It has been observed that early-onset OCD is more heritable (h2 = 45–65%) than adult-onset OCD (h2 = 27–47%) [16], [46]. To test this hypothesis in our data, the OCD sample was divided by age of diagnosis into early-onset (<16 years), yielding 732 case samples with early-onset OCD, and 267 case samples with adult-onset OCD. The heritability for early-onset OCD was 0.43 (se = 0.10) and for adult-onset was 0.26 (se = 0.24)( Table 1 ).
