For example, the offspring and siblings of schizophrenia have significantly higher risk of developing BD, and vice versa [12]; single nucleotide polymorphisms (SNPs) in the major histocompatibility complex (MHC) region, 3p21.1 region, CACNA1C, and TRANK1 have shown genome-wide significant associations with both schizophrenia and BD [13, 14]. Here, CACNA1C is linked to Behcet disease.