Maternal mosaicism in long QT syndrome due to a pathogenic variant in KCNH2

Abstract

Identifying parental gonosomal mosaicism is useful Introduction We present the case of a singleton pregnancy presenting in utero with periods of 2:1 heart block with persistent fetal bradycardia and suspected fetal ventricular tachycardia. Postnatal clinical genetic testing identified a pathogenic variant in KCNH2. When familial site-specific genetic testing for the pathogenic variant was performed, the patient’s mother was identified as having possible mosaicism for the familial KCNH2 pathogenic variant. A subsequent pregnancy was also confirmed to have this pathogenic variant with similar prenatal and postnatal course as the proband. Other cases of mosaicism have been previously presented in genes related to inherited arrhythmias, including in SCN5A, but, to date, mosaicism has not been reported in KCNH2. to refine recurrence risk, as well as to provide the most appropriate care in future pregnancy management. Case report This study was approved by the University of Utah Institutional Review Board (IRB_00057688). A G3P1 30-year-old woman was referred by her obstetrician to maternal fetal medicine (MFM) for supervision of a high-risk pregnancy at 33 weeks. There were concerns of fetal bradycardia, as well as possible umbilical cord varix. The obstetrician noted a fetal heart rate reportedly close to 60 beats per minute (bpm), and there was concern for fetal 2:1 atrioventricular (AV) block with an atrial rate around 111 bpm and ventricular rate close to 50 bpm. anti-Ro/SSA and anti-La/SSB antibodies were sent and were reported to be negative. One day later, at a visit to the Fetal Cardiology