Demographic and clinical comparison of affected, high-risk and low-risk monozygotic twins (n = 129)
| Variable* | Affected twins (n = 62) | High-risk twins (n = 38) | Low-risk twins (n = 29) | F value | p value |
|---|---|---|---|---|---|
| Age, yr | 37.5 (35.2–39.8) | 36.6 (33.7–39.5) | 37.4 (34.1–40.8) | F2,125 = 0.12 | 0.89 |
| Education, yr | 14.8 (14.0–15.6) | 15.7 (14.7–16.7) | 15.5 (14.3–16.7) | F2,125 = 1.01 | 0.37 |
| Premorbid IQ† | 113.5 (111.9–115.1) | 112.0 (109.8–114.2) | 110.6 (105.6–115.6) | F2,116 = 1.05 | 0.35 |
| Female, n (%) | 43 (69) | 26 (68) | 21 (72) | F2 = 0.76 | 0.68 |
| Left-handed (LQ < 0), n (%) | 10 (16) | 9 (24) | < 5 | F2 = 3.7 | 0.16 |
| Bipolar I disorder, n (%) | 19 (31) | NA | NA | — | — |
| Bipolar II disorder, n (%) | 5 (8) | NA | NA | — | — |
| Unipolar disorder, n (%) | 38 (61) | NA | NA | — | — |
| No. of episodes | 4.3 (3.3–5.4) | NA | NA | — | — |
| Age at onset, yr | 24.2 (22.4–26.0) | NA | NA | — | — |
| Medications, n (%) | |||||
| Antidepressant | 25 (40) | < 5 | 0 | — | — |
| Lithium | 12 (19) | 0 | 0 | — | — |
| Anticonvulsant | 12 (19) | 0 | 0 | — | — |
| Antipsychotic | 12 (19) | 0 | 0 | — | — |
| Comorbid disorders, n (%) | |||||
| Anxiety disorder | 5 (8) | 5 (13) | < 5 | F2 = 1.00 | 0.37 |
| Prior substance abuse | < 5 | 0 | 0 | — | — |
| Other‡ | 5 (8) | 0 | 0 | — | — |
| Clinical assessment scores | |||||
| Hamilton Depression Rating Scale | 4.3 (3.6–5.0) | 2.6 (1.7–3.5) | 1.9 (0.9–2.9) | F2,125 = 9.22 | < 0.001 |
| Young Mania Rating Scale | 1.9 (1.4–2.3) | 1.5 (0.9–2.1) | 1.4 (0.8–2.1) | F2,125 = 0.71 | 0.49 |
| Major Depression Inventory | 7.7 (6.3–9.5) | 4.6 (3.5–6.1) | 3.5 (2.0–6.3) | F2,119 = 6.75 | 0.002 |
| State–Trait Anxiety Inventory, state | 30.2 (28.5–31.9) | 27.2 (25.3–27.5) | 26.3 (24.2–28.6) | F2,125 = 4.43 | 0.01 |
| State–Trait Anxiety Inventory, trait | 39.7 (38.0–41.5) | 33.0 (31.2–35.0) | 34.1 (32.0–36.4) | F2,125 = 14.88 | < 0.001 |
| Visual analogue scale, happiness | 5.0 (4.6–5.4) | 6.1 (5.6–6.6) | 5.8 (5.2–6.4) | F2,124 = 6.15 | 0.003 |
| Visual analogue scale, sadness | 1.2 (0.9–1.6) | 0.7 (0.3–1.2) | 0.8 (0.3–1.3) | F2,123 = 1.73 | 0.18 |
| Visual analogue scale, vigilance | 3.7 (3.0–4.4) | 3.7 (2.8–4.6) | 5.6 (3.5–7.7) | F2,121 = 1.93 | 0.15 |
| Visual analogue scale, anxiety | 0.8 (0.5–1.0) | 0.5 (0.1–0.8) | 0.4 (0.0–0.8) | F2,123 = 1.26 | 0.29 |
| Visual analogue scale, dizziness | 0.6 (0.4–0.9) | 0.6 (0.3–0.9) | 0.3 (−0.1 to 0.6) | F2,123 = 1.43 | 0.24 |
| Visual analogue scale, nausea | 0.4 (0.2–0.6) | 0.4 (0.2–0.7) | 0.3 (0.0–0.6) | F2,123 = 0.36 | 0.7 |
LQ = lateral quotient; NA = not applicable.
↵* Unless otherwise indicated, descriptive and clinical variables are presented as estimated group means with confidence intervals calculated using a mixed-model procedure, accounting for dependence within twin pairs. Group comparisons of affected, high-risk and low-risk twins are reported with F values and p values. Counts of fewer than 5 were suppressed owing to data privacy guidelines.
↵† Measured by the Danish adult reading task; 9 participants with dyslexia were excluded.
↵‡ Attention-deficit/hyperactivity disorder, eating disorder, adjustment disorder.