Limitations for this study include sample size, and ascertainment strategies that may bias towards earlier age of onset which could result in uneven representation of disease subclasses among males and females. For example, early-onset OCD is reportedly slightly more heritable than adult-onset (Davis et al. 2013; G. Nestadt et al. 2000; van Grootheest et al. 2005). Thus, uneven representation of males and females in the early- and adult-onset OCD groups could confound heritability if estimates are influenced by both sex and age-at-onset. Age-of-onset information is incomplete in many of the historical sample collections that have been included in this meta-analysis. The lack of detailed clinical data limits our ability to address many important questions related to symptom type, symptom severity, and age of onset. These limitations underscore the need for larger OCD datasets phenotyped in greater detail to delve deeper into both genetic and clinical sex differences observed in OCD.
