Elucidation of the genetic causes of bicuspid aortic valve disease

AIMS

The present study aims to characterize the genetic risk architecture of bicuspid aortic valve (BAV) disease, the most common congenital heart defect.

METHODS AND RESULTS

We carried out a genome-wide association study (GWAS) including 2236 BAV patients and 11 604 controls. This led to the identification of a new risk locus for BAV on chromosome 3q29. The single nucleotide polymorphism rs2550262 was genome-wide significant BAV associated (P = 3.49 × 10-08) and was replicated in an independent case-control sample. The risk locus encodes a deleterious missense variant in MUC4 (p.Ala4821Ser), a gene that is involved in epithelial-to-mesenchymal transformation. Mechanistical studies in zebrafish revealed that loss of Muc4 led to a delay in cardiac valvular development suggesting that loss of MUC4 may also play a role in aortic valve malformation. The GWAS also confirmed previously reported BAV risk loci at PALMD (P = 3.97 × 10-16), GATA4 (P = 1.61 × 10-09), and TEX41 (P = 7.68 × 10-04). In addition, the genetic BAV architecture was examined beyond the single-marker level revealing that a substantial fraction of BAV heritability is polygenic and ∼20% of the observed heritability can be explained by our GWAS data. Furthermore, we used the largest human single-cell atlas for foetal gene expression and show that the transcriptome profile in endothelial cells is a major source contributing to BAV pathology.

CONCLUSION

Our study provides a deeper understanding of the genetic risk architecture of BAV formation on the single marker and polygenic level.

Even a low transmitral pressure gradient after transcatheter mitral valve repair leads to impaired dynamic performance and increased left atrial endsystolic volumes

Funding Acknowledgements

Type of funding sources: None.

INTRODUCTION

Transcatheter mitral valve repair (TMVR) was shown to be safe and improves outcome in patients with severe functional mitral regurgitation (MR). Mean transmitral pressure gradients (MVG) < 5.0 mmHg are generally tolerated after TMVR. However, the prognostic relevance of this arbitrary threshold remains unclear and dynamic changes during physical exercise are not well examined.

METHODS

From 2017 to 2019 48 patients with an indication for TMVR were prospectively enrolled in a single center study. The total physical capacity was measured by dynamic stress echocardiography on bicycle at baseline, before discharge and follow-up (FUP, mean (± SD) of 8.2 ± 1.4 months). Patients were classified into two groups: "MVG present" (MVG ≥ 2.5mmHg, measured by transesophageal echocardiography intraoperatively after TMVR) or "MVG absent". Between group differences were compared with a two-sided t-test. For association analysis the Pearson Product-Moment correlation coefficient was used.

RESULTS

48 with a mean (± SD) age of 72.8 ± 12.1 years were eligible for the analysis. There was no significant difference in baseline characteristics concerning the level of the EuroScore II or prevalence of atrial fibrillation, heart failure, cardiovascular risk factors, renal failure or cardiomyopathy and demographic characteristics as age and sex, respectively. Also, most of the standard morphological and functional echocardiographic parameters as well as modern speckle-tracking derived parameters were similar between the 2 groups. There was no difference in remaining mitral regurgitation regarding severity between the two groups (p = 1.00). While the left atrial end systolic volumes (LAESV) at baseline did not differ significantly between groups, patients with an increased MVG after clipping showed an increase in LAESV (plus 56.2 ± 33.6 ml), while the other group showed a decrease in mean value (minus 15.9 ± 42.1 ml; baseline vs FUP: p < 0.001).

Further performance in dynamic stress echocardiography was significantly better in patients without development of a gradient (increase in metabolic equivalent of task (METS) changes between FUP and baseline 1.05 vs 0.06, p = 0.014).

Most importantly, those patients who had a higher MVG after TMVR showed a significant increase in MVG already during stress-echo at baseline, compared to patients who didn´t develop a significant MVG after intervention (1.45 ± 1,08 mmHg vs. 0.67 ± 1,00 mmHg; p = 0.026).

CONCLUSION

After TMVR even a low MVG increase of > = 2.5mmHg is associated with impaired performance in dynamic stress echo and with enlargement of LAESV. Increase of MVG in stress echo at baseline may be suitable to identify patients at risk to develop pathological MVG.

Therefore, periprocedural caution to hemodynamic changes in MVG should always be given. Maybe a certain residual MR could be accepted before implanting an additional clip, knowing that already a MVG > 2,5 mmHg might have adverse effects.