noncardiac organ phenotypes observed in other LQTS-susceptibility genes such as KCNQ1/deafness and SCN5A/gastrointestinal symptoms, this novel LQT2-epilepsy association raises the possibility that LQT2-causing perturbations in the KCNH2-encoded potassium channel may confer susceptibility for recurrent seizure activity.