Disruptions during the development of the brain are thought to play a critical role in the onset of a range of brain disorders. Whilst many studies have evaluated how cell-type specific gene expression is associated with risk for psychiatric disorders, the potentially critical role of developmental dynamics of gene expression has not yet been investigated. Here, we leverage a recently published snRNA-seq dataset from 27 human prefrontal cortex samples, spanning foetal to adult stages, and explore disease associations of developmentally-regulated genes. To this end, we applied the MAGMA algorithm to perform gene set enrichment analysis based on genome-wide association studies for 11 brain-related traits. We find that genes developmentally regulated in excitatory and inhibitory neurons are strongly enriched for variants associated with schizophrenia, and to a lesser extent intelligence and bipolar disorder. Further, although microglial-specific genes are associated with Alzheimer’s disease, consistent with previous observations, we find no evidence of association for developmentally-regulated genes. Our results represent a step forward in mapping disease risk to cell types, by providing insights into the role of developmental regulation of gene expression at cell-type resolution.