Array Comparative Genomic Hybridization Identifies a Heterozygous Deletion of the Entire KCNJ2 Gene as a Cause of Sudden Cardiac Death

Abstract

Background—Large gene re-arrangements, not detectable by standard molecular genetic sequencing techniques, are present in a minority of patients with long QT syndrome (LQTS). We aimed to screen for large rearrangements in genes responsible for LQTS as part of the molecular autopsy of a 36 year old woman who died suddenly and had a negative autopsy. A retrospective analysis of an ECG identified a long QT interval, but sequencing of known LQT genes was uninformative.

Methods and Results—Array comparative genomic hybridization (aCGH) was used to screen for deletions and duplications in 101 genes implicated in cardiac disorders and sudden death using a post-mortem blood sample. A 542kb deletion encompassing the entire KCNJ2 gene was identified in the decedent. The mother had electrocardiographic U wave changes consistent with Andersen-Tawil Syndrome (ATS) and exaggerated by exercise, but none of the characteristic non-cardiac features. Fluorescence in situ hybridization (FISH) confirmed the deletion in the decedent and established its presence in the mother.

Conclusions—A novel application of aCGH and FISH has identified that LQTS and sudden cardiac death may occur as a result of a deletion of an entire gene. The case also supports recent research suggesting that non cardiac features of ATS occur only with missense or minor gene rearrangements in KCNJ2 resulting in a dominant negative effect on Kir2.x channels.