McMahon et al. (2000) sequenced the whole mtDNA genome in nine probands of bipolar disorder pedigrees, and reported that four polymorphisms are potentially associated with bipolar disorder. However, association of these polymorphisms were not statistically significant after the correction of multiple testing. We also searched for mtDNA polymorphisms associated with bipolar disorder and suggested that mtDNA 10398A might be a risk factor for bipolar disorder (Kato et al., 2001). This was one of four variants provisionally associated in the study by McMahon. We generated cybrids from 35 volunteers and analyzed their mitochondrial calcium levels. By analyzing the whole mtDNA sequence in these cybrids, we found that 10398A/G polymorphism is one of two variants altering mitochondrial calcium levels (Kazuno et al., 2006).