A subset of first-degree relatives also completed a portion of the medical questionnaire (n = 1045). Approximately 60% had probable or definite OCD, and these first-degree relatives were on average younger at the time of assessment than those without OCD [34.9 ± 19.2 vs. 50.3 ± 17.7 years, t(1043) = −13.974, p < 0.001, n = 1045]. Table 3 compares prevalence of immune-related comorbidities in first-degree relatives with and without OCD for conditions with available data from at least 5% of participants in each group. Similar to OCD-affected probands, the self-reported lifetime prevalence of RF, encephalitis or meningitis, and scarlet fever was greater than expected compared with population rates. There was no difference in prevalence between OCD-affected and unaffected first-degree relatives (Table 3), although the study was insufficiently powered to detect differences in prevalence less than two-fold for each condition.
