MSc BY RESEARCH: ABCC9 mutations and risk of sudden cardiac death

Sudden cardiac death (SCD) is an important clinical problem and has a lasting impact on relatives of the deceased, particularly when sudden death occurs in infancy. Mutations to cardiac ion channels and transporter genes are known to give rise to heritable conditions that predispose towards sudden death (e.g [1,2]). However, in many cases screening candidate genes for mutations either does not reveal positive results or yields ‘variants of uncertain significance’ (VUS). Categorization of missense variants as VUS poses a particular problem as, without definitive functional analysis, a VUS cannot be used for clinical diagnosis.  Several different potassium channel genes have been implicated in heritable arrhythmias and SCD.  Cardiac K_ATP channels (formed from Kir6.x and SUR2 co-assembly) are considered to be important under conditions of metabolic stress, when intracellular ATP levels fall. The resulting K_ATP channel activation shortens ventricular action potentials and protects against Ca²⁺_i overload and arrhythmia. On the other hand, aberrant K_ATP activation may itself lead to increased arrhythmia risk. Recently, gain-of-function mutations to ABCC9, have been identified in infant sudden death; ABCC9 encodes the SUR2A subunit of the K_ATP channel [3]. A missense SUR2A mutation has also been implicated in an overlap arrhythmia syndrome characterized by abbreviated ventricular repolarisation [4]. This project focuses on the identified mutations (SUR2A-A355S; [3], SUR2A-R663C [4]) and a reported VUS (SUR2A-R661C; ClinVar 191589).

Aims and Objectives: The A355S mutation is known to increase K_ATP channel (Kir6.2+SUR2A) current [3]. Aim 1 is to determine whether or not channels incorporating the R661C and R663C SUR2A variants also exhibit an increase in K_ATP channel function. Aim 2 is to test the effects of the clinically used sulphonylurea glibenclamide, to determine if this drug can mitigate any gain-of-function effects. Findings from this project should lead to a better understanding of the role of SUR2A mutations as predisposing factors for arrhythmia and sudden death.

This project will use a variety of techniques that are already established in the Hancox and Harmer laboratories, including: Molecular biology: PCR, mutagenesis, cloning, plasmid purification etc. Cell culture and transient transfection: of heterologous cell lines). Ion channel function: Whole-cell patch-clamp electrophysiology and ion channel pharmacology.