Table I. Twin studies of OCD.
Adapted from ref 5: Pauls DL. The genetics of obsessive compulsive disorder: a review of the evidence. Am J Med Genetics C: Sem Med Genet. 2008; 148:133-139. Copyright © Wiley-Liss 2008
| Study type | No of twin pairs | MZ concordance | DZ concordance |
| Case studies | |||
| Lange7 | 3 | 1/2 | - |
| Le Gras8,9 | 1 | 1/1 | - |
| Lewis10 | 3 | 2/3 | - |
| Tarozzi11 | 1 | 1/1 | - |
| Rüdin12 | 1 | - | 0/1 |
| Tienari13 | 11 | 10/11 | - |
| Parker14 | 2 | 0/2 | - |
| Wooddruff & Pitts15 | 1 | 1/1 | - |
| Inouye16 | 14 | 8/10 | 1/4 |
| DSM-III/DSM-III-R OCD | |||
| Marks et al17 | 1 | 1/1 | - |
| Tarsh18 | 1 | - | 1/1 |
| Hoaken & Schurr19 | 1 | 0/1 | - |
| McGuffin & Mawson21 | 2 | 2/2 | - |
| Carey & Gottesman21 | 30 | 13/15 | 7/15 |
| Torgerson22 | 12 | 0/3 | 0/9 |
| McKeon et al23 | 1 | 0/1 | - |
| Mahgroub et al24 | 1 | 1/1 | - |
| Kim et al25 | 1 | 1/1 | - |
| Andrews et al26 | 48 | 0/18 | 0/30 |
| Lewis et al27 | 3 | 3/3 | - |
| Cryan et al28 | 1 | 1/1 | - |
| DSM-IV | MZ tetrachoric r | DZ tetrachoric r | |
| Bolton et al29 | 854 | 0.57 (0.24-0.80) | 0.22 (-0.02-0.43) |
| Tambs et al30 | |||
| OC behaviors | h2 | ||
| Young et al31 | 32 | 0 | |
| Torgerson32 | 99 | 0.18 (men); 0.23(women) | |
| Clifford et al33 | 419 | 0.44(traits); 0.47(symptoms) | |
| Jonnal et al34 | 527 | 0.33(obsessions); 0.26(compulsions) | |
| Eley et al35 | 4 564 | 0.65 (OC behavior) | |
| Hudziak et al36 | 4 246 | 0.45-0.61 |