Genetic variation in CACNA1C, a gene that encodes the pore-forming alpha-1 subunit of CaV1.2 L-type voltage-gated calcium channels (LTCCs), has been strongly and consistently linked to both schizophrenia and bipolar disorder, among other psychiatric disorders.1–3 While schizophrenia and bipolar disorder can present very differently in the clinic, both are associated with a psychosis phenotype,4 and several studies have indicated that there is a shared genetic architecture between the two disorders,5,6 including in CACNA1C.7 This evidence concerns the gene CACNA1C and bipolar disorder.