We examined 2 subphenotypes in this article: (1) we measured lifetime OCD symptom severity using Y-BOCS35; and (2) we further considered hoarding as a second subphenotype based on 2 separate, validated measures of the hoarding construct. We focused on hoarding as a subphenotype, since its familiality is stronger than other OCD subphenotypes,36 which is further reflected by 2 recent significant linkage analyses.19,20 The Y-BOCS symptom checklist was used to derive factor scores for the hoarding symptom dimension using principal component analysis and the Varimax procedure, as previously reported.37 The factor analysis generated a factor score for each subject representing the correlation of their symptom profile with the hoarding factor, factor IV, as reported previously.37 Because the hoarding factor was essentially independent (factor loading=0.85) from the other 3 factors identified in our sample (factor loading on the hoarding factor by other factors, 0.01-0.16) and likewise by others,36-38 the hoarding factor scores were standardized, with a mean of 0 and an SD of 1. Subjects were dichotomized on the basis of scores greater than 0 or less than 0 on the hoarding
