Within fetal frontal cortex NeuN– nuclei, we observed enrichment of SNP heritability for schizophrenia (8.14-fold enrichment, Z-score p = 1.2 × 10−7) and ADHD (8.69-fold enrichment, Z-score p = 1.54 × 10−4) at Z-score p-values surviving Bonferroni correction, and for bipolar disorder at nominal significance (5.82-fold enrichment, Z-score p = .01). Here, RBFOX3 is linked to bipolar disorder.