Twin and family studies have shown that bipolar disorder tends to run in families with an estimated genetic hereditary of 63% [22]. Interestingly, besides the shared clinical symptoms, bipolar disorder and schizophrenia may also share a genetic background [23]. A number of promising susceptibility genes for schizophrenia have been reported to associate with bipolar disorder as well, including G72, DAO, DISC1, NRG1, RGS4, COMT, neural cell adhesion molecule 1 (NCAM1; 11q23.1), brain-derived neurotrophic factor (BDNF; 11p13) glutamate receptor, metabotropic 3 and 4 (GRM3; 7q21.1-q21.2 and GRM4; 6p21.3), glutamate receptor, ionotropic, N-methyl D-aspartate 2B (GRIN2B; 12p12), megalencephalic leukoencephalopathy with subcortical cysts 1 (MLC1; 22q13.33), synaptogyrin 1 (SYNGR1; 22q13.1) and solute carrier family 12 (potassium/chloride transporters), member 6 (SLC12A6; 15q13-q15) [reviewed in reviewed in 21, 24]. Recently, The Wellcome Trust Case Control Consortium reported a GWA study on bipolar disorder using the Affymetrix GeneChip 500K Mapping Array Set and found one chromosomal region with strong evidence of association (16p12) and 13 regions with moderate association (2p25, 2q12, 2q14, 2q37, 3p23, 3q27, 6p21, 8p12, 9q32, 14q22, 14q32, 16q12 and 20p13) [25]. (For a complete list of the genetic associations with bipolar disorder, we refer to http://www.polygenicpathways.co.uk/Bipolargenes.html).
