We performed a targeted mutational analysis of NOTCH1 using genomic DNA from 48 unrelated subjects with concomitant bicuspid aortic valve and thoracic aortic aneurysm using denaturing high-performance liquid chromatography and DNA sequencing.
Bicuspid aortic valve (BAV) is the commonest congenital heart disease and a highly heritable trait; however, only the NOTCH1 gene has been linked to limited cases of BAV in humans.
All exons and splice junctions of NOTCH1 were sequenced in probands from 13 affected families presenting with bicuspid aortic valve with ascending aortic aneurysm in the absence of valve calcification.
In conclusion, our study demonstrates that subjects with BAV display a significant deregulation of TLR4 signaling pathway paralleled by a deregulation of Notch-1 pathway, as previously showed.
Two novel NOTCH1 mutations were identified in two Italian families with BAV, highlighting the role of a NOTCH1 signaling pathway in BAV and its aortic complications.
Mutations in the NOTCH1 gene are one of only a few genetic anomalies identified in BAV disease; however evidence for defective NOTCH signaling, and its involvement in the characteristic histological changes of VSMC apoptosis and differentiation in ascending aortae of BAV patients is lacking.
These findings are the first to our knowledge to demonstrate an SHF lineage-specific role for Notch1 in AscAA and suggest that genes linked to the development of BAV may also contribute to the associated aortopathy.
NOTCH1 gene mutations might potentially contribute to the development of thoracic aortic aneurysms by affecting SMC differentiation in some patients with bicuspid aortic valve.
Furthermore, several mouse models of BAV have been described defining the role of endothelial Notch1 in aortic valve morphogenesis, whereas others have implicated new genes.
Nine genes previously associated with BAV (NOTCH1, AXIN1, EGFR, ENG, GATA5, NKX2-5, NOS3, PDIA2, and TGFBR2) were sequenced in 48 patients with BAV using the Ion Torrent Personal Genome Machine.
In conclusion, we identified a novel SMAD6 variant causing a severely calcified BAV and TAA, which contributes to our understanding of the clinical and genetic background of SMAD6-related BAV.
Rare heterozygous variants in SMAD6 have been identified as a significant genetic contributor to bicuspid aortic valve-associated thoracic aortic aneurysm on one hand and non-syndromic midline craniosynostosis on the other.
Causative gene mutations (for example, NOTCH1, SMAD6) are known for ≤1% of nonsyndromic BAV cases with and without AscAA<sup>5-8</sup>, impeding mechanistic insight and development of therapeutic strategies.
Although only 14% of the TAA patients also presented BAV, all novel likely pathogenic SMAD6 variants (N = 7) were identified in BAV/TAA individuals, further establishing the role of SMAD6 variants to the aetiology of BAV/TAA and revealing limited contribution to TAA development in patients with a tricuspid aortic valve.