Table 1.
Demographic and clinical features of the 3 study groups
| Characteristics | Bipolar I disorder twins | Non-BPI co-twins | Control twin subjects | Difference between groups |
| n = 21 | n = 19 | n = 34 | ||
| Age in years | ||||
| Mean (±SD) | 44.4 (7.5) | 45.1 (8.1) | 46.2 (5.4) | F2,71 = 0.52, P = 0.60 |
| Gender | ||||
| Female, n (%) | 10 (48) | 11 (58) | 17 (50) | χ2 == 0.47, P = 0.79 |
| Education (SCID category) | ||||
| Mean (±SD) | 11.1 (4.9) | 10.9 (4.1) | 11.2 (4.2) | F2,71 = 0.01, P = 0.95 |
| Zygosity | ||||
| MZ, n (%) | 4 (19) | 2 (10.5) | 8 (23.5) | χ2 == 1.34, P = 0.51 |
| Handedness | ||||
| Right, n (%) | 21 (100) | 18 (95) | 33 (97) | χ2 == 1.06, P = 0.59 |
| Lifetime alcohol | ||||
| Abuse/dependence, n (%) | 5 (23.8) | 2 (10.5) | 2 (5.9) | χ2 == 3.97, P = 0.14 |
| Current alcohol | ||||
| Abuse/dependence, n (%) | 1 (4.8) | 0 (0) | 1 (2.9) | χ2 == 0.87, P = 0.65 |
| Lifetime anxiety | ||||
| Disorder, n (%) | 7 (33) | 3 (15.8) | 2 (5.9) | χ2 == 7.20, P = 0.03 |
| Lithium (mg/day) | ||||
| Mean (±SD) | 927 (249.4) | 0 | 0 | — |
| Any psychotropic | ||||
| Medication, n (%) | 15 (71) | 0 | 0 | — |
| Length of use of medication in years | ||||
| Mean (±SD) | 13.1 (9.6) | 0 | 0 | — |
| TBV, cc3 (±SD) | 1298.2 (125.6) | 1307.5 (140.5) | 1244.9 (125.6) | F2,71 = 1.5, P = 0.23 |
| Gray matter volume, cc3 (±SD) | 722.2 (83.3) | 725.3 (74.3) | 694.1 (62.5) | F2,71 = 1.6, P = 0.22 |
| White matter volume, cc3 (±SD) | 446.5 (87.8) | 461.7 (62.9) | 450.3 (64.5) | F2,71 = 0.25, P = 0.78 |
| Ventricular volume, cc3 (±SD) | 22.5 (14.0) | 19.8 (9.2) | 16.2 (5.6) | F2,71 = 2.9, P = 0.06* |
*BP < CTL, P = 0.07; BP = CO-TWIN; CO-TWIN = CTL; TBV = Total Brain Volume.