Prime example of perseverance

Finally, after 20 years of work we were able to unravel the multigenic origin of congenital heart disease in an extended family.

Initially, the family was recruited in 1996 (!) and published in 1997 by Heri Schunkert and colleagues (link to PubMed).

In 1999, we performed linkage analysis with microsatellite markers and identified a locus on chromosome 1 (link to abstract at EHJ). 

However, extensive candidate gene sequencing by Sanger revealed no pathogenic variant within this linkage region.

Several years later we decided to perform whole-exome and whole-genome sequencing in this family to get an answer finally.

Exome-sequencing and traditional re-sequencing revealed that twelve of nineteen family members carry a familial mutation [NM_004329.2:c.1328G>A (p.R443H)] which encodes a predicted deleterious variant of BMPR1A. This variant co-segregates with the linkage region on chromosome 1 that associates with the emergence of severe CHDs including Ebstein’s anomaly, atrioventricular septal defect, and others. 

Unfortunately, we were not able to pinpoint a genetic variant on chromosome 1 that could explain the phenotypes.

However, we started with functional studies in zebrafish (actually our very first zebrafish project) and could show that the continuous overexpression of the zebrafish homologous mutation bmpr1aap.R438H within endocardium causes a reduced AV valve area, a downregulation of Wnt/ß-catenin signaling at the AV canal, and growth of additional tissue mass in adult zebrafish hearts.

These findings opens now the possibility of testing genetic interactions between BMPR1A and other candidate genes within the linkage region on chromosome 1 which may provide a first step towards unraveling more complex genetic patterns in cardiovascular disease etiology.

The project involved many people at different places, former Ph.D. and MD students. Overall, we had a very complimentary collaboration, starting with classical linkage analysis, old-fashion and next-generation sequencing, and state-of-the-art zebrafish work.

In Lübeck, my thanks go to Till, Benedikt, Ingrid, and Zouhair! 
My extraordinary thanks go to Salim and Melina and their team members. The project could not have been completed without their help. 
And, last but not least, we thank the family members who continuously stayed in contact and provided us with samples and clinical data.

We hope to get funding for a follow-up study to shed more light into the link between BMPR1A mutation on chromosome 10 and the linkage region on chromosome 1. Project ideas are currently discussed; this project is not at its end.

But for now, we are looking forward to Till´s MD thesis defense. Stay tuned!


PS: The pdf of this manuscript can be found here