Novel mutation in KCNJ2 gene causes long QT interval syndrome type 7 and learning disability: A case report

Long QT interval syndrome type 7 (LQT7) is a rare hereditary multisystem disorder characterized by a classic triad of ventricular arrhythmias with QT interval prolongation, periodic paralysis, and distinctive skeletal and facial features. The Kir2.1 protein is encoded by the KCNJ2 gene, which has been associated with LQT7.

We report an 8-year-old boy who presented with frequent premature ventricular contraction with QRS electrical alternans, QT interval prolongation, bidirectional ventricular tachycardia, and learning disability with poor school performance. Gene sequencing revealed a novel missense mutation in the KCNJ2 gene (c.224 C>A, p.Thr75Lys).

The patient was diagnosed as LQT7 and a learning disability.

During the follow-up period, the ventricular arrhythmias were difficult to treat with β-blocker. Due to the frequent premature ventricular contraction and bidirectional ventricular tachycardia, radiofrequency catheter ablation was tried but failed.

An implantable cardioverter-defibrillator was recommended due to the recurrent syncope, but the boy's legal guardian rejected the recommendation, opting to continue his treatment in another hospital.

Clinical management is mostly focused on reducing adverse cardiac events. As a first option, β-blockers are often chosen as treatments for LQT7 patients, but there is no clear evidence for their effectiveness in preventing fatal arrhythmias. If the drug treatment is not effective, radiofrequency catheter ablation can be considered. However, it may be difficult to target accurately the right spot, and the attempt of the radiofrequency catheter ablation failed. Therefore, after ineffective medical treatment, implantable cardioverter-defibrillator implantation could be an option for patients with life-threatening cardiac events.