TRANK1 and bipolar disorder: Beyond early brain development, our data also point to a synaptic function for FRMD4A. TRANK1 is a GWAS-associated locus for both schizophrenia (Schizophrenia Working Group of the Psychiatric Genomics, 2014) and bipolar disorder (Chen et al., 2013; Muhleisen et al., 2014), but its functional roles in neurons are obscure.