Mitral valve phenotypes in SMAD3-related thoracic aortic disease: insights from the Montalcino Aortic Consortium

Abstract Background SMAD3 pathogenic variants (PV) predispose to heritable thoracic aortic aneurysms and dissections (HTAD). Mitral annular disjunction (MAD) associated with mitral valve prolapse (MVP) and mitral regurgitation (MR) was identified as a potential new marker of disease severity in Marfan syndrome. The prevalence and prognostic impact of these mitral phenotypes in other forms of HTAD are less known. Purpose We hypothesize that mitral abnormalities are increased in SMAD3-related HTAD and are associated with increased risk for valve and aortic complications. Methods The Montalcino Aortic Consortium (MAC) registry has enrolled participants with PV in 15 HTAD genes. Subjects >16 years old with complete imaging and clinical data were included in this study. MVP was defined according to current guidelines. MR was classified as mild, moderate, or severe. MAD was defined by a >3-millimeter gap between the posterior mitral valve leaflet hinge point and the inferolateral myocardium as confirmed by direct measurement of echocardiogram images. Frequencies of MVP, MR, and MAD were compared between MAC participants with SMAD3 PV and other HTAD PV. Associations between clinical and echo characteristics and the composite outcome of arrhythmia, aortic surgery, aortic dissection, or congestive heart failure was evaluated with multivariable logistic regression. Results In 671 MAC participants (129 with SMAD3 PV, 36 [IQR 19-51] years, 49% female), the prevalence of MVP was 15% and the prevalence of MR was 22%. Both MVP (31/129, 24%, vs. 67/542, 12%, OR 2.2 [1.4-3.6], P<0.001) and MR (40/129, 31%, vs. 108/542, 20%, OR 1.8 [1.2-2.8], P<0.006) were more common in participants with SMAD3 PV compared to other PV and were further enriched in cases with SMAD3 missense PV compared to loss of function PV (MR or MVP: 26/48, 54% vs. 7/30, 23%, OR 3.9 [1.4-10.8], P<0.007). Images were available from 238 MAC participants (67 with SMAD3 PV) to assess for MAD. MAD (29/67, 43%, vs. 28/171, 16%, OR 3.9 [2.1-7.3], P<0.0001), or the composite of MR, MVP, or MAD (42/67, 63%, vs. 69/171, 35%, OR 3.2 [1.8-5.7], P<0.0001) was more common with SMAD3 PV compared to other PV (Figure 1). Twelve participants with SMAD3 PV (18%) had prominent mitral phenotypes (>mild MR, >10 mm MAD, or MAD with MVP) but no significant aortic dilation (Z<3). When controlling for age and sex, MR or MVP, but not MAD, was independently associated with the composite outcome (OR 16 [2.4-110], Figure 2). Conclusion Mitral valve pathology, including MVP, MR, and MAD, is increased in individuals with SMAD3 PV compared to other HTAD PV. Prominent mitral phenotypes related to SMAD3 missense PV may identify a high-risk subgroup with adverse cardiovascular outcomes. Because congenital mitral disease may be the primary presenting feature of SMAD3 PV, genetic testing for HTAD should be considered for such patients, especially if they also have a family history of thoracic aortic disease.