To more precisely characterize the neuronal enrichments, we analyzed the five traits with neuronal enrichment at FDR<5% using t-statistics computed by the PsychENCODE consortium20 on differential expression in glutamatergic (excitatory) vs. GABAergic (inhibitory) neurons (Online Methods). The results are displayed in Figure 4c and Table S8c; we used Bonferroni correction in this analysis, as we were testing only 5×2=10 hypotheses. For bipolar disorder, genes that are specifically expressed in GABAergic neurons exhibited heritability enrichment, while genes specific to glutamatergic neurons did not. This result supports the theory that pathology in GABAergic neurons can contribute causally to risk for bipolar disorder51,52. For BMI and schizophrenia, on the other hand, we found significant enrichment in glutamatergic neurons but not in GABAergic neurons.
