ISL1 loss-of-function variation causes familial atrial fibrillation

Atrial fibrillation (AF) represents the most frequent form of sustained cardiac rhythm disturbance, affecting approximately 1% of the general population worldwide, and confers a substantially enhanced risk of cerebral stroke, heart failure, and death. Increasing epidemiological studies have clearly demonstrated a strong genetic basis for AF, and variants in a wide range of genes, including those coding for ion channels, gap junction channels, cardiac structural proteins and transcription factors, have been identified to underlie AF. Nevertheless, the genetic pathogenesis of AF is complex and still far from completely understood. Here, whole-exome sequencing and bioinformatics analyses of a three-generation family with AF were performed, and after filtering variants by multiple metrics, we identified a heterozygous variant in the ISL1 gene (encoding a transcription factor critical for embryonic cardiogenesis and postnatal cardiac remodeling), NM_002202.2: c.481G > T; p.(Glu161*), which was validated by Sanger sequencing and segregated with autosome-dominant AF in the family with complete penetrance. The nonsense variant was absent from 284 unrelated healthy individuals used as controls. Functional assays with a dual-luciferase reporter assay system revealed that the truncating ISL1 protein lost transcriptional activation on the verified target genes MEF2C and NKX2-5. Additionally, the variant nullified the synergistic transactivation between ISL1 and TBX5 as well as GATA4, two other transcription factors that have been implicated in AF. The findings suggest ISL1 as a novel gene contributing to AF, which adds new insight to the genetic mechanisms underpinning AF, implying potential implications for genetic testing and risk stratification of the AF family members.