Developmental and cellular vulnerabilities underlie genetic architecture of schizophrenia.

Schizophrenia (SZ) is a highly heritable neuropsychiatric condition with complex polygenic architecture. Elucidating the cellular and developmental substrates vulnerable to the genetic risk is essential for understanding the underlying neurobiological mechanisms. Here, we integrated genome-wide association study (GWAS) and whole-exome sequencing (WES) data with a developmental multi-omics atlas of the human cortex (including 5 cortical regions), comprising about 3 million single-nucleus RNA sequencing (snRNA-Seq) and single-nucleus assay for transposase-accessible chromatin using sequencing (snATAC-Seq) profiles across 8 neurodevelopmental processes, to map cell-type-specific enrichment of SZ genetic risk. Our enrichment analyses revealed that both common and rare genetic liabilities converged on broad excitatory and inhibitory neuronal classes. Across different statistical frameworks, we identified genetic enrichment within intratelencephalic (IT) projection neurons and layer 6b excitatory neurons (Ex-L6b) networks across multiple cortical regions. Stage-resolved developmental mapping in the frontal cortex showed that genetic liabilities, particularly the rare variants, are predominantly concentrated within early developmental processes, namely neurogenesis and neuronal migration. Differential expression analysis in postmortem frontal cortex snRNA-Seq datasets cross-validated the cellular substrates of the genetic liabilities. Collectively, our findings establish a high-resolution cellular and temporal framework of SZ susceptibility, implicating mature associative IT microcircuits, deep-layer thalamocortical-regulating networks, and early developmental specification windows as primary points of genetic convergence in SZ.