Co-existence of RBM20 and KCNQ1 gene mutations in a patient with long QT syndrome and dilated cardiomyopathy. “Which came first: Chicken or the egg?”

A 60-year-old female patient was taken to the emergency department with a history of syncope. ECG revealed polymorphic ventricular tachycardia which necessitated recurrent DC cardioversion. Post-reversion ECG showed sinus rhythm with prolonged corrected QTc. Bedside transthoracic echocardiogram revealed features suggestive of dilated cardiomyopathy (DCM) with severe left ventricular dysfunction. Next reversion to VT was managed with intravenous propranolol and DC cardioversion after which she remained in sinus rhythm. After the initiation of beta-blocker, she developed sinus bradycardia followed by complete heart block. The concern we had while managing this case was whether the DCM caused the VT {then why long QTc?} OR was the long QTc causing DCM {due to same gene mutation}. Genetic analysis revealed the simultaneous occurrence of KCNQ1 and RBM20 mutation. Regarding the treatment given to our patient, we continued beta-blocker, left bundle branch optimized implantable cardioverter defibrillator {LOT - Dx ICD} was done with atrial sensing, the right ventricular coil as the defibrillator, and left bundle branch area pacing. In our patient, any of the two mutations could explain the occurrence of both DCM and long QTc. However genetic analysis revealed the simultaneous presence of both RBM20 and KCNQ1 mutation. To the best of our knowledge, this is the first report in the medical literature on the co-existence of RBM20 and KCNQ1 mutation.