Whole Genome Sequencing and Familial Segregation Analysis Reveals CELSR1 Risk Alleles in Familial Bicuspid Aortic Valve and Hypoplastic Left Heart Syndrome

Background: Bicuspid aortic valve (BAV) is a common congenital heart disease (CHD); however, a complex genetic architecture evident by incomplete penetrance, variable expression, and genetic heterogeneity has hampered BAV gene discovery. Whole genome sequencing (WGS) and segregation analysis enable deciphering of CHD etiologies. A shared genetic basis for familial BAV and hypoplastic left heart syndrome (HLHS) was postulated for gene discovery.

Methods: WGS was performed in six multiplex BAV families, an HLHS cohort of 197 probands and 546 relatives, and 813 controls. Data were filtered for rare, predicted-damaging variants that cosegregated with familial BAV and disrupted genes associated with CHD in humans and/or mice. Candidate genes were further prioritized by rare variant burden testing in HLHS cases versus controls. Modifier variants in HLHS proband-parent trios were sought to account for the severe developmental phenotype.

Results: In five BAV families, missense variants in six ontologically diverse genes for structural (SPTBN1, PAXIP1, FBLN1) and signaling (CELSR1, PLXND1, NOS3) proteins fulfilled filtering metrics (Table 1). CELSR1, encoding cadherin EGF LAG seven-pass G-type receptor, was identified as a candidate gene (Figure 1) in two families and was the only gene demonstrating rare variant enrichment in HLHS probands (P=0.003575). HLHS-associated CELSR1 variants included 16 missense, one splice site, and three non-coding variants predicted to disrupt canonical transcription factor binding sites, most of which were inherited from a parent without CHD. Filtering WGS data for rare, predicted-damaging variants inherited from the other parent revealed two cases of CELSR1 compound heterozygosity, one case of CELSR1-CELSR3 synergistic heterozygosity, and four cases of CELSR1-MYO15A digenic heterozygosity.

Conclusion: CELSR1 is a susceptibility gene for familial BAV and HLHS, further implicating planar cell polarity pathway perturbation in CHD. Enrichment of rare CELSR1 variants in HLHS cohort provides corroborative evidence, postulating that CELSR1 variant burden or a second variant in a modifier gene could account for the severe developmental phenotype of HLHS compared to BAV.