Two novel variants in the SLC4A3 gene in two families with Short QT Syndrome: the role of cascade screening

Abstract

Abstract Background Short QT syndrome (SQTS) is a rare, autosomal dominant disease causing sudden cardiac death (SCD). Genetic testing is recommended according to current guidelines. Variants in KCNQ1, KCNH2, KCNJ2 and SLC4A3 genes have been reported in SQTS. Purpose We report implications of genetic testing and cascade screening (CS) in two families with phenotypical presentation of SQTS and novel genetic variants of unknown significance. Methods We performed a thorough clinical and electrophysiological work-up of the index patients of both families. In addition, genetic screening was conducted. Subsequently, segregation analysis of potentially pathogenic variants was carried out in available relatives. Results Index patient 1 presented with a history of recurrent syncope. His ECG showed a shortened QTc of 340ms. Family history was unremarkable. Structural heart disease was excluded by cardiac MRI and coronary angiography. Genetic testing detected a rare heterozygous missense variant in the KCNH2 gene (p.(Arg328Cys), frequency 0.053%), predicted to be pathogenic according to various prediction algorithms (Polyphen, SIFT, Align GVGD, mutation taster). CS of relatives did not confirm this variant as the causative mutation. Reanalysis of whole-exome sequencing data revealed a novel heterozygous missense variant, p.(Arg370Cys) in the recently identified SLC4A3 gene. A variant at the same position has previously been associated with SQTS. CS suggested disease association. The second index patient had a SCD at the age of 17. A previously registered ECG showed a shortened QTc of 340ms. Autopsy revealed no structural heart disease. Post-mortem genetic testing revealed variants in the LDB3, MYH7 and a novel heterozygous missense variant, p.(Ser1039Arg) also in the SLC4A3 gene. Family history was positive for SCD in three 2° relatives. The index patient's father had a positive phenotype with a QTc of 365ms. CS again suggested disease association of the variant in the SLC4A3 gene only. Conclusion Genetic testing revealed two novel variants in the SLC4A3 gene, which was recently implicated in the pathogenesis of the SQTS. Predictive bioinformatic algorithms to assess the pathogenicity of missense variants are of limited relevance, but genetic analysis of additional unaffected and affected family members may be instrumental to identify pathogenic DNA sequence variations. Family tree index patients 1 and 2 Funding Acknowledgement Type of funding source: None