BD is a highly heritable disorder, with a risk ratio of 8–1019 for first-degree relatives and heritability of ~ 85% derived from twin studies.20,21 The genetics of BD is not well known but it is considered to be polygenic, sharing common polygenic variations with schizophrenia.22 Genome-wide association studies (GWAS) reveal several genetic variants, including CACNA1C, ODZ4, ANK3 and NCAN,23–25 and several associated single-nucleotide polymorphisms along with multiple gene factors.26,27 Owing to the complexity and heterogeneity of the genetics of BD, it is difficult to develop gene-targeted or phenotypic animal models,28,29 which has resulted in slow advances in our understanding of the disease, especially at the cellular level.
