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Background: Individuals harbouring SMAD3 pathogenic variants are at risk for aneurysms/dissections throughout the arterial tree. Based on prior reports of sex differences in thoracic aortic aneurysm/dissection, we investigated the sexual dimorphism for vascular events in SMAD3- variant-harbouring patients., Methods: We analysed two large pedigrees comprising 84 individuals segregating pathogenic missense variants affecting the same p.Arg287 residue in SMAD3 . We excluded individuals<40 years without vascular involvement, as they were too young to be classified. Individuals were subcategorised according to sex, the presence or absence and localisation (aneurysm/dissection with or without involvement of the aortic root/ascending aorta) of vascular lesions. We complemented our familial patient cohort with 178 SMAD3 patients reported in the literature between 2011 and 2023., Results: In our two pedigrees, 11/30 (37%) variant-harbouring females had no vascular involvement, whereas none of the variant-harboring males (n=23) had no vascular involvement (p=0.001). While the two groups did not differ by age, males were at higher risk of vascular complications (p=0.037), there was no age difference between sexes. Of the 19 females with vascular involvement, six (32%) had vascular involvment sparing the aortic root/ascending aorta, whereas of the 23 males with vascular invovlement, only one (4%) had vascular involvement sparing the aortic root/ascending aorta (p=0.034). In the literature, we identified 116 male and 62 female additional patients. In the combined cohort of 220 patients, we demonstrated an over-representation of males (p<0.001) and non-penetrance in females for vascular pathology involving the aortic root/ascending aorta (p=0.028)., Conclusions: Non-penetrance is more common in women, and normal echocardiography in at-risk females is not as reassuring for risk of vasculopathy in other locations. The higher non-penetrance in women creates an ascertainment bias and results in an over-representation of male patients in the literature., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2025. No commercial re-use. See rights and permissions. Published by BMJ Group.)

Background: SMAD6 encodes an intracellular inhibitor of the bone morphogenetic protein (BMP) signalling pathway. Until now, rare heterozygous loss-of-function variants in SMAD6 were demonstrated to increase the risk of disparate clinical disorders including cardiovascular disease, craniosynostosis and radioulnar synostosis. Only two unrelated patients harbouring biallelic SMAD6 variants presenting a complex cardiovascular phenotype and facial dysmorphism have been described., Cases: Here, we present the first two patients with craniosynostosis harbouring homozygous SMAD6 variants. The male probands, both born to healthy consanguineous parents, were diagnosed with metopic synostosis and bilateral or unilateral radioulnar synostosis. Additionally, one proband had global developmental delay. Echocardiographic evaluation did not reveal cardiac or outflow tract abnormalities., Molecular Analyses: The novel missense (c.[584T>G];[584T>G], p.[(Val195Gly)];[(Val195Gly)]) and missense/splice-site variant (c.[817G>A];[817G>A], r.[(817g>a,817delins[a;817+2&#95;817+228])];[(817g>a,817delins[a;817+2&#95;817+228])], p.[(Glu273Lys,Glu273Serfs*72)];[(Glu273Lys,Glu273Serfs*72)]) both locate in the functional MH1 domain of the protein and have not been reported in gnomAD database. Functional analyses of the variants showed reduced inhibition of BMP signalling or abnormal splicing, respectively, consistent with a hypomorphic mechanism of action., Conclusion: Our data expand the spectrum of variants and phenotypic spectrum associated with homozygous variants of SMAD6 to include craniosynostosis., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY. Published by BMJ.)