We also identified several non-psychiatric phenotypes with enrichments in brain cell types. For both BMI and age at menarche, cell types in the central nervous system (CNS) ranked highest among individual cell types, and the top cell-type group was CNS, all with FDR < 0.05. These enrichments support previous human and animal studies that propose a strong neural basis for the regulation of energy homeostasis [44]. For educational attainment, the top cell-type group is CNS (FDR < 0.05) and of the ten cell types that are significant after multiple testing, nine are CNS cell types. This is consistent with our understanding that the genetic component of educational attainment, which excludes environmental factors and population structure, is highly correlated with IQ [45]. Finally, for smoking behavior, the CNS cell-type group is significant and the top cell type is again a brain cell type, likely reflecting CNS involvement in nicotine processing.
