Confirmation of the role of pathogenic SMAD6 variants in bicuspid aortic valve-related aortopathy

• DOI: 10.1038/s41431-019-0363-z
• Publication Date: 2019-02-22T12:04:15Z
• Authors: Ilse Luyckx; Gretchen MacCarrick; Marlies Kempers; Josephina Meester; Céline Geryl; Olivier Rombouts; Nils Peeters; Charlotte Claes; Nele Boeckx; Natzi Sakalihasan; Adeline Jacquinet; Alexander Hoischen; Geert Vandeweyer; Sarah Van Lent; Johan Saenen; Emeline Van Craen...; Janneke Timmermans; Anthonie Duijnhouwer; Harry Dietz; Lut Van Laer; Bart Loeys; Aline Verstraeten
• Keywords: Penetrance; Etiology; Thoracic aortic aneurysm

Progressive dilatation of the thoracic aorta leads to thoracic aortic aneurysm (TAA), which is often asymptomatic but predisposes to lethal aortic dissections and ruptures. TAA is a common complication in patients with bicuspid aortic valve (BAV). Recently, rare loss-of-function SMAD6 variants were shown to contribute significantly to the genetic aetiology of BAV/TAA. Intriguingly, patients with craniosynostosis have also been reported to be explained molecularly by similar loss-of-function SMAD6 variants. While significantly reduced penetrance of craniosynostosis has been reported for the SMAD6 variants as such, near-complete penetrance is reached upon co-occurrence with a common BMP2 SNP risk allele. Here, we report on the results of a SMAD6-variant analysis in 473 unrelated non-syndromic TAA patients, of which the SMAD6-positive individuals were also studied for the presence of the BMP2 risk allele. 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. Familial segregation studies confirmed reduced penetrance (82%) and variable clinical expressivity, with coarctation of the aorta being a common comorbidity. None of our six BMP2+/SMAD6+ patients presented with craniosynostosis. Hence, the proposed digenic model for craniosynostosis was not supported in the presented BAV/TAA cohort, suggesting that additional factors are at play. Finally, our data provide improved insights into the clinical spectrum of SMAD6-related BAV/TAA and has important implications for molecular diagnostics.