Next, we plotted the developmental expression trajectories of brain disorder risk genes (Fig. 2b–c). ASD-, SCZ-, and MDD-associated genes showed remarkedly similar expression patterns with a peak at the developmental stage 5 (16–19 PCW). BD- and ADHD-associated genes were gradually increased during the prenatal stage with a peak at the developmental stage 6 (19–22 PCW). Developmental stages 5 and 6 represent mid-gestation, the period during which upper layer neurons are generated and neuronal differentiation including axonogenesis and dendritic arborization takes place12,13. This result highlights mid-gestation as a critical window during neurodevelopment that may confer risk to multiple psychiatric disorders, consistent with recent results from cross-disorder GWAS14,15. On the contrary, degenerative disorders showed distinct expression trajectories. Genes associated with degenerative disorders except MS constantly and gradually increased during both prenatal and postnatal stages, suggesting that these genes may become more susceptible upon aging. This result is consistent with a strong neurodevelopmental predisposition for psychiatric disorders, in contrast with degenerative disorders which have a postnatal origin.
