Data on the occurrence of definite or definite/subthreshold OCD in FDRs of probands considering the age of symptom onset were reported for eight different samples in 12 publications [5, 16, 18, 23, 25–29, 66, 68]. However, eight studies did not present the number of relatives included in their studies, remaining only four samples for the statistical analyses [16, 18, 26, 68]. Together, the studies showed a high heterogeneity for the analyzed outcomes (definite OCD, I2 = 71%; definite/subthreshold OCD, I2 = 95%) (Fig. 4).
