Rethinking schizophrenia: insights from genomics and implications for research.

Recent genomic research, considered in the wider context of knowledge from outside genomics, provides significant conceptual insights into the aetiology and pathogenesis of schizophrenia. The evidence indicates that genetic risk is expressed across the lifespan, from foetal development through to adulthood, and involves multiple neuronal types and brain regions. Schizophrenia appears to be primarily a neuronal disorder, with synaptic dysfunction playing a central role in pathogenesis both during development and in mature adult brain function, alongside earlier non-synaptic neurodevelopmental mechanisms. Importantly, non-familial genetic and environmental factors substantially influence neurodevelopmental impairment, and this is often reflected in cognitive performance falling below familial expectations. Cognitive deficits and structural brain abnormalities are weakly correlated with familial genetic risk and are better understood as markers of neurodevelopmental vulnerability rather than causal mediators. Genomic findings also position schizophrenia within a neurodevelopmental continuum, spanning childhood-onset disorders to adult-onset psychiatric conditions, and suggest heterogeneity within schizophrenia, with some cases exhibiting stronger neurodevelopmental involvement. These findings challenge notions that schizophrenia can be ascribed to, or understood by studying, dysfunction in particular neuronal types, brain regions or circuits, or to defects at a particular stage of neurodevelopment. While schizophrenia appears to be predominantly a neuronal disorder, pathophysiology appears to be manifest widely across time and space, and in different neuronal types across the adult and foetal brain. Moreover, despite schizophrenia's high heritability, there is mounting evidence that non-familial genetic and environmental factors play important roles in the neurodevelopmental processes that impact on schizophrenia risk. Finally, variation in the impact of the neurodevelopmental factors appears to be key to understanding some of the heterogeneity within schizophrenia and the relationship between schizophrenia and other conditions. These observations have profound implications for future research, particularly in clarifying pathogenic mechanisms and refining diagnostic frameworks.