Patient-informed CRISPR screen identifies FLNB as a congenital heart disease and ciliopathy gene.

Heterotaxy (HTX) is a congenital disorder characterized by abnormal left-right organ placement, often leading to severe congenital heart disease (CHD). Despite advances in sequencing, many CHD and HTX-associated genes remain functionally unvalidated, hindering effective clinical diagnosis and management. Here, we leveraged a high-throughput CRISPR-Cas9 screening approach in the Xenopus model to rapidly evaluate candidate genes identified from whole-exome sequencing of human CHD patients. Our screen identified Filamin B (FLNB), an actin-binding protein previously linked to skeletal disorders but not to ciliopathies or CHD. We identified 5 probands with CHD and HTX, 3 with recessive and 2 with damaging heterozygous variants in FLNB. Disrupting flnb in Xenopus reproduced key features of the human HTX phenotype, including defects in cardiac development and impaired motile cilia function. Rescue experiments confirmed the functional conservation of human FLNB, directly implicating actin cytoskeletal disruption in ciliogenesis and left-right patterning defects. Our results provide crucial evidence linking human FLNB dysfunction to ciliopathies and CHD and HTX.