dual specificity tyrosine-(Y)-phosphorylation-regulated kinase 1 A is a high-confidence autism risk gene that encodes a conserved kinase. In addition to autism, individuals with putative loss-of-function variants in exhibit microcephaly, intellectual disability, developmental delay and/or congenital anomalies of the kidney and urinary tract. is also located within the critical region for Down syndrome; therefore, understanding the role of in brain development is crucial for understanding the pathobiology of multiple developmental disorders. To characterize the function of this gene, we used the diploid frog We discover that Dyrk1a is expressed in ciliated tissues, localizes to ciliary axonemes and basal bodies, and is required for ciliogenesis. We also demonstrate that Dyrk1a localizes to mitotic spindles and that its inhibition leads to decreased forebrain size, abnormal cell cycle progression and cell death during brain development. These findings provide hypotheses about potential mechanisms of pathobiology and underscore the utility of as a model system for understanding neurodevelopmental disorders.