ALX1-related frontonasal dysplasia results from defective neural crest cell development and migration

A pedigree of subjects presented with frontonasal dysplasia (FND). Genome sequencing and analysis identified a p.L165F missense variant in the homeodomain of the transcription factorALX1which was imputed to be pathogenic. Induced pluripotent stem cells (iPSC) were derived from the subjects and differentiated to neural crest cells (NCC).NCCderived fromALX1(L165F/L165F)iPSCwere more sensitive to apoptosis, showed an elevated expression of several neural crest progenitor state markers, and exhibited impaired migration compared to wild-type controls.NCCmigration was evaluatedin vivousing lineage tracing in a zebrafish model, which revealed defective migration of the anteriorNCCstream that contributes to the median portion of the anterior neurocranium, phenocopying the clinical presentation. Analysis of humanNCCculture media revealed a change in the level of bone morphogenic proteins (BMP), with a low level ofBMP2 and a high level ofBMP9. SolubleBMP2 andBMP9 antagonist treatments were able to rescue the defective migration phenotype. Taken together, these results demonstrate a mechanistic requirement ofALX1inNCCdevelopment and migration.