The current meta-analysis included all OCD family and twin studies published until September 2021. The results update and extend the findings of the previous meta-analysis published more than 20 years ago [19]. The main findings were that OCD is highly familial, particularly in children and adolescents; that the heritability of OCS in twin samples is approximately 0.5; and that the higher OCS correlations between MZ twins were mainly due to additive genetic or to non-shared environmental components. These results are relevant for future genetic and clinical studies and reinforce the need for the development of specific guidelines for the screening of OCS in the FDRs of OCD subjects and the early referral for treatment when needed.
