Variations in the poly-histidine repeat motif of HOXA1 predispose individuals to bicuspid aortic valve

Abstract Bicuspid aortic valve (BAV) is the most common cardiovascular malformation (0.5–1.2% of the population) and is often associated with premature aortic valve stenosis or insufficiency, aortic aneurysm and other congenital cardiac heart defects. Although highly heritable, few causal mutations have been identified in BAV patients. Here, we report the association of novel variants in the transcription factor HOXA1 with BAV in humans. Targeted sequencing of HOXA1 in a cohort of 333 BAV patients identified rare indel variants in the homopolymeric histidine tract of HOXA1. In vitro analysis revealed that disruption of the histidine repeat motif causes a significant reduction in the half-life of the protein, and that these variants are associated with a defective transcriptional activity of the HOXA1 protein. Targeting the zebrafish hoxa1a ortholog in vivo resulted in aortic valve defects that could be rescued by expressing the wild-type human HOXA1. Furthermore, expression of HOXA1 Histidine variants in zebrafish also impacted aortic valve development indicating a dominant negative effect of these mutated proteins. Lastly, homozygous knockout mice for Hoxa1 develop a BAV phenotype, which is associated with a very small, rudimentary non-coronary leaflet. Genetic lineage analysis indicates that this defect is caused by a strong reduction of mesenchymal cells in the intercalated cushion due to a failure of neural crest cell migration toward the heart which is consistent with our transcriptomic analysis showing a down-regulation of premigratory and migratory neural crest markers in Hoxa1−/− compared with control embryos. Together, these findings indicate that variants causing HOXA1 dysfunction play a significant role in the genetic cause of BAV in humans.