Biallelic DAW1 variants cause a motile ciliopathy characterized by laterality defects and subtle ciliary beating abnormalities.

PURPOSE: The clinical spectrum of motile ciliopathies includes laterality defects, hydrocephalus, and infertility as well as primary ciliary dyskinesia when impaired mucociliary clearance results in otosinopulmonary disease. Importantly, approximately 30% of patients with primary ciliary dyskinesia lack a genetic diagnosis. METHODS: Clinical, genomic, biochemical, and functional studies were performed alongside in vivo modeling of DAW1 variants. RESULTS: In this study, we identified biallelic DAW1 variants associated with laterality defects and respiratory symptoms compatible with motile cilia dysfunction. In early mouse embryos, we showed that Daw1 expression is limited to distal, motile ciliated cells of the node, consistent with a role in left-right patterning. daw1 mutant zebrafish exhibited reduced cilia motility and left-right patterning defects, including cardiac looping abnormalities. Importantly, these defects were rescued by wild-type, but not mutant daw1, gene expression. In addition, pathogenic DAW1 missense variants displayed reduced protein stability, whereas DAW1 loss-of-function was associated with distal type 2 outer dynein arm assembly defects involving axonemal respiratory cilia proteins, explaining the reduced cilia-induced fluid flow in particle tracking velocimetry experiments. CONCLUSION: Our data define biallelic DAW1 variants as a cause of human motile ciliopathy and determine that the disease mechanism involves motile cilia dysfunction, explaining the ciliary beating defects observed in affected individuals.

Daw1 regulates the timely onset of cilia motility during development.

Motile cilia generate cell propulsion and extracellular fluid flows that are crucial for airway clearance, fertility and left-right patterning. Motility is powered by dynein arm complexes that are assembled in the cytoplasm then imported into the cilium. Studies in Chlamydomonas reinhardtii showed that ODA16 is a cofactor which promotes dynein arm import. Here, we demonstrate that the zebrafish homolog of ODA16, Daw1, facilitates the onset of robust cilia motility during development. Without Daw1, cilia showed markedly reduced motility during early development; however, motility subsequently increased to attain close to wild-type levels. Delayed motility onset led to differential effects on early and late cilia-dependent processes. Remarkably, abnormal body axis curves, which formed during the first day of development due to reduced cilia motility, self-corrected when motility later reached wild-type levels. Zebrafish larva therefore possess the ability to survey and correct body shape abnormalities. This work defines Daw1 as a factor which promotes the onset of timely cilia motility and can explain why human patients harboring DAW1 mutations exhibit significant laterality perturbations but mild airway and fertility complications.