To address the question of the relative importance of brain cell types, as opposed to brain regions, we analyzed the same set of traits using a publicly available data set of specifically expressed genes identified from different brain cell types purified from mouse forebrain19 (Online Methods). The results of this analysis are displayed in Figure 4b and Table S8b. We identified neuronal enrichments at FDR<5% for five traits: bipolar disorder, schizophrenia, years of education, BMI, and neuroticism. The other cell types did not exhibit significant enrichment for any of the 12 brain-related traits. The enrichment of neurons for all three of the traits with enrichment in cerebellum in the brain-region analysis supports the hypothesis that analyses of brain regions may be confounded by cell-type composition.
