Exploration of cell type–specific somatic mutations in schizophrenia and the impact of maternal immune activation on the somatic mutation profile in the brain

Aim Schizophrenia (SZ) is a severe psychiatric disorder caused by the interaction of genetic and environmental factors. Although somatic mutations that occur in the brain after fertilization may play an important role in the cause of SZ, their frequencies and patterns in the brains of patients and related animal models have not been well studied. This study aimed to find somatic mutations related to the pathophysiology of SZ. Methods We performed whole‐exome sequencing (WES) of neuronal and nonneuronal nuclei isolated from the postmortem prefrontal cortex of patients with SZ ( n = 10) and controls ( n = 10). After detecting somatic mutations, we explored the similarities and differences in shared common mutations between two cell types and cell type–specific mutations. We also performed WES of prefrontal cortex samples from an animal model of SZ based on maternal immune activation (MIA) and explored the possible impact of MIA on the patterns of somatic mutations. Results We did not find quantitative differences in somatic mutations but found higher variant allele fractions of neuron‐specific mutations in patients with SZ. In the mouse model, we found a larger variation in the number of somatic mutations in the offspring of MIA mice, with the occurrence of somatic mutations in neurodevelopment‐related genes. Conclusion Somatic mutations occurring at an earlier stage of brain cell differentiation toward neurons may be important for the cause of SZ. MIA may affect somatic mutation profiles in the brain.