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Two recent studies reported evidence for association between genetic variation of the positional candidate gene P2RX7 on chromosome 12q24 and bipolar I disorder (BPI) [Barden et al. (2006); Am J Med Genet Part B 141B:374-382; McQuillin et al. (2008); Mol Psychiatry 13:1-7] and one study found association with unipolar major depression (Mdd-UP) [Lucae et al. (2006); Hum Mol Genet 15:2438-2445]. In the present work, we aimed to replicate the SNP that showed the strongest association in the above-mentioned studies, namely rs2230912 (P2RX7-E13A) resulting in a change of the amino acid glutamine to arginine at position 460 (Gln460Arg), in four European bipolar I disorder samples from Germany, Poland, Romania, and Russia totaling 1,445 patients, in a German sample of recurrent Mdd-UP patients (N = 640), and a control sample of 2,006 subjects. We found no allelic or genotypic association between rs2230912 and BPI or Mdd-UP both in the national samples and in the combined European patient sample. Additional studies are needed to clarify the potential involvement of P2RX7 and of SNP rs2230912 in the etiology of major affective disorders.

Age of onset (AO) has been proposed as a promising criterion by which to select homogeneous subgroups for the genetic analysis of bipolar disorder. This is the first study to investigate the effect of the interaction between gender and family history (FH)-type on AO in bipolar disorder. In accordance with the literature, no difference in AO was observed between females and males in our sample of 264 Romanian bipolar I probands. Cox regression, however, showed a strong influence of FH-type on AO (P = 0.006). This was due to a significant variation in AO according to the type of FH in females (P = 0.002) but not in males (P = 0.64). Female bipolar disorder patients with a negative FH (FH(-)) had a later AO than females with either a FH of bipolar and/or schizoaffective disorder (P = 0.001) or a FH of recurrent unipolar major depression only (P = 0.04). Females with FH(-) had a later AO than males with FH(-) (P = 0.03). No sex difference was observed for AO in the group with a FH of recurrent unipolar depression. In the group with a FH of bipolar and/or schizoaffective disorder, females had an earlier AO than males (P = 0.01). A trend for support was observed in an independent sample of 217 German bipolar I patients for an influence of FH-type on AO in females (P = 0.09) but not in males (P = 0.15). Female bipolar disorder patients with FH(-) had a later AO than females with either a FH of bipolar and/or schizoaffective disorder (P = 0.04) or a FH of recurrent unipolar major depression only (P = 0.05). Females with FH(-) had a later AO than males with FH(-) (P = 0.05). Other comparisons were statistically not significant, which may be due to limited sample size. Our findings emphasize that the interaction between gender and FH-type is a source of heterogeneity for AO in bipolar disorder.