A possible association between the -116C/G single nucleotide polymorphism of the XBP1 gene and lithium prophylaxis in bipolar disorder.

Bipolar disorder (BPD) is a severe, chronic, and life-threatening illness, and its pathogenesis remains unclear. Recently, a functional polymorphism (-116C/G) of the X-box binding protein 1 (XBP1) gene was reported to be a genetic risk factor for BPD. Moreover, the endoplasmic reticulum stress responses were impaired in cultured lymphocytes from BPD patients with the -116G allele and only valproate rescued such impairment among three major mood stabilizers. In this context, we hypothesized that BPD patients with different genotypes respond differently to mood stabilizers. We investigated the association between the -116C/G polymorphism of the XBP1 gene and lithium response in Japanese patients with BPD. We found that lithium treatment is more effective among BPD patients with the -116C allele carrier than in patients homozygous for the -116G allele. The association between the -116C/G polymorphism and clinical efficacy of mood stabilizers should be further investigated in a prospective study with a larger sample.